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Reproduction (2005) 129 453-461
DOI: 10.1530/rep.1.00464
Copyright © 2005 Society for Reproduction and Fertility
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RESEARCH

Gene expression for LH receptor, 17{alpha}-hydroxylase and StAR in the theca interna of preantral and early antral follicles in the bovine ovary

R Braw-Tal1 and Z Roth2

1 Agricultural Research Organization, the Volcani Center, Institute of Animal Science, Bet Dagan 50250, Israel and 2 Faculty of Agriculture, Department of Animal Science, The Hebrew University of Jerusalem, Rehovot, Israel

Correspondence should be addressed to R Braw-Tal; Email: brawtal{at}agri.huji.ac.il

The onset of gene expression for three proteins that play pivotal roles in theca interna function, namely the LH receptor (LH-R), cytochrome P450 17{alpha}-hydroxylase (17{alpha}OH) and the steroidogenic acute regulatory protein (StAR), was determined. Ovaries were obtained on day 9 of the oestrus cycle from mature synchronized dairy cows (n = 5) and gene expression in preantral and antral follicles up to 4 mm in diameter was evaluated by in situ hybridization. LH-R and 17{alpha}OH mRNAs were observed first, in the theca interna of large preantral follicles (type 4), concurrent with its morphological differentiation. StAR mRNA appeared later during follicular growth, in follicles >1 mm in diameter (type 6). LH-R and 17{alpha}OH mRNAs were found exclusively in the thecal cells, whereas StAR mRNA appeared in thecal cells, granulosa cells of late atretic follicles and oocytes. In early atresia, thecal cells expressed all three mRNAs, and their expression decreased gradually as atresia progressed. Atresia in granulosa cells was characterized by massive apoptosis of periantral, but not peribasal cells, that differentiated into luteal-like cells expressing StAR.

In summary, our study suggests that in spite of the presence of 17{alpha}OH, a key enzyme in steroidogenesis, the ability to produce steroids by bovine follicles smaller than 1 mm in diameter must be very limited due to the absence of StAR protein. During the early stages of atresia, thecal cells remain morphologically and functionally healthy, and continue to express all three studied mRNAs.




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