PROENKEPHALIN GENE-EXPRESSION IN TESTICULAR INTERSTITIAL-CELLS IS DOWN-REGULATED COINCIDENT WITH THE APPEARANCE OF PACHYTENE SPERMATOCYTES

Two distinct forms of proenkephalin messenger RNA (mRNA) are present i n the murine testis, a family of 1.7 kilobases (kb), germ cell-specifi c transcripts and a 1.45-kb form that is also found in somatic tissues . In situ hybridization and molecular analysis of purified spermatogen ic cell types were used to characterize the cellular localization of t hese different transcripts during development of the mouse testis. Bot h forms of proenkephalin mRNA were observed in isolated germ cells by RNA gel-blot analysis, but in distinct developmental patterns; the 1.7 -kb transcripts were present in cells undergoing meiosis and spermioge nesis, whereas the 1.45-kb mRNA was detected primarily in type B sperm atogonia. In contrast, in situ hybridization analysis did not detect s ignificant amounts of the 1.45-kb transcript in any spermatogenic cell type. Using transcript-specific probes, distinct patterns of developm ental expression were evident for the two mRNAs. The 1.45-kb transcrip t was the only form detected in the prepubertal testis, where it was l ocalized mainly in interstitial cells. In contrast, the 1.7-kb transcr ipts were the major mRNAs observed in the adult testis and were locali zed to spermatogenic cells. A transition from the prepubertal to the a dult pattern occurred on or about postnatal day 21, when proenkephalin -expressing pachytene spermatocytes begin to populate the seminiferous tubules. In situ, hybridization analysis further demonstrated that pr oenkephalin gene expression in mutant (at/at) mice, which lack germ ce lls, was identical to that observed in the early prepubertal testis. T hese results suggest that the 1.45-kb proenkephalin mRNA is developmen tally down-regulated in mouse interstitial cells and that this process requires ongoing spermatogenesis.