Differentiation of the granulosa layer from hen prehierarchal follicles associated with follicle‐stimulating hormone receptor signaling

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Abstract
Recruitment of a single follicle into the preovulatory hierarchy of the domestic hen ovary occurs from a small cohort of prehierarchal follicles measuring 6–8 mm in diameter. We have previously reported that granulosa cells (GCs) collected from prehierarchal follicles express highest levels of membrane‐localized follicle‐stimulating hormone receptor (FSHR) during follicle development, yet fail to initiate signaling via cAMP following short‐term incubation with FSH. Consequently, GC from prehierarchal follicles remain in an undifferentiated state and lack the capacity for steroidogenesis due to a deficiency of cAMP‐dependent STAR protein and CYP11A1 gene expression. The present studies investigate FSH responsiveness in GC before and after the transition from undifferentiated to a differentiated state at follicle recruitment. Before recruitment focus is directed toward the inhibition of FSHR‐signaling by β‐ARRESTIN (βARR). Specifically, knockdown of βARR messenger RNA in cultured, undifferentiated GC using small interfering RNA facilitated FSH‐induced cAMP formation, STAR expression, and progesterone production. Furthermore, overexpression of bovine βARR1 and G‐protein‐coupled receptor kinase2 in actively differentiating GC significantly decreased cAMP accumulation and progesterone production following a challenge with FSH. We propose that a βARR‐mediated mechanism maintains FSHR unresponsiveness in undifferentiated GC from prehierarchal follicles, and as a result prevents GC differentiation until the time of follicle recruitment.
Funding Information
  • National Science Foundation (IOS‐1354713)

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