THE AMERICAN JOURNAL OF ANATOMY 188:221-238 (1990)
Microscopic Examination of Porcine Conceptus-Maternal Interface Between Days 10 and 19 of Pregnancy J.L. KEYS AND G.J. KING Department of Animal and Poultry Science, The University of Guelph, Guelph, Ontario, Canada N l G 2 W l
ABSTRACT Conceptus-maternal interactions in the pig were examined at days 10, 13, 16, and 19 of pregnancy. Contact between the chorion and uterine epithelium was not preserved on day 10, but extensive contact occurred in 3 of 5 pregnant gilts on day 13 and was related to localized differentiation of the uterine epithelium. Attachment events occurred earlier and more rapidly than previously reported, commencing in the region of the embryonic disc and progressing toward the extremities of the chorionic vesicle, with stages from apposition through attachment occurring simultaneously along a conceptus at day 13 and thereafter. Apical protuberances on maternal epithelial cells and interposing blunt chorionic processes were evident at sites of early maternalconceptus interaction, but were reduced at regions exhibiting microvillous interdigitation. Placentation in the pig represents a developmental process consisting of a continuum of sequential events which occur over a broad time frame rather than at specific discrete times.
MATERIALS AND METHODS
Nulliparous crossbred (Yorkshire X Landrace) gilts of similar age and weight were observed daily for estrus in the presence of a vasectomized boar. Following two estrous cycles of normal duration (18 to 22 days), animals were randomly assigned for slaughter a t day 10, 13, 16, or 19 (n=Mgroup). Gilts were inseminated with approximately 50 ml of fresh unextended semen on the first day of standing estrus (day 0) and 24 h r later. Uteri from gilts which had been bred but did not contain normally developed blastocysts were discarded. The reproductive tract was removed from each animal immediately following exsanguination and trimmed free of the mesometrium. The right uterine horn was opened along the anti-mesometrial aspect; and two 20 cm segments were excised, pinned endometrial side up in a wax-based steel tray containing 0.2M cacodylate buffer (pH 7.41, and examined under a magnifier-illuminator in order to locate the conceptuses a t day 13 of gestation and later. Flag pins were inserted lateral to the embryonic disc(s). Upon removal of the buffer, the tissue was gently flooded with 3% glutaraldehyde in 0.2M cacodylate buffer and left to fix for 30 min a t room temperature. Endometrial samples were selected randomly from the mesometrial region of pregnant uteri at day 10 INTRODUCTION since the blastocysts were not attached to the mucosa. Despite the essential role the porcine uterus plays in To investigate whether epithelial adaptations for emthe establishment of pregnancy, alterations in the lu- bryonic attachment were localized to regions of trophominal epithelium which occur during preimplantation blast proximity or represented a generalized uterine stages and initial placental development have not been response, 3 mesometrial regions were sampled along widely studied. With few exceptions (Corner, 1921; each of 2 embryos within each gravid uterus at day 13 Stroband et al., 1986), investigators have neglected to and later: 1) immediately adjacent to the embryonic elucidate structural alterations which are pregnancy- disc, 2) approximately 5 cm from the disc with adherent specific by comparing pregnant endometria with tissue membranes, and 3) from sites lacking trophoblastic on corresponding days of the estrous cycle. In addition, contact. Samples were processed for light and electron few morphological studies have been designed to study microscopy as previously described (Keys and King, localized interactions between the pig conceptus and 1989). Twelve sampling sites were examined per anithe endometrium during this critical phase of the re- mal. Height measurements of surface epithelial cells were productive process. Preliminary results indicated that contact between made on 6 consecutive cells in 3 regions on each of 4 porcine trophectoderm and uterine epithelium could slides prepared for light microscopy from each samnot be preserved a t day 10, but attachment had com- pling site, resulting in 432 measurements per animal. menced by day 13 (Keys and King, 1984; Keys et al., The cell-height data were analyzed statistically by one1986). The objectives of this study were to develop a way ANOVA, and treatment means were compared comprehensive morphological description of conceptusmaternal interactions a t days 10, 13, 16, and 19 of pregnancy; to describe epithelial changes accompanying and possibly facilitating the attachment process; Received November 28, 1989. Accepted February 15, 1990. and to look for morphological evidence of a localized Address reprint requests to Dr. G.J. King, Dept. Animal & Poultry influence by the blastocyst on the structure of the ma- Science, The University of Guelph, Guelph, Ontario, CANADA N l G 2w1. ternal epithelium. 0 1990 WILEY-LISS, INC
222
J.L. KEYS AND G.J. KING
with data from contemporary cycling animals (Keys and King, 1989) a t equivalent stages using a Scheffe's test. RESULTS
Uterine epithelial cell heights on days 10 (20.382 0.37 pm), 13 (22.320.21 pm), and 16 (21.04+0.18 pm) were similar (P
Microscopic Examination of Porcine Conceptus-Maternal Interface Between Days 10 and 19 of Pregnancy J.L. KEYS AND G.J. KING Department of Animal and Poultry Science, The University of Guelph, Guelph, Ontario, Canada N l G 2 W l
ABSTRACT Conceptus-maternal interactions in the pig were examined at days 10, 13, 16, and 19 of pregnancy. Contact between the chorion and uterine epithelium was not preserved on day 10, but extensive contact occurred in 3 of 5 pregnant gilts on day 13 and was related to localized differentiation of the uterine epithelium. Attachment events occurred earlier and more rapidly than previously reported, commencing in the region of the embryonic disc and progressing toward the extremities of the chorionic vesicle, with stages from apposition through attachment occurring simultaneously along a conceptus at day 13 and thereafter. Apical protuberances on maternal epithelial cells and interposing blunt chorionic processes were evident at sites of early maternalconceptus interaction, but were reduced at regions exhibiting microvillous interdigitation. Placentation in the pig represents a developmental process consisting of a continuum of sequential events which occur over a broad time frame rather than at specific discrete times.
