Advantages of a P-element construct containing MtnA sequences for the identification of patterning and cell determination genes in Drosophila melanogaster

Genetic basis for developmental homeostasis of germline stem cell niche number: a network of Tramtrack-Group nuclear BTB factors

The potential to produce new cells during adult life depends on the number of stem cell niches and the capacity of stem cells to divide, and is therefore under the control of programs ensuring developmental homeostasis. However, it remains generally unknown how the number of stem cell niches is controlled. In the insect ovary, each germline stem cell (GSC) niche is embedded in a functional unit called an ovariole. The number of ovarioles, and thus the number of GSC niches, varies widely among species. In Drosophila, morphogenesis of ovarioles starts in larvae with the formation of terminal filaments (TFs), each made of 8–10 cells that pile up and sort in stacks. TFs constitute organizers of individual germline stem cell niches during larval and early pupal development. In the Drosophila melanogaster subgroup, the number of ovarioles varies interspecifically from 8 to 20. Here we show that pipsqueak, Trithorax-like, batman and the bric-à-brac (bab) locus, all encoding nuclear BTB/POZ factors of the Tramtrack Group, are involved in limiting the number of ovarioles in D. melanogaster. At least two different processes are differentially perturbed by reducing the function of these genes. We found that when the bab dose is reduced, sorting of TF cells into TFs was affected such that each TF contains fewer cells and more TFs are formed. In contrast, psq mutants exhibited a greater number of TF cells per ovary, with a normal number of cells per TF, thereby leading to formation of more TFs per ovary than in the wild type. Our results indicate that two parallel genetic pathways under the control of a network of nuclear BTB factors are combined in order to negatively control the number of germline stem cell niches.

The NemaGENETAG initiative: large scale transposon insertion gene-tagging in Caenorhabditis elegans

The nematode Caenorhabditis elegans is a widely appreciated, powerful platform in which to study important biological mechanisms related to human health. More than 65% of human disease genes have homologues in the C. elegans genome, and essential aspects of mammalian cell biology, neurobiology and development are faithfully recapitulated in this organism. The EU-funded NemaGENETAG project was initiated with the aim to develop cutting-edge tools and resources that will facilitate modelling of human pathologies in C. elegans, and advance our understanding of animal development and physiology. The main objective of the project involves the generation and evaluation of a large collection of transposon-tagged mutants. In the process of achieving this objective the NemaGENETAG consortium also endeavours to optimize and automate existing transposon-mediated mutagenesis methodologies based on the Mos1 transposable element, in addition to developing alternatives using other transposon systems. The final product of this initiative-a comprehensive collection of transposon-tagged alleles-together with the acquisition of efficient transposon-based tools for mutagenesis and transgenesis in C. elegans, should yield a wealth of information on gene function, immediately relevant to key biological processes and to pharmaceutical research and development.

TGFbeta superfamily members in spermatogenesis: setting the stage for fertility in mouse and Drosophila

Male germ cell development involves a tightly controlled sequence of differentiation switches, from the time that this lineage is specified in the embryo to the moment of sperm release for transport from the testis. Recent research findings and technological advances have allowed key mediators of developmental switches to be identified, and several members of the TGFbeta superfamily of ligands have been implicated at distinct points of male gamete formation and spermatogenesis. This paper reviews the multiple points of control mediated by TGFbeta superfamily signalling molecules during differentiation of the mammalian male germ cell. Comparisons have been made with the Drosophila testis for which genetic analysis has yielded new information concerning the roles of TGFbeta signalling in early germ cell differentiation.

Cross-regulation among the polycomb group genes in Drosophila melanogaster

Genes of the Polycomb group in Drosophila melanogaster function as long-term transcriptional repressors. A few members of the group encode proteins found in two evolutionarily conserved chromatin complexes, Polycomb repressive complex 1 (PRC1) and the ESC-E(Z) complex. The majority of the group, lacking clear biochemical functions, might be indirect regulators. The transcript levels of seven Polycomb group genes were assayed in embryos mutant for various other genes in the family. Three Polycomb group genes were identified as upstream positive regulators of the core components of PRC1. There is also negative feedback regulation of some PRC1 core components by other PRC1 genes. Finally, there is positive regulation of PRC1 components by the ESC-E(Z) complex. These multiple pathways of cross-regulation help to explain the large size of the Polycomb group family of genes, but they complicate the genetic analysis of any single member.

Localized Notch signal acts through eyg and upd to promote global growth in Drosophila eye

Notch (N) signal is activated at the dorsoventral (DV) border of the Drosophila eye disc and is important for growth of the eye disc. In this study, we showed that the Pax protein Eyg is a major effector mediating the growth promotion function of N. eyg transcription is induced by N signaling occurring at the DV border. Like N, eyg controls growth of the eye disc. Loss of N signaling can be compensated by overexpressing eyg, whereas loss of the downstream eyg blocked the function of N signaling. In addition, we showed that N and eyg could induce expression of upd, which encodes the ligand for the Jak/STAT pathway and acts over long distance to promote cell proliferation. Loss of eyg or N can be compensated by overexpressing upd. These results suggest that upd is a major effector mediating the function of eyg and N. The functional link from N to eyg to upd explains how the localized Notch activation can achieve global growth control.

Trl-GAGA directly interacts with lola like and both are part of the repressive complex of Polycomb group of genes

Epigenetic inheritance to maintain the expression state of the genome is essential during development. In Drosophila, the cis regulatory elements, called the Polycomb Response Elements (PREs) function to mark the epigenetic cellular memory of the corresponding genomic region with the help of PcG and trxG proteins. While the PcG genes code for the repressor proteins, the trxG genes encode activator proteins. The observations that some proteins may function both as PcG and trxG member and that both these group of proteins act upon common cis elements indicate at least a partial functional overlap among these proteins. Trl-GAGA was initially identified as a trxG member but later was shown to be essential for PcG function on several PREs. In order to understand how Trl-GAGA functions in PcG context, we have looked for the interactors of this protein. We identified lola like, aka batman, as a strong interactor of GAGA factor in a yeast two-hybrid screen. lolal also interacts with polyhomeotic and, like Trl, both lolal and ph are needed for iab-7PRE mediated pairing dependent silencing of mini-white transgene. These observations suggest a possible mechanism of how Trl-GAGA plays a role in maintaining the repressed state of target genes involving lolal, which may function as a mediator to recruit PcG complexes.

batman Interacts with polycomb and trithorax group genes and encodes a BTB/POZ protein that is included in a complex containing GAGA factor

Polycomb and trithorax group genes maintain the appropriate repressed or activated state of homeotic gene expression throughout Drosophila melanogaster development. We have previously identified the batman gene as a Polycomb group candidate since its function is necessary for the repression of Sex combs reduced. However, our present genetic analysis indicates functions of batman in both activation and repression of homeotic genes. The 127-amino-acid Batman protein is almost reduced to a BTB/POZ domain, an evolutionary conserved protein-protein interaction domain found in a large protein family. We show that this domain is involved in the interaction between Batman and the DNA binding GAGA factor encoded by the Trithorax-like gene. The GAGA factor and Batman codistribute on polytene chromosomes, coimmunoprecipitate from nuclear embryonic and larval extracts, and interact in the yeast two-hybrid assay. Batman, together with the GAGA factor, binds to MHS-70, a 70-bp fragment of the bithoraxoid Polycomb response element. This binding, like that of the GAGA factor, requires the presence of d(GA)n sequences. Together, our results suggest that batman belongs to a subset of the Polycomb/trithorax group of genes that includes Trithorax-like, whose products are involved in both activation and repression of homeotic genes.