hemopoietic cells, possibly involving cell contact, while the second, potentially systemic, control system involved specific regulatory molecules. Characterization of these latter hemopoietic regulators in the past 20 years has required a combination of technical advance5 in three areas: the development of culture systems able to support the selective growth of differentiating cells of the various hemopoietic lineages or corresponding continuous hemopoietic cell lines; advances in the ability to purify and sequence minute amounts of glycoproteins; and, above all, the use of molecular biology to isolate and express the genes encoding the various hemopoietic regulators.

Summary A large, and growing, group of glycoprotein rcgulators is now recognized to control the proliferation, maturation and functional activity of the eight major families of blood cells. Each hemopoietic regulator is the product of multiple cell types and there is a puzzling redundancy of regulators able to stimulate each subfamily of heniopoietic cells. Each regulator is polyfunctional but it remains unclear how a single type of activated receptor is able to initiate the diverse cellular responses induced. Introduction The regulation of blood cell formation (hemopoiesis) presents some formidable problems. Hemopoiesis is required to be continuous throughout life, to be self-sustaining, to generate maturing cells in eight distinct lineages from a common set of precursor cells and to be achieved with precision yet be ablc to be expanded rapidly on demand. As early as the mid-l960’s, analysis of the regulatory processes involved had indicated that two interacting systems were involved. The first was some form of local control by specialized stromal cells within the scattered deposits of

The Hemopoietic Regulators From these combined approaches, identification of the specific regulators involved has made impressive progress. So far, 17 distinct hemopoietic regulators have been identitied, their cDNA’s cloned and the regulators produced in active recombinant form (Table I). Four of these, erythropoietin, G-CSF, GM-CSF and ZL-2are now licensed for clinical use, while others such as E-3, IL-4 and IL-6, are in various stages of clinical or preclinical trial. However, the framework of knowledge surrounding each of these regulators is quite variable and for the most part incomplete. This applies particularly to the more recently described regulators where discovery was made by expression cloning, often using abnormal target cell lines, with little or no clue regarding the possible normal role of the regulator concerned. Even where there has been a more classical sequence of discovery, followed by stepwise protein purification and then cDNA cloning, there is still an incomplete understanding of the true role of such regulators in the biology of hemopoiesis. This essay will not attempt a summation of the infortnation available as much of this material has been reviewed in detail el~ewherecl-~). An opportunity is taken here to com-

Table 1. The hernopoietic regulators in the mouse Molecular mass of polypeptidc I>a

Regulator

Erythropoietin, Granulocyte-macru~ha~c colony-stimulating factor Granulocyte colony stimulating factor Macrophage colony stimulating facLor

Epo GM-CSF G-CSF M-CSF (CSF- 1)

Multipotential colony stimulating factor, Interleukin- 1 Interleukin-2, Interleukin-4, Intcrleu ki n-5, Interleukin-6, Intcrlcukin-7, Interleukin-9, Interleukin- 10, Interleukin-1I , Interleukin- 12. Stem cell factor (Steel factorkit ligand), Leukemia inhibitory factor,

Multi-CSF (IL-3) IL- 1 IL-2. IL-4 lL5 IL-6 IL-7 IL-9 IL-10 IL-11 IL-12 SCF

~

LIF

18,400 14,400 i9,ino 21 ,00O(X2) 18,00O(X2) 16,1100 17,900 19,400 14,000 l3,3OO(X2) 2 1.700 14,900 34.200 18,700 2 1,000 I

18,400 20.000

Responding hcmopoietic cell’:

G,M,Fa,Meg,Mast,E.Stem T,Stem T,B B,T.G,M,Mast h,B B,G,Stem,Meg B,T ‘I‘,Meg,Mast T Me&B N K. Stern,G,E,Meg,Mast Meg

G=granulocytcs. M=macrophagcs, Eo=eosinophls. E=erythroid cells, M=megakmyocytes, Stem=stem cells, Mast=mast cells, T=l’-lymlphocytes, R=H-lymphocytes. N.K.=natural killer cells.

