Abstract
Differential regulation of LHR in theca cells (TC) and granulosa cells (GC) is important for normal follicular development. Unlike TC, GC only acquire LH-responsiveness during the later stages of antral follicle development. This study tested the hypothesis that differential LH-responsiveness in these two cell types may be due, in part, to shifts in cellular patterns of alternatively spliced LHR mRNA transcripts which may not be obvious from analysis of total LHR gene expression. It also further explored the role of translation inhibition by an LHR binding protein (LHBP), normally associated with the production of endogenous cholesterol. LHR mRNA variation arises as a result of the alternative splicing of two variable deletion sites (VDS) designated 5′ VDS and 3′ VDS, and it was proposed that differences in cell sensitivity to LH may be due in part to variations in the pattern of the mRNA expression of the receptor variants. The outcomes of the present study support a dynamic multi-facetted regulation of LHR during pre-translation. Not only did the ratio between variants change during antral follicle growth and in vitro cell differentiation but also between TC and GC. Regulation could also be linked to LH concentration feedback mechanisms as the absence of LH caused cultured TC to markedly up-regulate amounts of LHR mRNA. In both TC and GC, LHR mRNA was greatly reduced after treatment to block mevalonate production in the de novo cholesterol pathway, adding further support for a regulatory mechanism linked to enriched cellular amounts of mevalonate kinase.
Highlights
The pituitary gonadotrophins, luteinising hormone (LH) and follicle stimulating hormone (FSH) signal via specific membrane bound receptors
Using a PCR primer set which targeted all LHR splice variants (LHR.ex7.F/LHR.ex9.R; Table 1 and Fig. 1a and b) to determine the relative amounts of LHR mRNA in theca cells (TC) and granulosa cells (GC) taken from various sized follicles it was found (Fig. 1c) that there were marked differences between the two cell types, with relative amounts of LHR mRNA in TC from follicles in the 1–2 mm, 3–5 mm, 6–10 mm and >10 mm pools being greater than in GC from the same sized follicles
When the primer pair LHR.ex1.F/LHR.ex8.R was used, in TC of cattle cultured over time, to amplify LHR mRNA isoforms having the 5 variable deletion sites (VDS) (Fig. 1b), the same two 5 VDS splice variations were detected as in cells taken from various sized antral follicles
Summary
The pituitary gonadotrophins, luteinising hormone (LH) and follicle stimulating hormone (FSH) signal via specific membrane bound receptors. FSH receptors occur exclusively on the GC of ovarian follicles from primary through to. P. Marsters et al / Animal Reproduction Science 163 (2015) 63–74. FSH-responsiveness (Campbell and Baird, 2001). LH receptors play a critical role in supporting progesterone secretion by the corpus luteum (Niswender, 2002). The responsiveness of follicular somatic cells to LH has attracted a great deal of research interest. The mechanisms underlying regulation of its cellular responses still remain relatively poorly understood
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