DIFFERENTIAL REGULATION OF LEUCINE-RICH PRIMARY RESPONSE GENE-1 (LRPR1) MESSENGER-RNA EXPRESSION IN RAT TESTIS AND OVARY

In immature rat Sertoli cells, leucine-rich primary response gene 1 (L RPR1) represents a follicle stimulating hormone (FSH)-responsive gene; the function of the encoded protein is not yet known. LRPR1 mRNA expr ession is up-regulated very rapidly and specifically by FSH, both in c ultured Sertoli cells and in vivo in testicular tissue. In view of the se properties of LRPR1, we have investigated LRPR1 mRNA expression and its regulation in more detail, in testis and ovary of fetal, immature , and adult rats. In addition, we have studied the expression of FSH r eceptor (FSHR) mRNA in relation to LRPR1 mRNA expression. In rat testi s, LRPR1 mRNA and FSHR mRNA followed a similar expression pattern, dur ing postnatal development and also at different stages of the spermato genic cycle in the adult rat. Furthermore, after short-term challenge of the FSH signal transduction pathway in intact immature rats by inje ction with a relatively high dose of FSH, an inverse relationship betw een LRPR1 mRNA (up-regulation) and FSHR mRNA expression (down-regulati on) was observed. Similar studies in the ovary provided completely dif ferent results. LRPR1 mRNA in the postnatal ovary is present well befo re expression of FSHR mRNA can be first detected. In addition, incubat ion of ovaries of immature rats with FSH or dibutyryl cyclic BMP (dbcA MP) did not result in up-regulation of LRPR1 mRNA expression. During f etal development, the LRPR1 mRNA expression pattern involved many more tissues, in contrast to the relatively tissue-specific expression of LRPR1 mRNA in gonads of 21 day old and adult rats. Moreover, LRPR1 mRN A expression could be detected as early as 12.5 days post-coitum, wher eas FSHR mRNA is absent at this stage of fetal development. We conclud ed that the pronounced regulation of LRPR1 by FSH observed in the imma ture rat testis does not occur in the ovary. Furthermore, in the ovary LRPR1 mRNA expression does not appear to be dependent on FSH action. Finally, the LRPR1 gene product may play a general role during fetal d evelopment.