DIFFERENTIAL DISTRIBUTION OF TYPE-IV COLLAGEN CHAINS IN THE DEVELOPING RAT TESTIS AND OVARY

The localization of type IV collagen alpha 1-alpha 5 chains in the dif ferentiating rat testis and ovary was studied by immunocytochemistry. The initial formation of the testis and ovary included the appearance of collagen alpha 1/alpha 2(IV) chains in the gonadal blastemas. Upon further differentiation of the epithelia of the gonads alpha 1/alpha 2 (IV) chains became localized in all of the respective basement membran es (BMs). The alpha 3, alpha 4 and alpha 5 chains of type IV collagen were not detectable in the prenatal rat testis and ovary. With the pos tnatal differentiation of the rat testis the alpha 3-alpha 5(IV) chain s gradually appeared, and were localized in BMs of the testicular cord s and seminiferous tubules, rete cords, myoid cells, surface epitheliu m, Leydig cells, and in some blood vessels. In the postnatal rat ovary , the a3(IV) chain appeared in the BMs of small cortical follicles whe reas the BMs of secondary and more deeply localized follicles were dev oid of this chain. The alpha 1/alpha 2(IV) chains were abundant in the theca. A reaction for a3-a5(IV) chains also appeared in the BM of the ovarian surface epithelium and of some blood vessels after birth. The present results show that the alpha 3-alpha 5(IV) chains are not only less widely distributed than the alpha 1/alpha 2(IV) chains but are a lso synthesized much later in development. The late appearance of the a3-a5(IV) chains shows that the development of the mature testicular a nd ovarian BMs is a long process and that the time schedule for the sy nthesis of these chains is different from that of many other extracell ular matrix proteins. A careful analysis of the expression of alpha 3( IV) chain may be useful in the further study of the kinetics and regul ation of ovarian follicular growth.