RHOX Homeobox Transcription Factor Regulation of Ins2 in Rodent Granulosa Cells

Area of Science:

• Reproductive biology
• Molecular endocrinology
• Genetics

Background:

• The Rhox family of homeobox transcription factors are key regulators of gonad function.
• Downstream targets of Rhox factors, especially in the female reproductive tract, remain largely unknown.

Purpose of the Study:

• To identify and characterize downstream targets of Rhox5 and Rhox8 in the female reproductive tract.
• To investigate the role of Ins2 as a novel target gene regulated by Rhox5 and Rhox8 in ovarian granulosa cells.

Main Methods:

• Gene expression analysis of Ins2 in wild-type and Rhox5-null mice.
• Reporter assays to assess Ins2 promoter activity in response to Rhox8.
• In vivo knockdown of Rhox8 in granulosa cells to evaluate its role in Ins2 regulation.

Main Results:

• Insulin 2 (Ins2) gene expression was detected in mural granulosa cells of large antral follicles, independent of Rhox5.
• Rhox8 was identified as the major regulator of Ins2 expression in granulosa cells, confirmed by reporter assays and in vivo knockdown.
• Rhox5 induces Rhox8 expression in early follicular development, while Rhox8 expression peaks post-LH surge, potentially mediated by progesterone.

Conclusions:

• Insulin 2 (Ins2) is a novel downstream target of Rhox8 in ovarian granulosa cells.
• Rhox8 plays a critical role in regulating Ins2 expression, particularly in later stages of follicular development.
• The interplay between Rhox5, Rhox8, and progesterone may explain the normal fertility observed in Rhox5-null female mice, highlighting functional redundancy in ovulation regulation.