inent on some of the patterns and problems emerging in this field. It is intriguing that the body has elected to use as proliferative hemopoietic regulators a rather similar group of glycoproteins with a polypeptide chain molecular mass of 1321x103 Da. The native glycoproteins actually dirfer much more widely in mass because of highly variable glycosylation but this carbohydrate is not involved in the active binding sites and appears merely to modulate the degradation and clearance of the molecules in vivo. There is ininimal evidence of amino acid sequence homology between the regulators although it has been suggested that some may have a generally similar three-dimensional configuration involving four a helical bundles, two of which contribute to the specific combining si te(7). There are three methods by which hemopoietic regulators are presented to responding hemopoietic cells: (a) membrane display on stromal cells to stimulate hemopoietic cells bound to the stromal cells, (b) local production of regulators where their range of action may be restricted by the low concentrations produced and/or the short half-life of the molecules, and (c) production by distant cells with transport through the circulation as conventional hormones (Fig. 1). Some, such as M-CSF, are involved in all three modes of presentation@) but, for most, no transcript is produced permitting membrane display. For the latter, the relative importance of local versus systeinic production probably varies according to circumstances. This diversity of presentation may be designed to allow the regulators to acl both on immature cells (in the marrow) to generate maturing progeny and also to act on the mature cells after they have been released from the marrow and have entcred various distant tissues. The restricted location of hemopoiesis to the marrow and spleen makes it evident that specialized local stromal cells in these tissues must play a key role in controlling, or at least permitting, hemopoiesis. This has been confirmed by a variety of in vivo observationd9) and culture studies showing that

Blood Vessel

Stromal Cells Fig. 1. Hemopoietic regulators can be displayed on the membrane of producing cells (1) and there stimulate attached hemopoietic cells. Alternatively the regulators can be locally produced and influence only adjacent cells (2) or can be produced elsewhere in the body and bc delivered to hemopoietic cells via the circulation (3).

stromal cell contact with hemopoietic cells is of importance in maintaining multipotential stem cell numbers and the generation by them of progenitor cclls committed to hemopoietic"O) or lymphoid(' I ) lineages. What remains uncertain is how this special role is actually accomplished. Do stroinal cells produce unique regulatory molecules of crucial importance for the biology of stem cells? This remains a distinct possibility although studies so far have merely demonstrated their capacity to make a number of the regulators listed in Table 1, regulators that are certainly also able to be produced by a variety of cells elsewhere in the body. An alternative possibility is that the action of a particular regulator may be significantly modulated if the context in which it binds to its receptors on hemopoietic cells is changed by signalling from adjacent adhesion molecule-receptor complexes.

The Receptors for Hemopoietic Regulators A s is apparent from Table 1, an obvious feature of the control mechanisms operating on hemopoietic cclls is the redundancy of the regulators involved. For example, at least seven regulators can have some stimulating effects on the the proliferation of granulocyte precursors and eight on the proliferation or niegakaryocyte precursors. The ability of multiple regulators to act on hemopoietic cells, is made possible by coexpression of the required reccptors on individual immature and mature cells('7). Typically, the numbers of receptors of any one type on an individual hemopoietic cell are relatively small -usually a few hundred at most. Thcse are, however, of high-affinity (20-100 pM) and stimulation of the responding cells is achievable by occupancy of a quite low percentage of these receptors. While the regulators exhibit little amino acid sequence homology, their membrane receptors do exhibit evidence of relatcdness. The receptors are of two general classes: (a) transmembrane glycoproteins with a tyrosine kinase domain for signalling following activation by ligand binding. Only two hemopoietic regulators have receptors in this class, SCF and M-CSF, but this group is a subset of the large immunoglobulin superfamily; (b) transmembrane glycoproteins lacking a tyrosine kinase domain that combine with at least one other receptor chain (p subunit) to forin a highaffinity receptor. This is a rapidly expanding family of growth factor receptors that includes the receptors for erythropoietin, GM-CSF, G-CSF, Multi-CSF, IL-2, IL-4, IL-6, IL-7, LIF, and Oncostatin M (OSM) as well as receptors for certain classical hormones such as growth factor and prolactin. These receptors exhibit clear homology in their extracellular and may he characterizable as having a double /3 barrel sheet configuration as exemplified by the growth hormone receptor (14). Whereas the hemopoietic regulator receptors are noncross- reactive and of high specificity it was initially puzzling to observe that binding of one regulator to its receptors could down-modulate certain of the other hemopoietic receptors on the same cell("). The basis for this trans-downmodulation still remains partly unresolved. However, recent studies on cloned receptors have provided an intriguing explanation for the common actions of certain regulators and for some unaii-

