Low-affinity nerve growth factor receptor is expressed during testicular morphogenesis and in germ cells at specific stages of spermatogenesis.

Nerve growth factor (NGF) is essential for neuronal development and differentiation. Recent reports have shown that its low-affinity receptor (LNGFR) is expressed and developmentally regulated in a broad range of embryonic and adult tissues outside the nervous system, although the functions of the receptor in such tissues remain unknown. Recently, NGF and LNGFR have been detected in adult mouse, rat, and human testis. The results of the present work demonstrate that LNGFR is expressed much before the onset of spermatogenesis in both mouse and rat testis. In situ hybridization shows that the mRNA for LNGFR is expressed in the peritubular cells of the embryonic mouse testis. Immunohistochemical analysis of the rat testis shows LNGFR-expressing cells to be scattered in the intertubular compartment in the embryonic testis, and to become organized in a cellular layer that surrounds myoid cells of the seminiferous tubules during postnatal development. Furthermore, in peripuberal and adult mouse and rat testis we have identified the expression of an abundant and shorter mRNA of 3.2 kb that cross hybridizes to the low-affinity NGF receptor transcript (3.7 kb). This shorter mRNA species, which appears at the beginning of spermatogenesis in the adult, has been identified by in situ hybridization and by Northern blot with RNA isolated from homogeneous populations of meiotic germ cells to be expressed by pachytene spermatocytes and round spermatids. Our results suggest a complex developmental role for LNGFR during testicular morphogenesis and identify the expression, at specific stages of spermatogenesis, of a new germ cell-specific transcript homologous to the receptor RNA.