Organ growth during development and tissue regeneration occur through a small population of cells known as stem cells. Manipulation of these cells is emerging as a powerful approach in regenerative medicine for restoring tissue from within. It is therefore essential to understand the mechanisms by which stem cells induce organ growth to perform manipulations in vivo. In this context, scientists on the EU-funded 'Somatic control of primordial germ cell proliferation' (PGC PROLIFERATION) project used the fruit fly Drosophila melanogaster as a model organism. Germ line stem cells (GSCs) in this system exhibit similar biological principles to other stem cells in terms of maintenance and differentiation. In female flies, the ovaries form during embryogenesis. At the larval stages, somatic niches form and maintain adult GSCs in an undifferentiated state. Upon division of GSCs, one of the daughter cells leaves the protective environment of the niche and differentiates into a cystoblast. This process is also regulated through cells called escort cells. To unravel which somatic signalling pathways regulate GSC maintenance and differentiation, researchers performed a thorough screen. The woc gene proved to be essential for proper GSC differentiation. Flies lacking expression of this gene in their escort cells failed to maintain the GSC niche and developed ovarian tumours. Further analysis of the Woc protein, showed that it acted as a transcription factor enabling cystoblast differentiation through signal transducer and activator of transcription (Stat) signalling. This result demonstrated the so far unknown role of Stat signalling in GSC differentiation. To explain the dual regulatory role of Stat signalling, scientists proposed a theory whereby Stat maintains the adhesion of GSC with the appropriate somatic cell type. Depending on the cell type, this contact elicits a different response within the germ cells. Taken together, the data of the PGC PROLIFERATION study underscore the importance of adhesion between niche cells and stem cells, but also between differentiating stem cell daughters and their support cells.
Stem cell, Drosophila melanogaster, tissue regeneration, germ line stem cell, cystoblast, escort cell, woc gene, ovarian tumour, Stat signalling