Distribution of type A spermatogonia in the mouse is not random

The distribution of type A spermatogonia was studied using drawings of cros s-sectioned tubules at various stages of the spermatogenic cycle of perfusi on-fixed, epoxy-embedded mouse testis. Spermatogonia were classified as eit her positioned opposite the interstitium or opposite the region where two t ubules make contact or in a defined, intermediate region at which the two t ubules diverged. At stage V, the population of type A spermatogonia, compri sed of A(s) through A(al) cells, is randomly positioned around the peripher y of the seminiferous tubule. The A(s) through A(al) population becomes non randomly distributed beginning at stage VI, being located primarily in regi ons where the tubule opposes the interstitium, and remains nonrandom throug h stage III of the next cycle. The A(1) spermatogonia of stage VII, derived from most A(pr) and A(al) spermatogonia, and the A(2) spermatogonia of sta ge IX, derived from the A(1) spermatogonia, are also nonrandomly positioned opposing the interstitium. However, the A(3) population of stage XI become s randomly distributed around the tubule. To our knowledge, these are the f irst data to show that the more primitive spermatogonial types (A(s) to A(a l)) move to specific sites within the seminiferous tubule. Division of the regularly spaced, more primitive spermatogonia (A(s) to A(al)) leads to the spread of their progeny (A(1) to A(4)) laterally along the base of the sem iniferous tubule. The lateral spread from more or less evenly spaced foci e nsures that spermatogenesis is conducted uniformly around the entire tubule . The data also suggest that the position of a seminiferous tubule in the m ouse is stabilized in relationship to other seminiferous tubules.