The function of the lampbrush loops formed by the Y chromosome of Drosophila hydei in spermatocyte nuclei

Molecular evidence for partial inactivation of Y loops in T(X:Y)56 males from D. hydei

Using loop-specific DNA clones, we established that the T(X:Y)56 (Hackstein and Hennig 1982) chromosome, formerly thought to be deleted for the Yshort arm and the associated 'nooses' loops is actually an XYS X YL combination. It carries, adjacent to the translocation junction, the complete and uninterrupted set of the two dysfunctional 'nooses' domains. The morphologically altered and functionally defective loops are transcribed at about 50% of the normal rate. Transcripts in one of the two 'nooses' domains are preferentially underrepresented and their distribution in the spermatocyte nucleus is distorted, presumably as a consequence of a spreading effect. No alteration in transcript size or in the correct strand selection, and no variegation of transcription on the single spermatocyte level, were observed. In another translocation T(X:Y)97, in which 'tubular ribbons' were reported to be inactivated (Hess 1970), complete elimination of DNA sequences is observed. A possible mechanism for the position effect inactivation of Y loops in X:Y translocations is discussed briefly.

"Hybrid" X--Y translocation chromosomes of Drosophila hydei and D. neohydei

The Y chromosome of Drosophila carries fertility genes which, in part, develop lampbrush loops during the meiotic prophase. Hybrid males from crosses between D. hydei and D. neohydei are fertile although the morphology of the lampbrush loops differs between both species. With the aid of X ray induced "hybrid" X-Y translocation chromosomes the question has been studied whether Y chromosomal genes of D. neohydei can substitute deletions in the Y chromosome of D. hydei. Although the induction of translocation chromosomes almost regularly results in an inactivation of the translocated Y fragment within a few generations, one case of successful complementation has been demonstrated. Furthermore, a new lampbrush loop pair has been detected in D. neohydei which is morphologically similar to the "nooses" of D. hydei. Preliminary evidence for the location of the lampbrush loops on the Y chromosome of D. neohydei is discussed.

RNA synthesis in spermatocytes and spermatids and preservation of meiotic RNA during spermiogenesis in the mouse

The rate of RNA synthesis at different stages of spermatogenesis in the mouse, and the preservation of RNA from the diploid to the haploid phase of spermatogenesis were studied in homogeneous germ cell fractions separated by velocity sedimentation at unit gravity. The uridine pool expansion method was used for determining the rate of RNA synthesis: seminiferous tubules were labelled in culture with increasing concentrations of [3H]-uridine and the incorporated radioactivity was estimated in cell fractions separated by velocity sedimentation. The results indicate that before nuclear elongation, round spermatids (steps 1 to 8 of spermiogenesis) synthesize RNA at the same rate per DNA content as middle-late pachytene spermatocytes. The preservation of RNA molecules synthesized in meiosis was investigated by labelling pachytene spermatocytes with T3H]uridine in vivo and collecting samples of germ cells at definite stages of spermatogenesis at various time intervals thereafter. The results show that a considerable proportion the RNA synthesized during the pachytene stage is preserved through spermatid development until late spermiogenesis.