Chromatin remodelling initiation during human spermiogenesis
Changes in number of nuclear pores in different states of physiologica activity have been reported, but little is known about changing patterns of distribution in the course of cell differentiation. Pore distribution in male germ cells was studied in freeze fracture preparations of immature and mature rodent testis. As in other somatic cells, pores were uniformly and apparently randomly distributed in Sertoli cell nuclei. The nucleus of gonocytes and spermatogonia showed varying degrees of pore clustering. Spermatocytes invariably exhibited very striking pore aggregation with close hexagonal packing in pore-rich areas, and large pore-free areas. In early spermatids, pores appeared to be randomly distributed. As the acrosome formed and spread over the apical pole of the nucleus, pores disappeared ahead of its advancing margin and became more concentrated in the post-acrosomal region. The relationship of pore complexes to the chromosomes and the role of the fibrous lamina are discussed. The question as to whether the changing patterns observed involve movement of pores within fluid nuclear membranes, or a dissolution and reformation of new pores remains unanswered.