Tyrosine phosphorylation of STAT3 by leptin through leptin receptor in mouse metaphase 2 stage oocyte

Leptin is the product of the obese gene (ob), and is secreted in plasma fro m mature adipocytes. It has been recently reported that leptin is synthesiz ed in granulosa and cumulus cells within the follicle of the ovary, and is present in mature human oocytes, suggesting possible roles of leptin in sev eral aspects of pre- and post-ovulatory follicular development. On the othe r hand, TAT (Signal Transducer and Activator of Transcription) transcriptio n factors are involved in leptin-associated signal transduction. In this re port, we studied the expression of leptin receptor and STAT3 activation by leptin in metaphase 2 stage (M2) oocytes. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblotting showed that mRNA and protein of leptin receptor were expressed in M2 stage oocyte. Leptin at 15 ng/ml, the concentration observed in follicular fluid, caused tyrosine phosphorylation of STAT3 in mouse M2 stage oocytes. These results suggest possible roles o f leptin in several aspects during oocyte maturation by activating the STAT signal transduction pathway. (C) 1999 Academic Press.