Differences in the expression of cytochromes P450 17 alpha-hydroxylase and aromatase in Meishan and Yorkshire conceptuses at days 10.5-14.0 of gestation

Comparative proteomic and regulatory network analyses of the elongating pig conceptus

Embryo loss during peri-implantation can approach 20% in swine following artificial insemination or natural mating and coincides with rapid conceptus elongation. The objective of the present study was to establish a comprehensive profile of the abundant proteins of the pig conceptus at the time prior to implantation and identify stage-specific changes during elongation. The abundant proteins of a homogenous population of gestational day-11 ovoid (0.7-1 cm) and gestational day-12 filamentous (15-20 cm) porcine concepti were compared by extracting proteins from three independent conceptus pools and separating the proteins by 2-DE. Proteins in 305 spots were analyzed by MALDI-TOF or additionally by LC-MS/MS and 275 were positively identified representing 174 distinct proteins. The proteins could be classified into the following functional categories: cell proliferation/differentiation, cytoskeleton, metabolism, and stress response. Based on spot density, 35 proteins associated with cell proliferation, differentiation, apoptosis, and embryo/maternal signaling, were found to be differentially expressed between ovoid and filamentous concepti. A comparison of the protein expression profile with transcriptomic data from pig concepti of the same developmental stages identified similarities and dissimilarities between protein and mRNA expression profiles. This proteomic study helps to elucidate the biological mechanisms underlying the early embryonic development of the pig.

Isolation of differentially expressed genes in conceptuses and endometrial tissue of sows in early gestation

The implantation period is a critical time for embryonic survival in pigs. During this period, numerous growth factors are secreted by the conceptuses and the uterine endometrium in order to establish pregnancy and to provide a proper environment for embryonic development. It is well known that the Chinese Meishan sows have a larger litter size when compared with occidental sows mainly because of a superior embryonic survival rate. As a further step toward understanding the mechanisms involved in embryonic survival, we used a suppression subtractive hybridization technique to identify genes that were differentially expressed in Meishan-Landrace conceptuses and endometrial tissue at Day 15 of gestation when compared with conventional Landrace sows. Of the 1000 subtractive clones isolated from each library, 137 endometrial and 166 conceptus-enriched cDNAs were single-pass sequenced and examined by BLAST analysis for identification. Sixty-two percent of the clones found in the endometrial library and 78% of the clones found in the conceptus library showed homology with known genes. Among these genes, the 20 most relevant to embryonic survival based on the available literature were validated through real-time reverse-transcriptase polymerase chain reaction (RT-PCR) analysis. Our results show that suppression subtractive hybridization is a powerful method applicable in identifying putative candidate genes that might be used for selection of high litter-size breeds.

EST-based gene discovery in pig: virtual expression patterns and comparative mapping to human

A molecular understanding of porcine reproduction is of biological interest and economic importance. Our Midwest Consortium has produced cDNA libraries containing the majority of genes expressed in major female reproductive tissues, and we have deposited into public databases 21,499 expressed sequence tag (EST) gene sequences from the 3' end of clones from these libraries. These sequences represent 10,574 different genes, based on sequence comparison among these data, and comparison with existing porcine ESTs and genes indicate as many as 4652 of these EST clusters are novel. In silico analysis identified sequences that are expressed in specific pig tissues or organs and confirmed the broad expression in pig for many genes ubiquitously expressed in human tissues. Furthermore, we have developed computer software to identify sequence similarity of these pig genes with their human counterparts, and to extract the mapping information of these human homologues from genome databases. We demonstrate the utility of this software for comparative mapping by localizing 61 genes on the porcine physical map for Chromosomes (Chrs) 5, 10, and 14.

Synchronous onset of oestradiol-17beta secretion by Meishan conceptuses

The response of Meishan conceptuses to an exogenous precursor for oestradiol-17beta biosynthesis was investigated in vitro, to determine whether gestational age or morphological stage of development elicit changes in hormone metabolism. Conceptuses were recovered on days 11, 12, 13 or 15 after the onset of oestrus and cultured for 6 hours at 37 degrees C, in the presence or absence of testosterone. On days 12 and 13 after the onset of oestrus spherical conceptuses were recovered from some gilts, whereas others yielded elongated or filamentous conceptuses. All conceptuses recovered on day 15 after oestrus had elongated. The number of cells per individual conceptus increased from days 11 to 13 after the onset of oestrus (P < 0.001), as did conceptus surface area (P = 0.038). Supplementing culture media with testosterone, as a substrate for oestrogen biosynthesis, significantly increased conceptus oestradiol-17beta secretion in vitro on days 12, 13 and 15, regardless of whether pre- or post-elongation conceptuses were cultured. However, on day 11 oestradiol-17beta was only detected at significant concentrations in the culture media of four testosterone supplemented conceptuses and only one gilt produced conceptuses capable of secreting oestradiol-17beta in the absence of testosterone. Therefore, the onset of conceptus oestradiol-17beta secretion is apparently limited by the expression of aromatase enzymes that are activated synchronously, irrespective of the stage of morphological development, within Meishan litters. Once established, Meishan conceptus oestradiol-17beta secretion in vitro is increased in the presence of exogenous testosterone.

