To assess the proliferation of wild type and mutant FCs, we compared the sizes of corresponding mutant and wild type twin clones (Fig.?5ACD). activating the secretion of the BMP ligand (GBB) in male somatic stem cells, which in turn activates the BMP pathway in GSCs (Kawase et al., 2004). The progenitors of GSCs, which are called primordial germ cells (PGCs), also utilise BMP signalling through DPP to repress BAM in the larval ovary (Gilboa and Lehmann, 2004). Maintenance of FSCs in the ovary not only requires DPP signalling but also and pathway activity (for a review, see Kirilly and Xie, 2007). Thus, BMP signalling contributes both directly and indirectly to stem cell maintenance in various stem cell populations, but it functions in conjunction with other different external signals to suppress stem cell differentiation. However, common stem cell autonomous components that maintain stem cell properties and prevent differentiation have remained unknown. Here we report that this protein kinase encoded by the gene (protein (BALL) is usually orthologous to the Vaccinia-related Kinases (VRKs) of vertebrates and most closely related to VRK-1 (Aihara et al., 2004). VRKs are found in all metazoan species ranging from worms to humans. VRKs of different species were found to phosphorylate the Barrier-to-Autointegration Factor (BAF) (Bengtsson and Wilson, 2006; Gorjncz et al., 2007; Lancaster et al., 2007; Nichols et al., 2006), which is usually involved in the assembly of the nuclear lamina in (Gorjncz GSK690693 et al., 2007) and the organisation GSK690693 of chromatin in the nucleus (Margalit et al., 2007). Moreover, hypomorphic mutations in cause aberrant chromatin organisation in the oocyte nucleus and an altered pattern of histone modifications (Ivanovska et al., 2005). The analysis of null mutants revealed defects in proliferating tissues of the larvae, including the GSK690693 brain and imaginal discs (Cullen et al., 2005). We have used GSK690693 systemic null mutants and mosaic analyses to characterise the function of BALL in both progenitor cells and niche-dependent stem cells. We found that BALL is required to maintain self-renewal of stem cells, which suggests that this previously explained defects Mouse monoclonal to MYST1 in proliferating tissues GSK690693 of mutant animals is caused by the premature or unscheduled differentiation of progenitor cells rather than a general function of BALL for cellular proliferation. RESULTS BALL is essential to maintain the larval germline In order to assess the function of in proliferating tissue and in stem cells, we generated a null allele of (homozygotes (hereafter referred to as mutants) pass away during the pupal stage, confirming previous results explained for other null alleles (Cullen et al., 2005). mutants already show severe morphological defects by the end of larval development which include considerably reduced gonads in both sexes, the absence of imaginal discs and severely diminished larval brains. This mutant phenotype is usually solely due to the mutation, as a genomic transgene rescued the mutants to produce viable and fertile adults (supplementary material Fig. S1). We explored the function of BALL in developing male and female gonads. Growth of larval testes relies on asymmetric, niche-supported divisions of GSCs, whereas growth of larval ovaries relies on symmetric divisions of primordial germ cells (PGCs) (Dansereau and Lasko, 2008). Both larval cell types are derived from embryonic PGCs, which reside in the primitive gonads of embryos. In order to establish whether the initial quantity of PGCs was affected in mutant embryos, we counted their number in embryonic gonads. mutants contained on average 10.2 PGCs (SD?=?1.8, mutants is not caused by a reduced quantity of embryonic PGCs. We next asked when the size reduction of the male gonads occurs during larval development. In early larval testes, about 8C12 PGCs adopt GSC fate after their recruitment to the somatic hub cells (Fig.?1A). GSCs then divide and give rise to self-renewed GSCs and gonialblasts, respectively. The gonialblasts undergo four incomplete cell divisions and form a 16-cell germline cyst. GSCs and differentiating cysts can be distinguished by their position in the developing testis and by the expression of the adducin-related protein, HTS (Fig.?1A). During mid larval development of wild.