Laboratory of Drosophila Germ Cell Differentiation

The research group has made significant progress in the developmental genetics of the Drosophila germ line. Dozens of genes involved in germ cell development have been identified in transposon-induced mutagenesis experiments and in RNA interference-based screening using a wide range of Drosophila genetic research tools. By functional analysis of the identified genes, they contributed to the discovery of the subcellular localization of germ line factors and the role of dynamic cytoskeletal rearrangements required in the development of gametes. In their work, they discovered the translation-independent function of mRNA encoded by one of the key genes of embryonic germ cell development and described a microRNA that regulates female fertility. Effective tools have been developed to study the biology of the Drosophila germ cell line. DNA chip technology was used to identify RNA molecules localized in germ plasm. An automated genetic selection method, a gene trapping mutagenizing transposon system, a method for targeted in vivo degradation of proteins, and an RNAi-based screening system combined with video microscopy have been introduced.

The current research goal of the group is to better understand the differentiation and transposon defence of Drosophila adult female germ line stem cells.

Animals generally form a large number of gametes to increase their reproduction success. In most species, the mature gametes are formed by the differentiation of transit amplifying cells derived from continuously functioning germ line stem cells. Stem cells that function in the Drosophila ovary are among the best studied and thus the best known stem cells and serve as a general model of the stemness. The vast majority of our knowledge about the role of somatic environment of stem cells the so-called niche and the mechanism of mutual regulation between the niche and stem cells comes directly from Drosophila research. In Drosophila, structure of niche, communication between its different cell types, and the niche-derived factors that prevent stem cells from differentiation are known. Among the germ cell regulatory factors identified in RNA interference experiments, the research group discovered a novel differentiation factor for ovarian germ cell stem cells. The new factor functions cell autonomously and promotes differentiation of the transit amplifying cells derived from stem cells. Based on structural properties, the new regulatory factor most probably serves as a classical transcription factor. The aim of the current research is to reveal the exact biological and molecular function of the newly identified differentiation factor.

The main function of germ cells is to transmit the undamaged genetic material across generations. A large proportion of eukaryotic genomes consist of mobile genetic elements, called transposons. In order to control the movement of transposons, a specific silencing system has been evolved acting in the animal germ cells. The essence of the silencing system is that the so called piRNAs are generated from the chromosomal sites that consist of arrays of inactive transposons. Mature piRNAs then bind to Piwi proteins and recognise the RNAs transcribing from the active transposons. Piwi proteins organize the so called recognition complex that finally recruits an effector complex involved in heterochromatinization. The resulted local heterochromatin prevents transposons from the further transcription. The elements of the silencing system were originally identified in Drosophila melanogaster then piRNA/Piwi silencing complexes have been found in all higher multicellular animals. However, the molecular link between the target recognising and the effector complexes has not been identified yet. In a previous work, the research group identified the Drosophila Small ovary protein of which depletion caused uncontrolled transposon movement in the germ cells as well as in the niche cells. The Small ovary protein has numerous structural elements that can make it capable to fulfil a central role in the piRNA-mediated silencing. The recent goal of the research group is to prove the working hypothesis that is the Small ovary protein physically interacts both with the piRNA/Piwi recognizing and the effector heterochromatinisation complexes and serves as the yet missing link between them.