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Role of Central Nervous System and Ovarian Insulin Receptor Substrate 2 Signaling in Female Reproductive Function in the Mouse¹

Centre for Diabetes and Endocrinology,³ Rayne Institute, University College London, London WC1E 6JJ, United Kingdom Department of Metabolic Medicine,⁴ and Institute of Reproductive and Developmental Biology,⁵ Imperial College London, London W12 0NN, United Kingdom

ABSTRACT

Insulin receptor signaling regulates female reproductive function acting in the central nervous system and ovary. Female mice that globally lack insulin receptor substrate (IRS) 2, which is a key mediator of insulin receptor action, are infertile with defects in hypothalamic and ovarian functions. To unravel the tissue-specific roles of IRS2, we examined reproductive function in female mice that lack Irs2 only in the neurons. Surprisingly, these animals had minimal defects in pituitary and ovarian hormone levels, ovarian anatomy and function, and breeding performance, which indicates that the central nervous system IRS2 is not an obligatory signaling component for the regulation of reproductive function. Therefore, we undertook a detailed analysis of ovarian function in a novel Irs2 global null mouse line. Comparative morphometric analysis showed reduced follicle size, increased numbers of atretic follicles, as well as impaired oocyte growth and antral cavity development in Irs2 null ovaries. Granulosa cell proliferation was also defective in the Irs2 null ovaries. Furthermore, the insulin- and eCG-stimulated phosphoinositide-3-OH kinase signaling events, which included phosphorylation of Akt/protein kinase B and glycogen synthase kinase 3-beta, were impaired, whereas mitogen-activated protein kinase signaling was preserved in Irs2 null ovaries. These abnormalities were associated with reduced expression of cyclin D2 and increased CDKN1B levels, which indicates dysregulation of key components of the cell cycle apparatus implicated in ovarian function. Our data suggest that ovarian rather than central nervous system IRS2 signaling is important in the regulation of female reproductive function.

insulin, insulin-like growth factor receptor, kinases, oocyte development, ovary

¹Supported by an MRC Co-operative Component Grant and a Wellcome Trust Functional Genomics Award.

Correspondence: ²Dominic J. Withers, Centre for Diabetes and Endocrinology, Rayne Institute, 5 University Street, University College London, London WC1E 6JJ, United Kingdom. FAX: 4420 767 96583; e-mail: d.withers{at}ucl.ac.uk

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