ONTOGENY OF LH AND FSH RECEPTORS IN POSTNATAL RABBIT TESTES - AGE-DEPENDENT DIFFERENTIAL EXPRESSION OF LONG AND SHORT RNA TRANSCRIPTS

The ontogeny of testicular LH and FSH receptors was studied in New Zea land rabbits from 20 to 180 days postpartum. The concentrations of fre e receptors (per mg total proteins) were very low at day 20. They incr eased steeply at day 30 for the LH receptor and at day 50 for the FSH receptor. Three RNA bands (1.2, 2.5 and 3 kb) were repeatedly detected on northern blots for the LH receptor and two bands (1.2 and 2.2 kb) were detected for the FSH receptor. The 1.2 kb band (which cannot give rise to full-length, membrane-anchored receptor) was present througho ut the 20-180 day period for each receptor. However, the higher molecu lar mass bands were nearly undetectable at day 20. The 2.5 and 3 kb ba nds of the LH receptor increased twofold between day 20 and day 120, w hile the 2.2 kb band of the FSH receptor increased fivefold between da y 20 and day 75. Thus the very low concentrations, or even absence, of the larger transcripts of both LH and FSH receptors were correlated w ith the inability to detect their cognate protein until 20 days of age . Subsequently, coordinated increases in high molecular mass transcrip ts and protein were observed for both receptors. Total LH receptor con tent increased in parallel to the previously reported increase in plas ma testosterone between day 65 and day 100. FSH receptor density began to increase steeply at day 50, just at the onset of spermatogenesis. Thus, postnatal testicular development in the rabbit seems to entail t he transcription of high molecular mass, translatable transcripts oi: the gonadotrophin receptors.