Ontogenesis 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 Zealand rabbits from 20 to 180 days postpartum. The concentrations of free receptors (per mg total proteins) were very low at day 20. They increased 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 throughout the 20-180 day period for each receptor. However, the higher molecular mass bands were nearly undetectable at day 20. The 2.5 and 3 kb bands of the LH receptor increased twofold between day 20 and day 120, while the 2.2 kb band of the FSH receptor increased fivefold between day 20 and day 75. Thus the very low concentrations, or even absence, of the larger transcripts of both LH and FSH receptors were correlated with the inability to detect their cognate protein until 20 days of age. Subsequently, coordinated increases in high molecular mass transcripts and protein were observed for both receptors. Total LH receptor content increased in parallel to the previously reported increase in plasma 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 the transcription of high molecular mass, translatable transcripts of the gonadotrophin receptors.