MATERIALS AND METHODS
Nulliparous crossbred (Yorkshire X Landrace) gilts of similar age and weight were observed daily for estrus in the presence of a vasectomized boar. Following two estrous cycles of normal duration (18 to 22 days), animals were randomly assigned for slaughter a t day 10, 13, 16, or 19 (n=Mgroup). Gilts were inseminated with approximately 50 ml of fresh unextended semen on the first day of standing estrus (day 0) and 24 h r later. Uteri from gilts which had been bred but did not contain normally developed blastocysts were discarded. The reproductive tract was removed from each animal immediately following exsanguination and trimmed free of the mesometrium. The right uterine horn was opened along the anti-mesometrial aspect; and two 20 cm segments were excised, pinned endometrial side up in a wax-based steel tray containing 0.2M cacodylate buffer (pH 7.41, and examined under a magnifier-illuminator in order to locate the conceptuses a t day 13 of gestation and later. Flag pins were inserted lateral to the embryonic disc(s). Upon removal of the buffer, the tissue was gently flooded with 3% glutaraldehyde in 0.2M cacodylate buffer and left to fix for 30 min a t room temperature. Endometrial samples were selected randomly from the mesometrial region of pregnant uteri at day 10 INTRODUCTION since the blastocysts were not attached to the mucosa. Despite the essential role the porcine uterus plays in To investigate whether epithelial adaptations for emthe establishment of pregnancy, alterations in the lu- bryonic attachment were localized to regions of trophominal epithelium which occur during preimplantation blast proximity or represented a generalized uterine stages and initial placental development have not been response, 3 mesometrial regions were sampled along widely studied. With few exceptions (Corner, 1921; each of 2 embryos within each gravid uterus at day 13 Stroband et al., 1986), investigators have neglected to and later: 1) immediately adjacent to the embryonic elucidate structural alterations which are pregnancy- disc, 2) approximately 5 cm from the disc with adherent specific by comparing pregnant endometria with tissue membranes, and 3) from sites lacking trophoblastic on corresponding days of the estrous cycle. In addition, contact. Samples were processed for light and electron few morphological studies have been designed to study microscopy as previously described (Keys and King, localized interactions between the pig conceptus and 1989). Twelve sampling sites were examined per anithe endometrium during this critical phase of the re- mal. Height measurements of surface epithelial cells were productive process. Preliminary results indicated that contact between made on 6 consecutive cells in 3 regions on each of 4 porcine trophectoderm and uterine epithelium could slides prepared for light microscopy from each samnot be preserved a t day 10, but attachment had com- pling site, resulting in 432 measurements per animal. menced by day 13 (Keys and King, 1984; Keys et al., The cell-height data were analyzed statistically by one1986). The objectives of this study were to develop a way ANOVA, and treatment means were compared comprehensive morphological description of conceptusmaternal interactions a t days 10, 13, 16, and 19 of pregnancy; to describe epithelial changes accompanying and possibly facilitating the attachment process; Received November 28, 1989. Accepted February 15, 1990. and to look for morphological evidence of a localized Address reprint requests to Dr. G.J. King, Dept. Animal & Poultry influence by the blastocyst on the structure of the ma- Science, The University of Guelph, Guelph, Ontario, CANADA N l G 2w1. ternal epithelium. 0 1990 WILEY-LISS, INC
222
J.L. KEYS AND G.J. KING
with data from contemporary cycling animals (Keys and King, 1989) a t equivalent stages using a Scheffe's test. RESULTS
Uterine epithelial cell heights on days 10 (20.382 0.37 pm), 13 (22.320.21 pm), and 16 (21.04+0.18 pm) were similar (P
