DEVELOPMENTAL-CHANGES IN SEMINIFEROUS TUBULE EXTRACELLULAR-MATRIX COMPONENTS OF THE MOUSE TESTIS - ALPHA-3(IV) COLLAGEN CHAIN EXPRESSED AT THE INITIATION OF SPERMATOGENESIS

The temporal expression of type IV collagen, laminin, and entactin in the basal laminae of the seminiferous tubule during development of the mouse testis was determined, Northern blot analysis was used to examine changes in testicular mRNA for alpha 1-alpha 5 type IV collagen (IV) chains in mice ranging in age from newborn to adult (60 days). Levels for mRNA alpha 1(IV) and alpha 2(IV) chains were highest in newborns through Day 5 and remained elevated through Day 10, but then sharply declined to adult values by Day 30. In sharp contrast, alpha 3(IV) and alpha 4(IV) chain levels were low in newborns, peaked at Day 10, and then declined to adult values by Day 30. 5(IV) mRNA was elevated in newborns and at Days 5 and 10 before dropping to adult levels by Day 30. Changes in the deposition of alpha 1, alpha 2, and alpha 3(IV) collagen chains, laminin, and entactin into the inner and outer basal laminae of the seminiferous tubule were determined from the beginning of tubule formation (embryonic Day 12.5) through adulthood by immunofluorescence microscopy using polyclonal antibodies for these constituents, The alpha 1 and alpha 2(IV) chains, laminin, and entactin were deposited into the inner basal lamina at embryonic Day 12.5 and into the newly formed outer basal lamina at Day 5 after birth. The alpha 3(IV) chains were deposited into both the inner and outer basal laminae at Day 5. Thus, testicular alpha 1-alpha 3(IV) mRNA levels coincide with the incorporation of detectable collagen chains into the seminiferous basal laminae, suggesting transcriptional control of these alpha(IV) chains. Expression of the alpha 3(IV) chain coincides with the initiation of spermatogenesis, suggesting a functional role of this chain in spermatogonial proliferation.