INVESTIGATION OF THE POTENTIAL ROLE OF THE GERM-CELL COMPLEMENT IN CONTROL OF THE EXPRESSION OF TRANSFERRIN MESSENGER-RNA IN THE PREPUBERTAL AND ADULT-RAT TESTIS

Iron is required for the normal development of germ cells during sperm atogenesis. Because these cells have no direct access to systemic iron , there exists a shuttle system involving production and secretion of the iron-transporting protein transferrin by the Sertoli cells. Previo us reports using cultures of immature Sertoli cells exposed to adult g erm cells, or in vivo studies involving germ cell-depleted adult rat t estes, concluded that production of transferrin by Sertoli cells is mo dulated by germ cell complement. In the present study we have used in situ hybridisation with cRNA probes directed against the 5' and 3' end s of transferrin mRNA to examine the pattern of expression of transfer rin in the immature and adult rat testis. Adult rats were treated with ethane dimethane sulphonate of methoxyacetic acid (MAA) to manipulate their testosterone levels or germ cell complement respectively. Initi al findings obtained using the 3' probe showed a decrease in transferr in mRNA associated with round spermatid depletion. However, these data were not confirmed by in situ hybridisation when the 5' probe was use d. The specificity of the probes was examined using Northern blotting and the 3' probe was found to hybridise to the germ cell transcript fo r hemiferrin even under conditions of high stringency. Examination of immature and pubertal rat testes by in situ hybridisation using the 5' transferrin-specific probe found that as early as 14 days of age the level of expression of transferrin mRNA was clearly different between tubules, and the mRNA appeared to be expressed in Leydig cells on and after day 31. In the adult rat testis, maximal expression of transferr in mRNA was found at stages VIII-XIV, calling into question the interp retation of the results of some previous studies showing expression of transferrin mRN4 at all stages of the spermatogenic cycle. This stage -specific pattern of expression was not altered by acute cell depletio n using MAA. However, Northern blot analysis showed a statistically si gnificant increase in transferrin mRNA expression at 7 days after MAA treatment when pachytene spermatocytes were depleted from tubules at a ll stages of the spermatogenic cycle at which transferrin is normally expressed. In conclusion, we found that transferrin mRNA expression wa s not modulated by round spermatids as has been reported previously bu t that meiotic germ Cells may influence expression of transferrin at s pecific stages of the spermatogenic cycle.