EXPRESSION ANALYSIS OF THE STEROIDOGENIC ACUTE REGULATORY PROTEIN (STAR) GENE IN DEVELOPING PORCINE CONCEPTUSES

Authors: Blomberg, Le Ann; Zuelke, Kurt

Submitted to: Journal of Molecular Reproduction and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2005
Publication Date: 12/10/2005
Citation: Blomberg, L., Zuelke, K.A. 2005. Expression analysis of the steroidogenic acute regulatory protein (STAR) gene in developing porcine conceptuses. Journal of Molecular Reproduction and Development. 72:419-429.

Interpretive Summary: Temporally precise patterning of steroid hormone synthesis and secretion plays a fundamental role in assuring normal conceptus development and gestation in swine. The aim of the present study was to establish a potential mechanistic role for Steroidogenic Acute Regulatory Protein (STAR) in cholesterol transport and steroidogenesis in the pig conceptus prior to implantation. We confirmed the presence and differential expression of a novel STAR mRNA transcript, LF STAR, in the porcine conceptus. The presence of LF STAR mRNA and its differential expression during porcine conceptus elongation confirm and extend the results of previous Serial Analysis of Gene Expression (SAGE) comparisons between ovoid and filamentous porcine conceptuses. Differential expression of STAR was concomitant with an increase in the stimulatory transcription factor steroidogenic factor 1 (SF-1), and decrease in the inhibitory transcription factor dosage-sensitive sex reversal, adrenal hypoplasia congenital, critical region on the X chromosome, gene-1 (DAX-1), transcript level. In comparison with mRNA data, Western blot analyses demonstrated similar levels of STAR protein expression in D11 ovoid and D12 filamentous conceptuses. These data confirm the presence of STAR mRNA and protein levels in elongating porcine conceptuses, and suggest temporal expression of STAR mRNA during elongation may be modulated, in part, through differential regulation of SF-1 and DAX-1.

Technical Abstract: Steroidogenesis in porcine non-conceptus tissue is regulated by the STAR-dependent transport of cholesterol from the outer to inner mitochondrial membrane. Previous Serial Analysis of Gene Expression (SAGE) identified a STAR mRNA transcript in the porcine peri-implantation conceptus during trophectoderm elongation and increased conceptus estrogen synthesis between gestational day (D) 11 and D12. To assess a potential mechanistic role for STAR in the modulation of conceptus steroidogenesis via cholesterol transport, the conceptus STAR transcript was PCR cloned and temporal expression of mRNA and protein were examined. The conceptus variant represented a longer transcript (LF STAR; ~ 2.5 kb) with 99% similarity to a truncated ovarian STAR transcript (SF STAR; GenBank Acc. No. U53020). Northern analysis of D12 corpora lutea and pig conceptus RNA identified multiple STAR transcripts in both tissues. The LF STAR transcript was temporally regulated; displaying negligible, maximal, and intermediate levels in blastocyst stage, filamentous D12 and D25 conceptuses, respectively. Differential expression of STAR was concomitant with an increase in the stimulatory transcription factor steroidogenic factor 1 (SF-1), and decrease in the inhibitory transcription factor dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene-1 (DAX-1), transcript level. In comparison with mRNA data, Western blot analyses demonstrated similar levels of STAR protein expression in D11 ovoid and D12 filamentous conceptuses. These data confirm the presence of STAR mRNA and protein levels in elongating porcine conceptuses, and suggest temporal expression of STAR mRNA during elongation may be modulated, in part, through differential regulation of SF-1 and DAX-1.