Δ5–4 isomerase messenger ribonucleic acids and steroidogenesis during pubertal development in the rat testis (original) (raw)

2000, The Journal of Steroid Biochemistry and Molecular Biology

Changes in expression of Leydig cell 3b-hydroxysteroid dehydrogenase (3bHSD) and 17a-hydroxylase/C17±20 lyase (P450 17a ) messenger RNA (mRNA) during pubertal development have not been well characterized in the rat. In the present study, expression of 3bHSD and P450 17a were determined in frozen sections of testes of immature (days 21 and 28), pubertal (days 45 and 60) and adult (day 90) rats by in situ hybridization using digoxigenin-labeled riboprobes and quanti®ed densitometrically. Measures of steroidogenesis in this study, 3bHSD and P450 17a enzyme activities per testis and plasma testosterone concentration, increased during pubertal development, peaking at 45±60 days of age. Expression of 3bHSD protein, a marker for Leydig cell function, was abundantly immunolocalized to the interstitial compartment of the testis. Quanti®ed densitometrically, the amount of 3bHSD protein did not vary signi®cantly during pubertal development. Transcripts of 3bHSD and P450 17a were expressed abundantly by clusters of immature Leydig cells in immature animals. However, in contrast to measures of steroidogenesis during pubertal development, mRNA of 3bHSD and P450 17a decreased to undetectable levels at the age of 45 and 60 days, respectively. The decline in mRNA of 3bHSD and P450 17a was con®rmed by Northern analysis. Expression of 3bHSD and P450 17a transcripts rebounded in the adult at 90 days and were comparable to levels of expression observed in immature animals. These results show that during pubertal development the steady-state accumulation of mRNA of 3bHSD and P450 17a are not correlated with accumulation of 3bHSD protein, enzyme activities of 3bHSD and P450 17a , or testosterone secretion. Possible explanations of the depletion of transcripts during pubertal development include: speci®c inhibition of transcription, increased mRNA instability, or high translational activity. 7