Placental expression of major histocompatibility complex class I in bovine somatic clones

Abnormally increased placental expression of major histocompatibility complex class I (MHC-I) molecules at the trophoblastic surface has been suggested previously to be the cause of early fetal loss in nuclear transfer (NT) bovine pregnancies. Here, we report the lack of expression of MHC-I at the trophoblastic surface at D30 and D60 and in placentomes from D60 to term in placentas obtained by NT from three different genotypes and by artificial insemination, whatever the outcome of the pregnancy. MHC-I expression was assessed by immunohistochemistry using four different antibodies, including a novel beta2-microglobulin antibody. The MHC-I type of the clones was established using reference strand-mediated conformation analysis (RSCA); however, since it proved problematic to type the recipient animals in the same way, outcome of pregnancy could not be related to MHC compatibility. In conclusion, the present study provides no evidence to support abnormal expression of MHC-I on the trophoblastic surface in clones as a major cause of fetal loss during pregnancy after NT.

Large Offspring or Large Placenta Syndrome? Morphometric Analysis of Late Gestation Bovine Placentomes from Somatic Nuclear Transfer Pregnancies Complicated by Hydrallantois

Somatic nuclear transfer (NT) in cattle is often complicated by fetal oversize (i.e., large offspring syndrome), hydrallantois, and placentomegaly in late gestation. The aims of this work were to obtain data on the placentome structure in NT-recipient cows with hydrallantois (NTH) and to relate these with fetal and placental weights to better understand the abnormalities observed in NTH pregnancies during the third trimester. Pregnant cows were slaughtered between Gestation Days 180 and 280. The fetuses were weighed, and the placentomes were numbered and weighed. Placentomes were examined by histologic and stereological techniques. Macroscopic data showed that placental overgrowth preceded fetal overgrowth, and the ratio of the fetal to the total placentome weight in the NTH group was lower than that in controls after Gestation Day 220. This suggests that placental overgrowth is due to placental default rather than due to fetal overgrowth, as shown also by stereological analysis showing primary deregulation of the growth of cotyledonary tissues. Observed alterations, such as thinning of the maternal epithelium within placentomes and increased trophoblastic surface, could be secondary adaptations. Thus, placental growth deregulations would be due to modifications of the expression of placental factors. Various examples of placental deficiency were observed, suggesting that some fetal abnormalities observed in NTH calves, such as enlarged heart, enlarged umbilical cord, and abdominal ascites, are consequences of placental dysfunction. Therefore, the condition described by the term "large offspring syndrome" might better be described by "large placenta syndrome," because this syndrome affects an average of 50% of late-gestation NT pregnancies. No conclusion can be drawn from this work on apparently normal pregnancies.

Expression of growth hormone and its receptor in the placental and feto-maternal environment during early pregnancy in sheep

In a previous study we showed the existence of GH in the ovine placenta. We now supplement the information available on placental GH and describe the presence and distribution of GH receptor (GH-R) messenger RNA (mRNA) in uterine, fetal, and placental tissues during early pregnancy. GH mRNA was not detected in the placenta before day 27 (d27). Its expression peaked between d40 and d45 and fell after d55. GH mRNA was localized in the trophectoderm and syncytium. During the d35-d50 period, concentrations of GH in the maternal circulation were not increased. In umbilical blood, however, GH was detected from d35 and was presumed to be of placental origin, because GH mRNA was not detected in the fetal pituitary gland on d40. We report on GH-R mRNA expression in the placenta between d20-d120. The relative abundance of GH-R transcripts increased significantly between d25-d43. In the endometrium, GH-R mRNA was detected from d8-d120 of pregnancy and from d4-d16 of the cycle. GH-R mRNA was localized in the trophectoderm, fetal mesoderm, and maternal uterine stroma. In the fetal liver, GH-R mRNA was first detectable on d35. The results of this study indicate that between d35-d50 of pregnancy, the endometrium, placenta, and fetus are all potential targets for the placental GH.