Molecular cloning of porcine estrogen receptor-beta complementary DNAs and developmental expression in periimplantation embryos

In the pig, estrogens transiently produced by embryos and progestins of maternal origin target the uterine endometrium, causing alterations in gene expression and secretory activity, both of which are important for the initiation of embryo attachment. The potential direct embryotrophic roles of estrogens and progestins are, however, unknown. Here we report the cloning of porcine embryonic estrogen receptor-beta (ER-beta) mRNA by reverse transcription-polymerase chain reaction (RT-PCR) using specific primer sets designed initially within conserved regions of human and bovine ER-beta mRNAs, and subsequently within regions of identified porcine ER-beta cDNA sequences. The ER-beta mRNA has an open reading frame of 1578 nucleotides and encodes a 526 amino acid polypeptide that displays greater than 90% identity with other mammalian ER-beta proteins. Northern and Western blot analyses using porcine filamentous embryos from Day 12 of pregnancy demonstrated the presence of multiple ER-beta mRNA transcripts of approximately 9.5, 4.9, and 3.5 kilobases, and a similar 64-kDa protein corresponding in size to human ovarian granulosa cell ER-beta, respectively. In Day 12 filamentous embryos, ER-beta expression was immunolocalized to trophoblastic cell nuclei, coincident with that of proliferative cell nuclear antigen (PCNA). The developmental ontogeny of ER-beta mRNA was evaluated in embryos of different morphologies (spherical, tubular, and filamentous) by semiquantitative RT-PCR, along with those for other steroid hormone receptors (ER-alpha and progesterone receptor) and known embryonic genes associated with cell differentiation (cytochrome P450 aromatase type III) and growth (cyclin D1). ER-beta mRNA levels varied with embryo morphology (filamentous maximum at Day 12), coincident with that of cyclin D1. Progesterone receptor mRNA levels were maximal in tubular embryos, similar to that of P450 aromatase, whereas the expression of the ER-alpha gene was barely detectable and appeared constitutive for all developmental stages examined. Estradiol-17 beta treatment of Day 12 filamentous embryos in culture up-regulated ER-beta and P450 aromatase (type III) mRNA levels, respectively, but decreased those of PCNA, and had no effect on cyclin D1 mRNA levels. These studies taken together suggest that embryonic ER-beta likely mediates the autocrine functions of estrogens in the dynamic regulation of embryonic growth and development at periimplantation.

Development and differentiation of the interstitial and tubular compartments of fetal porcine testes

Male differentiation is initiated by fetal testicular androgen synthesis, catalyzed by the enzyme 17alpha-hydroxylase/17,20 lyase cytochrome P450 (P450c17). This study was an investigation of testicular development and differentiation in porcine fetuses recovered on Days 30-42 of gestation. The expression of P450c17 was localized in fetal gonads by in situ hybridization and immunocytochemistry and related to cellular proliferation through expression of the proliferating cell nuclear antigen (PCNA). Gonadal P450c17 expression was quantified by Western immunoblot analysis and related to testosterone secretion by cultured explants of fetal gonads. P450c17 transcripts were detected in the interstitium surrounding testicular cords preceding the appearance of the enzyme protein. The intensity of both P450c17 hybridization and staining was greater in Yorkshire fetal gonads, which also exhibited more advanced tubular development. PCNA staining was prominent within tubular primordia and was higher in testes from Yorkshire than from Meishan fetuses on all days examined. P450c17 expression paralleled testosterone secretion, which decreased by Day 42, and was generally less in cultures of Meishan than of Yorkshire fetal gonads. These data demonstrate that the expression of P450c17 in porcine fetal testes coincides with differentiation of central medullary cells and androgen secretion during gonadal development between Days 30 and 42 of gestation. This occurs as medullary cords organize and is associated with changes in cellular proliferation within the tubular compartment.