Analysis of nuclear proteins in primary spermatocytes of Drosophila hydei: The correlation of nuclear proteins with the function of the Y chromosomal loops

A group of non-Y encoded Drosophila hydei primary spermatocyte nuclear glycoproteins exhibits epitopes depending on formation of Y chromosomal giant lampbrush loops

In wild-type Drosophila hydei (genotype X/Y) four different primary spermatocyte nuclear glycoproteins, classified as non-Y encoded because of their occurrence in X/O genotypes, were demonstrated to possess a few epitopes that depended on formation of the Y chromosomal giant lampbrush loops threads (th; Mr 55,000 proteins) or pseudonucleolus (ps; Mr 38,000, 58,000 and 98,000 proteins). The epitopes reacted with lectins and/or antibodies in vitro lectin-/immunoreplica of primary spermatocyte total nuclear protein), and were lacking in mutants not possessing the respective loops. Those dependent on ps reacted with human sera. Epitopes restricted to proteins from th-forming spermatocytes reacted with lectin Con A (specific for D-Man and/or D-Glc) and antibodies directed against mouse immunoglobulins (AIA). In situ experiments (immunofluorescence microscopy of primary spermatocyte nuclei) revealed antibody cross-reactions with the respective loops. The reagents stained the distal (fused) sections and proximal (compact) parts of ps (human sera) or the proximal (compact) parts of th (AIA). Reaction with the latter loops was significantly repressed after absorption of AIA with the L-Fuc carbohydrate unit, classifying the AIA as fucosyl specific, and the epitopes along th as L-Fuc carbohydrate units.

Structure and function of Y chromosomal DNA. II. Analysis of lampbrush loop associated transcripts in nuclei of primary spermatocytes of Drosophila hydei by in situ hybridization using asymmetric RNA probes of four different families of repetitive DNA

pSP64/65 subclones of four different families of repetitive sequences on the Y chromosome of Drosophila hydei were used for in vitro synthesis of labelled RNA. Pairs of RNA probes of opposite strand polarity were employed to analyse RNAs transcribed on, or associated with, various Y chromosomal lampbrush loops in nuclei of primary spermatocytes of D. hydei. The results of RNA filter analysis and in situ hybridization experiments can be generalized as follows: (1) Y-specific transcripts are heterogeneous in length and are synthesized on lampbrush loops. (2) Transcription of tandemly repeated sequences is usually strand specific. (3) Members of the same sequence family can be found in transcripts from different lampbrush loops. (4) Transcripts not coded by the Y chromosome are accumulated on different subregions of Y chromosomal lampbrush loops.

Lampbrush loop-specific protein of Drosophila hydei

By immunofluorescence techniques and protein blotting experiments we have shown that an antiserum specifically reacts with a Mr 80,000 protein (the "Ps protein") in the lampbrush loop " pseudonucleolus " in spermatocyte nuclei of Drosophila hydei. Comparative studies of X/Y and X/0 testes indicate that the gene encoding the Ps protein is not located on the Y chromosome but on an autosome or the X chromosome. The Ps protein is tissue specific. It is likely to be a rather conserved protein since the antigenic determinant recognized by the antiserum could be detected in the spermatocyte nuclei of a number of other Drosophila species. For those species with prominent Y chromosomal lampbrush loops, it could be shown that the cross-reaction is, as in D. hydei, associated with a specific Y chromosomal loop.

The Croonian Lecture, 1981. Lampbrush chromosomes

Lampbrush chromosomes were first observed nearly 100 years ago, and this lecture attempts a historical survey of what has been learnt from their study, particularly that over the past 30 years. There have been many controversies concerning the structure and functional significance of lampbrush chromosomes, and although their general structural layout has now, after several misconceptions, been firmly established their functional significance remains controversial. Research on lampbrush chromosomes played a significant part in establishing that chromatids in the germ lines of eukaryotic organisms are unineme in regard to DNA, and thereby exposed the C-value paradox. It also helped to establish that a DNA duplex is continuous throughout the length of a chromatid, but that the DNA/histone complex is at intervals reflected back on itself to form lateral loops. This organization, at one time thought to be a special feature of lampbrush chromosomes, now appears to be widespread in chromosomes undergoing compaction. However, despite attempts to determine the sequence organization of those portions of the DNA that are transcribed by lampbrush chromosomes, the function of these transcripts remains an open question, and the C-value paradox is still unresolved.