GM-CSF

Fig. 2. On human cells, the a-receptor chains for GM-CSF, IL-3 and IL-S share competitively a comtnon P-chain. The a-chain receptor only

IL-3

IL-3Ra IL-5Ra

ticipated cross-competition for apparently specific binding sites. It has now been shown that the a chains of certain receptors share competitively common p subunits, that a-P binding is necessary for high binding affinity and that the psubunit initiates signalling from the bound receptor('". l o r example, on human cells, the individual a-receptor chains for GM-CSF, I L 3 and IL-5 share competitively a common p chain, providing a molecular explanation for why all three regulators exhibit somc competitive interactions and have a common capacity to stimulate the proliferation of eosinophil progenitors (Fig. 2). A similar competitive sharing of J3 chains has been reported recently for 1L-6, LIF and OSM""). The sparcity ofrcceptors o n individual cells and the phenomenon of subunit sharing makes it highly likely that the receptors conccrned are concentrated in receptor islands on the hcniopoietic cells, unless a much greater motility of receptors on cell membranes is possible than at present seems likely.

Is There Redundancy in Hemopoietic Regulators? Given the embarrassment of riches in the apparently excessive number of regulators available to stimulate subsets of hemopoietic cells, it was logical to suppose that one reason behind the apparent redundancy might be the neccssity for sequential action of various rcgulators. In one or two extreme examples. a case can be made supporting this view. For example, SCF, a regulator with its most promincnt actions on early hemopoietic cells, could be envisaged as controlling the earliest stages of megakaryocyte formation while IL-6, which seems only to influence the proliferation of relatively mature megakaryocyte precursors, would represent a later control signal. However, this notion of sequential action has not been convincingly supported by other observations as there are many examples where multiple regulators can act in vitro on cells at an identical maturation stagc to achieve apparently identical proliferativc responses. A rather different view of the redundancy paradox emerges rrom an analysis of the biology of thcse regulators in vivo. For example, when acting in vitro, both G-CSF and GM-CSF stimulate the formation of granulocytic colonies. Howcvcr, in vivo, G-CSF has a more prominent capacity to elevate blood levels of granulocytes than docs G;2.1-CSF(17) whereas, whcn injected locally into the peritoneal cavity,

acquires high-affinity for i t s ligand after complexing with the P-chain. If this fails to occur because of competition for the b-chain, the fast offrate kinetics of low-affinity receptors result in loss of bound regulator molecule?. Only the complex formed by the combination of regulalor with both a- and P-chains is able to initiate signalling.

GM-CSF has a more prominent action in elevating cell numbers(l8). Furthermore, during infections in the and man, G-CSF is present in higher concentrations in the circulation than GM-CSF which may often merely be produced locally. These observations suggcst that the design system of regulatory control may have considerable subtlety and employ combinations of regulators with certain common cellular actions but differing in their in viva biology to achieve selective responses. It remains possible that there may be genuine redundancy of no particular value in hemopoietic regulators. The common evolutionary origin of many of the receptors involved does permit the possibility that the diversity of regulators has been the result of accidental mutation during evolution from a simpler, but quite efficient, control system. Most would argue, however, that thc evolutionary complcxity of today's mammal has required a diversity of regulators to evolve on the general grounds that therc must be certain situations in which some special aspect of each regulator confers a particular survival advantage. The need to be able to respond effectively to these rare emergencies would then require a large repertoire of regulators that may often be redundant. A resolution of some of these problems requires the demonstration of a crucial role in vivo for each regulator in controlling either normal or amplified hemopoiesis. This requires experiments demonstrating the development of a significant defect when the regulator is suppressed either by antibodies or gene deletion. To date, uncyuivocal evidence of the importance of these regulators is available only for erythropoietin(20),G-CSF(") and M-CSF(22)and comparable evidence is urgently needed for the remainder. The redundancy question has some practical aspects. The number of newly discovered hemopoielic regulators increases annually and based on the pattern already evident, the total number of regulators may well exceed 50. If regulators are now available that are adequate to promote various types of hemopoiesis, is there any particular point in the expense of discovering and developing additional regulators? The personal drive of scientists for discovery and more complete understanding is such that these considerations may be of little relevance in the research laboratory but they are certainly now of practical concern for pharmaceutical companies contemplating thc known cost of one hundred million dollars for developing each agent for clinical use.

