Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2004
Publication Date: August 1, 2004
Citation: Blomberg, L., Dobrinsky, J.R., Zuelke, K.A. 2004. Steroidogenic acute regulatory protein (star) gene expression coincides with increased estrogen synthesis in porcine embryos [abstract]. 37th Annual Meeting of the Society for the Study of Reproduction. p. 213.
STAR-mediated transport of cholesterol to the inner mitochondrial membrane regulates steroidogenesis in porcine adrenal and gonadal tissue. Steroid production, crucial for implantation, also occurs in the porcine preimplantation embryo during trophectoderm elongation between gestational day (D) 11 and D12, however, the mechanism for the intracellular transport of cholesterol in the pig embryo is unknown. Serial analysis of gene expression (SAGE) detected a novel STAR mRNA transcript that was present in D11 (elliptical; ~10 mm) and upregulated in D12 (filamentous; ~150 mm) embryos. The objective of this study was to clone the embryonic STAR cDNA, determine its temporal expression pattern during preimplantation development, and characterize its expression at the protein level. Total RNA was isolated from D12 filamentous embryos and, via PCR, a composite sequence of ~ 2.4 kb representing a long form (LF) STAR transcript was generated. The open reading frame (ORF) nucleotide sequence of the embryonic STAR cDNA had a similarity of 99% to a short form (SF), ovarian STAR transcript (U53020). However, the LF clone contained an additional 1317 bp in the 3' untranslated region (UTR) that was not present in the SF STAR sequence. Northern blot analysis of D12 corpora lutea, D11 embryo, and D12 embryo RNA detected transcripts of 2.9 kb, 1.8 kb and 1.7 kb in all tissues; the 2.9 kb transcript was the most abundant in each tissue. RT-PCR analysis revealed that the relative expression of STAR mRNA was negligible in D6 blastocyst stage embryos, maximal in D11 and D12 during elongation, and markedly decreased by D25 of development. Western blot analysis confirmed that the STAR protein was expressed in embryos. In contrast to STAR expression at the mRNA level, there was no evidence of differential of STAR protein expression between D11 and D12 embryos. Combined, the present data demonstrating that STAR expression at the mRNA and protein levels indicates that STAR may likely function as the cholesterol transporter within embryonic mitochondria and could thereby be a major regulator of steroidogenesis during pig embryo elongation.