![]() ![]() Significant conceptus loss occurs during trophectoderm elongation between gestational day 11 ( D11) and day 12 ( D12). Elongation of the porcine conceptus is a key stage of development during which maternal recognition of pregnancy, initial placental development, and preparation for implantation occurs. The objective of this study was to establish comparative transcriptome profiles of D11 ovoid and D12 filamentous conceptuses and thereby identify temporally regulated genes essential for developmental progression during conceptus elongation. Serial analysis of gene expression (SAGE) libraries were constructed from in vivo derived ovoid and filamentous swine conceptuses to yield a total of 42,389 tags (ovoid) and 42,391 tags (filamentous) representing 14,464 and 13,098 putative unique transcripts, respectively. Statistical analysis of tag frequencies revealed the differential expression of 431 tags between libraries ( P < 0.05). Nucleotide sequence alignment searches on public databases provided SAGE tag annotation and gene ontology assignments. Comparisons between the SAGE profiles of ovoid and filamentous conceptuses revealed increased expression of key genes in the steroidogenesis and oxidative stress response pathways. Differential expression of these genes in the steroidogenic and oxidative stress response pathways was confirmed by real-time PCR. These results validate the utility of SAGE in the pig and establish an initial model linking gene expression profiles at the pathway level with phenotypic progression from ovoid to filamentous stages of conceptus development. Swine often exhibit high rates (∼18%) of preimplantation conceptus mortality following either artificial insemination or natural mating ( 6). The major conceptus loss occurs prior to gestational day 20 ( D20) however, the most critical period spans gestational day 11 ( D11) to day 12 ( D12) when the conceptus undergoes a dramatic morphological change ( 15). ![]() Moreover, the efficiencies of producing swine conceptuses in vitro are poor compared with other livestock species. Approximately 20% of in vitro produced swine conceptuses develop into live offspring after transfer to recipient gilts ( 1). Porcine conceptuses develop through a series of four critical transitional stages prior to implantation. Development from the two- to four-cell stages, day 2 ( D2) after insemination, coincides with the transition from maternal to embryonic genome expression within the conceptus ( 39). Morphological differentiation and cellular polarization occur within the blastocyst stage conceptus at day 6 ( D6) after insemination ( 26, 32). The blastocyst also represents the stage most commonly transferred or cryopreserved in swine ( 11). Beginning at D11, porcine conceptuses undergo dramatic elongation from an 8–10 mm ovoid to a >150-mm filament by D12 ( 15). The phenomenon of conceptus elongation also occurs in the sheep and cow at D11 and day 13 ( D13), respectively ( 5). This morphological change occurs via hyperplasia in the sheep and cow, whereas in the pig the initial stages of trophectoderm elongation take place through cellular reorganization and differentiation, and proliferation is a later event ( 15, 30). Asynchrony in the timing of elongation among D11 and D12 swine conceptuses in utero may play an important role in conceptus survival blastocysts differentiating earlier may have a competitive edge over their lagging cohorts in obtaining the uterine surface necessary for further development ( 5). Coinciding with elongation, D12 swine conceptuses also synthesize and secrete estrogens that serve as an important molecular signal in establishing the maternal recognition of pregnancy ( 16, 30). Spatial and temporal patterns of gene expression are highly orchestrated during preimplantation conceptus development. Studies utilizing semiquantitative PCR analyses, suppressive subtractive hybridization (SSH), RNA arbitrarily primed-PCR (RAP-PCR), or expressed sequence tags (EST) have identified transcripts that have important physiological roles during trophectoderm elongation ( 34, 35, 41– 43). For example, transcripts for steroidogenic enzymes CYP19A and 17α-hydroxylase ( CYP17A1) were upregulated between gestational D11 and D12, a pattern consistent with increased estrogen synthesis ( 30, 43). ![]()
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