TARGETING OF ENDOGENOUS SULFATED GLYCOPROTEIN-1 AND GLYCOPROTEIN-2 TOLYSOSOMES WITHIN NONCILIATED CELLS OF THE EFFERENT DUCTS DURING POSTNATAL-DEVELOPMENT OF THE RAT

Sulfated glycoprotein (SGP)-1 and -2, secretory products of Sertoli ce lls, are secreted into the lumen of seminiferous tubules where they bi nd to late spermatids. Once released, the spermatozoa traverse the eff erent ducts where these proteins detach from their surface and are end ocytosed by the nonciliated cells. In adult animals, SGP-1 and SGP-2 a re also synthesized by nonciliated cells and targeted from the Golgi a pparatus to lysosomes. The purpose of the present study was to determi ne the pattern of expression of SGP-1 and SGP-2 within nonciliated cel ls during postnatal development. The efferent ducts of animals at diff erent postnatal ages were prepared for an electron microscopic immunoc ytochemical quantitative analysis as well as for Northern blot analysi s. The data expressed as labeling content (no. gold particles/mu m(2) and taking into account the volume of the endocytic organelles and the cell) revealed that anti-SGP-1 labeling in endosomes of nonciliated c ells was minimal at 15, 21, and 29 days of age. On the other hand, the lysosomal labeling content showed a significant increase by day 29 co mpared to 15 and 21-day-old animals indicating that an endogenous form of SGP-1 was being synthesized by nonciliated cells and targeted to l ysosomes. By day 39 a significant increase in endosomal labeling occur red; this was attributed to the endocytosis of Sertoli-derived SGP-1 w hich coincided with the entry of spermatozoa into the lumen of these d ucts at this age. Lysosomal labeling showed further significant increa ses at days 39, 49, and then again at day 90. Northern blot analysis d etected SGP-1 mRNA transcripts at all postnatal ages examined. White d ecreases or increases in transcripts could not be determined due to th e greater amount of tissue present with increasing age, these data tak en together support the idea of an endogenous form of SGP-1 being synt hesized by nonciliated cells and targeted to lysosomes during postnata l development. In the case of SGP-2, endosomal labeling was minimal at 15, 21, and 29 days of age but was significantly increased by day 39, with similar values at all subsequent ages. The high value at day 39 was attributed to the endocytosis of SGP-2 which coincided with the en try of spermatozoa into the lumen at this age. Lysosomal labeling, on the other hand, was low at days 15 and 21 but peaked at day 29 at a ti me when endosomal labeling was minimal. These results suggested the sy nthesis of an endogenous form of SGP-2 which was being targeted to lys osomes. Similar values for SGP-2 lysosomal labeling comparable to that at day 29 were obtained at all other ages. Since SGP-2 endosomal labe ling was significantly increased at day 39 and maintained thereafter, it is suggested that labeling in lysosomes at this and subsequent ages could also be due to the endocytosis of Sertoli-derived SGP-2. Howeve r, Northern blot analysis confirmed the presence of mRNA transcripts f or SGP-2 at all postnatal ages examined, although increases or decreas es in their amount were not determined. These results thus consolidate the hypothesis of an endogenous form of SGP-2 being synthesized by no nciliated cells and targeted to lysosomes. Finally, since the amounts of endogenous SGP-1 and SGP-2 peak at different ages, it is suggested that different factors are involved in regulation of these two protein s during postnatal development. (C) 1995 Wiley-Liss, Inc.