Ovine chorionic somatomammotrophin (oCS) production by isolated cotyledon cells from sheep in early and mid gestation: auto-regulation by recombinant oCS

We report the ability of sheep placental cotyledonary cells, isolated at different periods of pregnancy (40 to 90 days) to produce ovine chorionic somatomammotrophin (oCS) in in vitro culture conditions. This oCS production increased gradually with stage of pregnancy. Endogenous oCS net production by isolated placental cells was increased, in a dose-dependent manner, by addition of recombinant oCS (roCS). This effect was not observed after addition of recombinant ovine growth hormone. The roCS effect was more potent on cells collected during early pregnancy. Specific immunoprecipitation of oCS revealed that roCS treatment was associated with an increased dose-dependent incorporation of [35S]methionine-[35S]cysteine. These findings provide evidence that oCS may act in a paracrine/autocrine manner to up-regulate its own production during early gestation. We suggest that this autoregulation may be associated with morphological and functional differentiation of the trophoblast during the growth of the placenta.

Expression of the growth hormone gene in ovine placenta: detection and cellular localization of the protein

In several species, placenta has been found to express GH-related proteins. In the ovine placenta, such a protein, ovine chorionic somatommamotropin, has been described, but its involvement in the fetal/placental growth process is not clearly established. The aim of this study was to investigate the occurrence of another GH-related peptide in the ovine placenta. Placental extracts (days 30-140 of pregnancy) showed GH immunoreactivity between days 35-70. SDS-PAGE analysis of these extracts indicated that this immunoreactivity corresponded to 22- and 28-kDa proteins. GH-like immunoreactivity was localized on cotyledonary frozen sections in the syncytium and the trophectoderm. Northern blot analysis of placental RNA showed the expression of GH-hybridizing transcripts migrating to the same position as that of GH pituitary messenger RNA (mRNA). Those transcripts were highly expressed between days 40 and 50. Their sequence analysis showed the existence of three GH mRNA (GHP1, GHP2, and GHP3). GHP1 is identical to pituitary GH mRNA and probably codes for the 22-kDa protein. GHP2 and GHP3 encode the same protein, which differs from GHP1 by four amino acids. This study establishes the expression of GH gene and GH-immunoreactive proteins in the ovine placenta.

IGF-I and IGF-II receptors in the sheep placenta: evolution during the course of pregnancy

The role of IGFs in placental growth is poorly understood. IGF-II receptors have been characterised in the ovine placenta and used extensively for radioreceptor assay, but their evolution during placental development has not been considered. In this study, binding sites for IGF-I were characterised in the ovine cotyledon by binding and cross-linking studies and the evolution of the number of IGF-I and IGF-II receptors on placentae collected on days 50, 75, 100 and 140 of pregnancy were compared. IGF-I bound onto placental membranes with a mean association constant of 1.7 nM-1 except on day 50 when a lower association constant was observed (0.8 nM-1). Scatchard analysis of the displacement curves led to a single binding site model. IGF-II was as potent as IGF-I at displacing the binding of 125I-labelled IGF-I on those membranes, whereas insulin cross-reaction was only 1%. IGF-II bound on our placental membrane preparations with the characteristics described previously and neither IGF-I nor insulin was able to displace this binding. Affinity cross-linking studies followed by SDS-PAGE under reducing conditions demonstrated that IGF-I was linked to a protein with a molecular weight of about 135,000 Da and IGF-II to a protein of 250,000 Da. The mean +/- S.E.M. number of IGF-I receptors was significantly higher on days 50 and 75 than on days 100 and 140 (154 +/- 12, 105 +/- 11 vs 65 +/- 4, 48 +/- 3 fmol/mg, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

In-vitro secretion of prolactin and growth hormone in the presence of melatonin by pituitary gland from mink kept under long or short days

Mink anterior pituitaries were incubated in Medium 199 for up to 9 or 13 days. Biological activity of prolactin and GH was determined. Daily concentrations of prolactin and GH in the incubation medium were also measured by radioimmunoassay and radioreceptor assay. When females were kept under short days for several weeks before the experiment, a significant decrease in prolactin secretion by the anterior pituitary was observed as compared with that in females maintained under long days. In contrast, secretion of GH was not modified by the photoperiodic history of the animals. Pineal gland denervation by ablation of the superior cervical ganglia a few months before the experiment, or addition of melatonin to the incubation medium of anterior pituitaries from intact or ganglionectomized females, did not modify the secretion of prolactin and GH. The pituitary gland does not therefore seem to be a direct target site for melatonin in transducing the duration of daylength on the hypothalamo-pituitary axis.

