Studies on sex-organ development. Changes in nuclear and chromatin composition and genomic activity during...

We developed a technique to separate nuclei of rooster testis by centrifugation through a discontinuous sucrose density gradient and by sedimentation at unit gravity. Four different major fractions obtained from testicular nuclei and one from the vas deferens were characterized according to their velocity of sedimentation, morphology and DNA content. The ratios (w/w) of basic proteins, non-histone proteins and RNA to DNA decreased during spermiogenesis both in nuclei and chromatin. Changes in the electrophoretic patterns of histones and non-histone proteins were detected especially in the elongated spermatids. The lack of uptake of [3H]uridine in elongating and elongated spermatids and in spermatozoa was demonstrated by radioautography and by the detection of labelled RNA extracted from different fractions of nuclei. Template activity for RNA synthesis and the binding of actinomycin D by testicular nuclei reached a peak in the elongated spermatid stage, when the histones are replaced by the protamine.