The Polyfunctionality of Hemopoietic Regulators One striking aspect of the biology of hemopoietic and other regulators is their polyfunctionality. It had been assumed by many that, as a gencral principle, distinct regulators would control cell division while others would control maturation or the functional activity of mature cells. However, most hemopoietic regulators have been shown to have direct actions on hemopoietic cells that embrace this range of cell functions. The situalion is most clearly documented for the CSF’s. Each CSF can control not only cell division, but also differentiation commitment, maturation induction and the functional activity of mature cells(23).However, it must also be noted that the relative importance of the role played by the CSFs in these different processes probably varies. Thus the CSFs are mandatory for cell division to occur in granulocytic and macrophage populations, with a direct concentrationdependent control of the cycling status of the cells, the length of their cell cycle and the number of progeny produced by each precursor. On the other hand, while the CSFs have a readily demonstrable capacity to inlluence the survival and functional activity of mature neutrophils and macrophages, the data suggest that these latter functions are not exclusive to the CSFs since other factors can influence the same functions, sometimes in a more powerful manner. While each of Lhese actions has been shown to be a direct one of the CSFs on responding cells, the CSFs can also initiate changes in the levcls of other regulatory molecules that can result in additional effects on the targel hemopoietic cells. The ability of the CSFs and other hemopoietic regulators to exhibit such an astonishing range of actions on responding cells raises some intriguing questions concerning the mcchanisms that need to be activated within the cells to achieve such diverse responses. An explanation is also needed for why one cell responds to signalling by cell division while mother responds merely by producing some cell product. To rcgulate cell division. CSF-initiated signalling must eventually have an impact on the complex events occurring within the nucleus during the cell cycle. Similarly, to induce irreversible differentiation comnii tment presumably requires at a minimum the activation of a particular set of nuclear transcription factors as does the initiation of maturation, although the latter process presumably involves a quite different set of genes. At the other extreme, the actions of a CSF in maintaining membrane transport integrity or in enhancing the production of superoxide by a mature neutrophil may wcll involve events that arc restricted to local cytoplasmic regions. How can these diverse actions be initiatcd by a single type of activated receptor? It is already known that, at a minimum, the activation of most hemopoietic receptors involves either the coupling of two receptor chains by dimer formation in the case of the tyrosine kinase-type receptors or CL-pchain heterodimer forniation by the larger group of hemopoietic rcgulator receptors. T h s permits the possibility that qualitatively different signals might be generated from each of the chains of the activated receptor complex, one perhaps initiating nuclear-directed signalling, the other cytoplasmic. The conl-