Recent data on the structure of rabbit milk protein genes and on the mechanism of the hormonal control of their expression

Mammary explants or isolated mammary cells from rabbit have been cultured in the presence of insulin, prolactin and cortisol alone or in combination. The cellular content in alpha s1-casein, beta-casein and whey acidic protein (WAP) mRNA have been evaluated using the corresponding cDNA as probes. In all cases alpha s1-casein mRNA was the most abundant and WAP mRNA the least abundant mRNA. The three genes showed essentially similar dependency towards hormones. Prolactin stimulated mRNA accumulation and insulin and cortisol amplified this stimulation. The induction by prolactin was rapid whereas stimulation by insulin was slower. Fragments of rabbit genomic DNA inserted in lambda phage and containing alpha s1-casein, and WAP genes have been cloned. The primary sequence around the CAP site of the three genes has been established. A comparison of the sequences located upstream from the CAP site shows several striking homologies with the corresponding genes from cow, rat and guinea-pig. This suggests that these sequences participate in the transcriptional control of the genes by hormones. The mechanism involved in the transduction of the prolactin message to milk protein genes in unknown. Using mammary explants in culture, several classical mechanisms of transduction have been examined. Phorbol ester, phorbol -12, 13-dibutyrate (PdiBu) inhibited prolactin action. However, another tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), did not alter prolactin action. Kinase C inhibitor H7 did not prevent prolactin action and did not overcome the inhibition by PdiBu. Kinase C is therefore not essential for the transduction of the prolactin message to milk protein gene. Neomycin, which inhibits phosphatidylinositol hydrolysis by phosphorylase C, prevented prolactin action, whereas other inhibitors of phosphatidylinositol metabolism remained uneffective. Degradation of phosphatidylinositol is therefore likely not an essential step of prolactin action on milk protein genes. Inhibitors of tyrosine kinase and phosphatase exhibited a poor capacity to modify the prolactin response. Hence, transduction mechanisms using tyrosine kinase activity likely cannot account for prolactin action.

Effect of tubulozole, a new synthetic microtubule inhibitor, on the induction of casein gene expression by prolactin

Colchicine and related drugs are known to inhibit milk secretion. They are also able to prevent stimulation of casein and DNA synthesis by prolactin in the mammary gland. The present report reports data obtained with tubulozole, a new antimitotic drug. Tubulozole C added to culture medium of isolated rabbit epithelial mammary cells strongly inhibited their multiplication. Simultaneously, at a concentration of 1 microM, it prevented almost completely the induction of beta-casein mRNA. Induced cells were rapidly deinduced by addition of the drug to the medium. A similar inhibition was observed when the induction was obtained with prolactin alone or with its two stimulators insulin and glucocorticoids. Tubulozole T, an isomer of tubulozole C which is known to be ineffective in disrupting microtubules, did not alter prolactin actions. These data and those obtained with other tubulin-binding drugs strongly suggest that the integrity of microtubules is required for prolactin to deliver its message to the mammary cell.

Hormonal action controlling mammary activity

Mammary gland differentiation includes multiplication of cells, activation of genes specific to milk synthesis, and activation of "house-keeping" genes. These events are controlled by multiple hormones, the roles of which are not known in detail. Prolactin induction of milk synthesis is accompanied by accumulation of casein messenger ribonucleic acid resulting from acceleration of casein gene transcription as well as stabilization of messenger ribonucleic acid. Prolactin also favors translation of casein messenger ribonucleic acid. Glucocorticoids amplify and progesterone inhibits prolactin action on transcription of casein genes.

Comparative measurement of the lactogenic activity of ovine placental lactogen in rabbit and ewe mammary gland

Ovine placental lactogen is known to bind to prolactin receptors and to initiate milk synthesis in the rabbit mammary gland. However, this hormone exhibited a very low capacity of competing with 125I-labeled human growth hormone for the binding to membranes extracted from ewe mammary gland. Ovine placental lactogen was very efficient in provoking the accumulation of beta-casein mRNA in rabbit mammary explants but was much less active on ewe mammary explants. These data indicate that the placental hormone is not a potent lactogen in the homologous species and that its role in the control of mammary gland development and activity may have been previously overestimated.