Transcription of repetitive DNA sequences in the lampbrush loop pair Nooses formed by sterile alleles of fertility gene Q on the Y chromosome of Drosophila hydei

Drosophila as a Model System for Studying of the Evolution and Functional Specialization of the Y Chromosome

The Y chromosome is one of the sex chromosomes found in males of animals of different taxa, including insects and mammals. Among all chromosomes, the Y chromosome is characterized by a unique chromatin landscape undergoing dynamic evolutionary change. Being entirely heterochromatic, the Y chromosome as a rule preserves few functional genes, but is enriched in tandem repeats and transposons. Due to difficulties in the assembly of the highly repetitive Y chromosome sequence, deep analyses of Y chromosome evolution, structure, and functions are limited to a few species, one of them being Drosophila melanogaster. Despite Y chromosomes exhibiting high structural divergence between even closely related species, Y-linked genes have evolved convergently and are mainly associated with spermatogenesis-related activities. This indicates that male-specific selection is a dominant force shaping evolution of Y chromosomes across species. This review presents our analysis of current knowledge concerning Y chromosome functions, focusing on recent findings in Drosophila. Here we dissect the experimental and bioinformatics data about the Y chromosome accumulated to date in Drosophila species, providing comparative analysis with mammals, and discussing the relevance of our analysis to a wide range of eukaryotic organisms, including humans.

Satellite DNA-containing gigantic introns in a unique gene expression program during Drosophila spermatogenesis

Intron gigantism, where genes contain megabase-sized introns, is observed across species, yet little is known about its purpose or regulation. Here we identify a unique gene expression program utilized for the proper expression of genes with intron gigantism. We find that two Drosophila genes with intron gigantism, kl-3 and kl-5, are transcribed in a spatiotemporal manner over the course of spermatocyte differentiation, which spans ~90 hours. The introns of these genes contain megabases of simple satellite DNA repeats that comprise over 99% of the gene loci, and these satellite-DNA containing introns are transcribed. We identify two RNA-binding proteins that specifically localize to kl-3 and kl-5 transcripts and are needed for the successful transcription or processing of these genes. We propose that genes with intron gigantism require a unique gene expression program, which may serve as a platform to regulate gene expression during cellular differentiation.

Introns are non-coding elements of eukaryotic genes, often containing important regulatory sequences. Curiously, some genes contain introns so large that more than 99% of the gene locus is non-coding. One of the best-studied large genes, Dystrophin, a causative gene for Duchenne Muscular Dystrophy, spans 2.2Mb, only 11kb of which is coding. This phenomenon, ‘intron gigantism’, is observed across species, yet little is known about its purpose or regulation. Here we identify a unique gene expression program utilized for the proper expression of genes with intron gigantism using Drosophila spermatogenic genes as a model system. We show that the gigantic introns of these genes are transcribed in line with the exons, likely as a single transcript. We identify two RNA-binding proteins that specifically localize to the site of transcription and are needed for the successful transcription or processing of these genes. We propose that genes with intron gigantism require a unique gene expression program, which may serve as a platform to regulate gene expression during cellular differentiation.

Mammalian DNMTs in the male germ line DNA of Drosophila

It is controversial whether DNA methylation plays a functional role in Drosophila. We have studied testis DNA of Drosophila melanogaster Meigen, 1830 with antisera against 5-methylcytosine (5mC) and found no evidence for the presence of significant amounts of 5mC. Reactions occur only with 1 of 3 5mC antisera, but they are restricted to nuclear regions without detectable amounts of DNA. The antisera apparently cross-react with other nuclear components. If the murine de novo DNA methyltransferases, DNMT3A and DNMT3B, are expressed under the control of the spermatocyte-specific beta2-tubulin promoter in testes, DNA methylation is not increased and no effects on the fertility of the fly are seen. DNA methylation has, therefore, no functional relevance in the male germ line of Drosophila.