plexity emerging for the structure of the T-cell antigen receptor(24)provides another possible structural mechanism by which divergent signalling might be achieved. It may be that additional molecules (that may or may not be formally definable as receptor subunits) are associated with the a-p complexes of hemopoictic regulator receptor possible that distinct signalling cascades such associatcd molecules. Such an arrangement need not be mandatory, but if it exists and the composition of the receptor complex varies in cells at different differentiation stages, it would be helpful in providing a physical explanation for the differing effects of a regulator on cells at different stages of maturdtion. A general alternative is that multiple molecules in cellular signalling pathways may be able to interact with different portions of a rcceptor chain, allowing an activatcd receptor to initiate multiple sigalling streams(25).Again, the nature of these moleculcs could vary at different stages of cellular differentiation. When the first hemopoietic regulator, erythropoietin, was characterized, it appeared to have a highly selective action limited to the late stages of red cell formation. This led to the expectation that selectivity of responding cells might also be a feature of other hemopoietic regulators. To a degree, the second generation of hemopoietic regulators. the CSFs, supported this notion of selective action. However, on further analysis, the CSFs differed in that their range of target cells clcarly was broader than the original action demonstrated on granulocytic and macrophage populations (Fig. 3). For example, GM-CSF can also stimulate the proliferation of eosinophil, megakaryocyte and some erythroid cells(26) while Multi-CSF (IL-3) has in addition a capacity also to stimulate mast cell and stem cell proliferation(27).It is now becoming evident that the CSF’s can even have actions on cells outside the hemopoietic population. GM-CSF and GCSF have both been reported to stimulate endothelial cells(28)while M-CSF and GM-CSF have actions on placental ceWgJ*). Certain hemopoietic regulators exhibit an extreme degree of polyfunctionality. For example, LIF has powerful direct actions on embryonic stem cells, neurones, hepatocytes, adipocytes and osteoblasts at the same concentrations as used LO demonstrate their actions on hemopoietic cells‘31) and a comparable broad range of actions has bcen described for lL-6(32). Thcse latter molecules havc raised some biological issues of disturbing proportions. It is possible to dismiss the extraordinary range of responding cells by saying that the regulators were misclassified - that they are general tissue regulators, not really different in principle from cerlain classical hormones that also have actions on a broad rangc of cells. However this merely avoids the real issue. Why would the body choose to use the same highly specific molecule to achieve such diverse responses? Are there really situations where all such cells must respond in unison and, if not, why use a non-specific signalling system with the built-in capacity for inducing unwanted effects? The problem may reflect our present over-enthusiasm for the concept that different cell populations are likely to have ‘private’ regulatory systems or our incomplete awareness of the integrated nature of different organ systems. However. using the normally reli-

Megakaryocytes

Neutrophils

Early erythroid cells

@

+

@Macrophages /”

0- I GR/I-CSFI -@ Placenta

Embryonic stem cells

Eosinophils

‘@Megakaryocytes

Sensory and autonomic neurones

cells

detectable in the circulation, and so LIF produced locally in the brain could influence neuronal function and signalling without unwanted actions elsewhere. The multiplicity of likely local sites of LIF production could pernlit this regulator to act on diverse tissues in an essentially independent, organ-restricted manner. A feature of the biology of at least some hemopoietic rcgulator-receptor systems is the production of smaller, secreted, versions of the receptor that contain the ligand- binding site. The soluble receptors for IL-2(331,IL-6(34)and LIF are present in the circulation and could act as blocking agents. While the system is conceptually bimrre, it could permit a polyfunctional regulator to have localized actions without producing unwanted systemic cffccts. For IL-6, the difficulty with this explanation is that the IL-6-solublc IL-6 receptor complex has been reported not to be functionally silent but to be able to bind to the p-chain (pp 130) and activate intracellular ~ignalling(~5,.

Where are Hemopoietic Regulators Produced? It is not possible to state with confidence which cells in the body are able to produce most of the known regulators. With erythropoietin, the simplest cxample, since in adult life most erythropoietin is made in the kidney, initial evidence suggested that erythropoietin might be produced by glomerular cells(”) but it now seems likely that erythropoietin is produced by interstitial cells adjacent to the renal ~ u b u l e s ( ~For ~’. the other rcgulators, the situation is more difficult. In general, it is possible to say that the amounts of these regulators produced are normally very small and that they are the products of multiple cell types dispersed throughout the body. In the case of the CSFs, cell types with an ability to produce one or other CSF include stromal cells, endothelial cells, fibroblasts, macrophages, lymphocytes and some epithelial cells“). The ability of products of microorganisms to elicit prompt increases in CSF mRNA levels and mature protein production by these cells(”), permits the probably correct conclusion that CSF-producing cells are distributed widely and are of diverse types, simply to ensure that they can make early contact with the products of invading microorganisms. The true situation may differ only in that possibly all cells in the body can produce CSFs of one type or another after appropriate inductive signalling. The reason why other cells have not yet been identified as potential CSF producers is simply that it is not yet technically feasible to obtain absolutely pure populations of most mammalian cell types to test in vitro under appropriate conditions. There are two major problems underlying our present inability to identify which cells make hemopoictic regulators. First, the levels of regulator production are too low for most bioassay systems to detect and usually too low to be detected by in situ hybridization or labeled monoclonal antibodies. Second, the methods used to prepare a pure population of cells and the subsequent culture of the cells for analysis are themselves powerful inducing signals that can lead to a thousand-fold rise in levels of mRNA or protein production. Under these circumstances, most of the published information describes the potential capacity of the cells under

s/z@yjf Adipocytes Gonads

asts

Megakaryocytes

Fig. 3. Examples of increasing diversity in the range of cells responding to hemopoietic regulators: (1). Erythropoietin (Epo) action is restricted to late stage erythroid and somc megakaryocyte precursors; (2). GM-CSF acts on a broader rangc of hcmopoietic cells and also on placental cells; (3). Leukemia inhibitory factor (LIF) has opposite actions on myeloid leukemic cells and normal crnbryonic stem cells and has also major actions on hepatic cells, neurones, osteoblasts, adipocytesand gonadal cclls in addition to its actions on inegakaryncyteformation.

able guidance of naturally-occurring disease states or genetic defects, there are no situations presently known where, in an adult, it seems necessary to coordinate the function of such diverse tissues as bone, liver, brain and hemopoietic cells. There is one aspect of the biology of hemopoietic regulators that may resolve the problems potentially posed by these polyfunctional regulators. A prominent feature of the hemopoietic regulators is their ability to be produced, and act, locally. For the CSFs this allows the body where appropriate to employ CSFs to regulate new cell production in the marrow but, independently, using the same regulators to selectively influence the functional activity of a set of mature neutrophils or macrophages in a remote focus of skin infection. Does local production and action of LIF allow it to be used as an effective but diverse regulator? LLF is not normally

study and provides no secure information on the actual activity of the corresponding cells in viva If some type of PCR-in situ hybridization could be devised, it might partly resolvc this technological impasse.

Do the Hemopoietic Regulators Point the Way to the Future? To what degree are the cellular events and regulation of hemopoiesis unusual in the mammal? There are obvious differences between hemopoietic and other cells, the most apparent of which are the controlled movement and function ofthe hemopoietic progeny elsewherc in the body. Thesc can be presumed to require regulatory mechanisms of some novelty. Nevertheless, much of what occurs in hemopoiesis is comparable with events in the skin or gut - the sustained cell generation, commitment dccisions, maturation induction and the regulation of specialized functions. The ordered architecture of such tissues has focused much attention on regulatory control based on local cell-cell interactions but in hemopoiesis such apparcnt cell-cell interactions have proved to involve regulatory molecules that are not exclusively produced locally. It seems probable that the control of gut or skin will be found to involve an equally complex set of regulators to those involved in hemopoiesis, raising the same types of issues as have been discussed above. Entry into this world of organ regulators will require application of the same technologies that were needcd for the hemopoietic regulators, the key requirement bcing the development of adequate culture systems for the cell typcs under study. In retrospect, much of the discovery of hemopoietic regulators could have been accomplished using neoplastic hemopoietic cells either as sources of the regulators themselves or as target populations able to display at least some responses. If difficulties continue in the separation and culture of various normal organ cells, a useful beginning should be possible by using existing heoplastic equivalents that are able to be cultured in v i m . While the riches of hemopoietic regulators are beginning to prove an embarrassment for their understanding and practical application, it is likely that these problems will not remain exclusive to experimental hematologists for much longer. References 1 Metcalf, D. (1988).The Molecuhr ConZrol oftlkuud Cells. Hiward UniversityPress. Cambridge. 2 Metale, D. (1991). The colony-stimulatingfactors: discoveiy to clinical use. Phil. T r m . R. Suc. hind. B 333,147-173. 3 Demetri, G. D. and Griffin, J. D. (1991). tiranulocyte colony- stimulating factor and its receptor. Blood 78,2791 -2808. 4 Casson, J. C. (1991). Molecular physiology of granulocyte-macrophap colonystimulating factor. Blood77,1131-1145. 5 Cmldwasser, E., Beru, N. and Smith, D. (1990). Erythrnpoietiu. In Colony Sfirnuhfing Factors, (cd T.M.Dexter, J. M. earland and N. Testa), pp. 257-276. Miml Dekker. N.Y. 6 Hirano, T. (1991). lnterlcukin 6 (L-6) and its rerxptor: Their role in plasma cell ncoplasias.Inf.J. Cell Cloninx 9, 116-1 84. 7 Bazan, 1. F. (1990). Haemopoietic mceptnrs and helical cytokines. Immunolog); 7uflay 11,350-354. 8 Rettenmier, C. HI., Roassel, M. F., Ashmun, R. A., Ralph, P., Pric!, K. and Sherr, C. J. (1987). Synthcsis of membrane-bound colony-stirnularing factor 1 (CSF-

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Hirano. T. and Kishimoto, T. (1989). Interleukin 6 trigger5 the association of its receptor with a possible signal transducer gp 130. Cell 58,573-581 36 Mori, S., Saito, T., Morishita, Y., Saito, K., Urabe, A., Wakabayashi, T. and TakaRu, F. (1985). Gloinerular cpitheliurn as the main locus of crythropoictin i n hurnao kidney. J L I ~ JU. Exp. ~ Mcd. 55,69-70. 37 Koury, S. T.. Koury, 41. J., Ilondurant, M. C., Cairo, J. and Graber, S. E. (1989). Qiiantitation of erythropoietin-producing cells in kidneys of mice by in situ hybridization: Correlation with hcmatocrit, rcnal crythropoictin mRNA and s c r m crythropoictin conccntration. Hlood?4,645-65 I . 38 Gough, N. M. and Nicola, N. A. (1990). C;rallu~ocyle~nincrophage colony-

stimulating t'actor. In C o t m y Stiiniriuting I;ncriJrs(ed. T. M. Dexler, I, M. Garland arid N. G.Testa),pp. 111-153.Marcel DekkerKY.

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is at The Walter and Eliza Hall Institute of p.0. ~~~~l Melbourne ~ ~ ~ 3050 ~ i Victot ~ l , ria, Australia. ~ _ _ _ _ _

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THE NEW YORK ACADEMY OF SCIENCES

Human Reproductive Ecology: Interactions of Environment, Fertility and Behavior May 21 to 24,1993 Sheraton Imperial Hotel and Convention Center, Research Triangle Park, North Carolina The low fertility of contemporary industrialized nations is recent and historically unique. Given that reproductive physiology did not evolve to function optimally in its environment, what can we learn about human reproduction from the study of preindustrial populations? Are high Icvels of fetal loss and widespread pathological sterility inherently human, or are they recent devclopments? Does amelioration of the industrial environment or of nutrition and health measurably alter fecundity? In non industrialized regions such as sub-Saharan Africa, where high fertility and rapid population growth are associated with deterioration of both the biotic cnvironments, how do fecundity and firtilily respond to environniental change? This interdisciplinary conference explores these and related issues. Topics include: the roles of seasonality and nutrition in human fertility; biobehavioral interactions affecting fecundity and fertility; reproductivc epidemiology with special attention to pregnancy loss and pelvic inllammatory diseases; the design and conduct of studies in reproductive ecology; analytical standardization and controls; public health issues including contraception, lactation, and childhood malnutrition; and an examination of the role of fertility in population growth. Conjerence Steering Cnrnmittee Kenneth L. Campbell, Ph.D. Associatc Professor of Biology University of Massachusetts at Boston 100 Morrisscy Boulevard Boston, MA 02125-3393

James W. Wood, Ph.D. Associate Professor of Anthropology 409 Carpenter Building Pennsylvania Starc University University Park, PA 16802

There will be contributed poster sessions in conjunction with this conference and these will form an integral part of the program. The deadline for submission of poster abstracts is February 1, 1993. The entire abstract, including title, author(s), and affiliations, must be typed single-spacc and contained within a rectangle that measures 5" x 4$' (wxl). (Abstract form is not necessary.) Abstracts should be sent to: Dr. Campbell at the above address. For further information Lontact Confercnce Department, New York Academy of Sciences 2 East 63rd Street. New York, NY 10021, USA. Phone (212) 838-0230 Fax (212) 888-2894 Cable NYACSCI -~___ ____ ~- . __ _ _ I

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