A key feature of many adult stem cell lineages is that stem cell daughters destined for differentiation undergo several transit amplifying (TA) divisions before initiating terminal differentiation, allowing few and infrequently dividing stem cells to produce many differentiated progeny. Although the number of progenitor divisions profoundly affects tissue (re)generation, and failure to control these divisions may contribute to cancer, the mechanisms that limit TA proliferation are not well understood. Here, we use a model stem cell lineage, the Drosophila male germ line, to investigate the mechanism that counts the number of TA divisions. bam ͉ spermatogenesis ͉ Drosophila ͉ transit amplifying cell division A dult stem cells act throughout life to replenish differentiated cells lost to normal turnover or injury. In many adult stem cell lineages, stem cell daughters undergo transit amplifying (TA) mitotic division before terminal differentiation. The number of TA divisions strongly influences the capacity of adult stem cells to regenerate and repair tissues (1). In addition, strict limits on TA cell proliferation may help prevent accumulation of oncogenic replication errors. Defects in the mechanisms that count and limit the number of TA divisions may therefore predispose to cancer. Indeed, recent evidence points toward cancer initiating events occurring in TA cells in leukemia (2, 3).Despite the importance for normal tissue homeostasis and cancer, the mechanisms that specify the number of TA divisions are not understood. Here, we use the Drosophila male germ line model adult stem cell lineage to investigate the mechanisms that normally set developmentally programmed limits on proliferation of TA cells. Drosophila melanogaster male germ line stem cells (GSCs) lie in a niche at the tip of the testis, attached to somatic hub cells, and are maintained by signals from the hub and f lanking somatic stem cells (4 -7). When a GSC divides, one daughter remains in the niche and self-renews, while the other is displaced away and initiates differentiation. The resulting differentiating gonialblast, which is enveloped by a pair of somatic cells, founds a clone of 16 spermatogonia through four synchronous TA divisions with incomplete cytokinesis. Soon after the fourth TA division, the resulting 16 germ cells undergo premeiotic DNA synthesis in synchrony and switch to the spermatocyte program of cell growth, meiosis, and terminal differentiation. As spermatocytes, the cells increase in volume 25-fold, take on a distinctive morphology, and turn on a unique gene expression program for spermatid differentiation (8) (Fig. 1A).The anatomy of developing germ cell cysts makes the Drosophila germ line especially well suited for investigating how the number of TA divisions is controlled. Because TA sister cells descended from a common gonialblast are contained within a common somatic cell envelope and divide in synchrony, the number of rounds of TA division executed prior to differentiation can be assessed by counting the number of dif...

The Drosophila fusome is a germ cell-specific organelle assembled from membrane skeletal proteins and membranous vesicles. Mutational studies that have examined inactivating alleles of fusome proteins indicate that the organelle plays central roles in germ cell differentiation. Although mutations in genes encoding skeletal fusome components prevent proper cyst formation, mutations in the bag-of-marbles gene disrupt the assembly of membranous cisternae within the fusome and block cystoblast differentiation altogether. To understand the relationship between fusome cisternae and cystoblast differentiation, we have begun to identify other proteins in this network of fusome tubules. In this article we present evidence that the fly homologue of the transitional endoplasmic reticulum ATPase (TER94) is one such protein. The presence of TER94 suggests that the fusome cisternae grow by vesicle fusion and are a germ cell modification of endoplasmic reticulum. We also show that fusome association of TER94 is Bam-dependent, suggesting that cystoblast differentiation may be linked to fusome reticulum biogenesis.

An SRV-like virus was isolated from a colony-born Japanese monkey. To identify this SRV-like virus, we designed universal primers at regions that were conserved among the reported SRV sequences in the 59-LTR and the short ORF and we obtained plasmid clones containing the complete gag, prt, pol and env genes. The full-length sequences of the isolate were determined from the plasmids and by direct sequencing. Sequence comparisons and phylogenetic analyses indicated that this SRV-like virus had a sequence identical to the reported 626 bp of SRV-5. In this study, we isolated SRV5/JPN/2005/V1 from a Japanese monkey and characterized the fulllength SRV-5 sequence.Simian betaretroviruses (SRVs) (formerly known as simian type D retroviruses; SRV/Ds) have been isolated from Asian monkeys of the genus Macaca. SRVs are among the most important infectious agents in macaque colonies because SRVs cause immunodeficiency, anaemia, weight loss, tumours and persistent refractory diarrhoea (Daniel et al., 1984;Giddens et al., 1985;Lerche et al., 1987;Marx et al., 1984). Five distinct types of SRVs, SRV-1 through SRV-5, have been identified, based on neutralization tests. Furthermore, the complete DNA sequences of SRV-1, -2, -3 and -4, and the partial sequence of SRV-5 have been reported (Li et al., 2000; Power et al., 1986;Sonigo et al., 1986;Thayer et al., 1987;Zao et al., 2010). The serotype classifications for SRV-1 to SRV-5 have also been well supported by these phylogenetic analyses. Additionally, SRV-T, SRV-6 and SRV-7, have been identified, based on the results of phylogenetic analyses (Hara et al., 2005;Nandi et al., 2000Nandi et al., , 2006. SRV-T was reported as a virus strain of SRV-4 based on sequencing analysis (White et al., 2009;Zao et al., 2010).Only one SRV virus strain, D2/RHE/OR, has been isolated from a Japanese monkey (Macaca fuscata) at the Washington National Primate Research Center (Giddens et al., 1985). The D2/RHE/OR and closely related SRV-2 strains (SRV-2B) have also been identified in endemic infections of pig-tail monkeys (M. nemestrina), cynomolgus monkeys (M. fascicularis) and rhesus monkeys (M. mulatta) in the Washington and Oregon National Primate Research Center (Bryant et al., 1986;Grant et al., 1995;Hefti et al., 1983;Marracci et al., 1995 Marracci et al., , 1999 PhilippStaheli et al., 2006;Stromberg et al., 1984). In the present study, we isolated a novel SRV-5-like virus by culture from a Japanese monkey. We sequenced the complete proviral genome of this isolate and compared it with other known SRVs.Colony-born Japanese monkeys, J-03-001F1, J-04-067F1, J-07-005F1 and J-07-016F1, were bred and reared at a private monkey facility in Japan. As these animals showed persistent diarrhoea, anaemia and weight loss, the serum and EDTA-treated whole blood samples were sent to our laboratory for diagnosis. No PCR products were amplified from these samples using published primer sets that amplify SRV-1, -2, -3 or -4 (SRV-T) (Fujimoto et al., 2010;Liska et al., 1997) (data not shown). Virus isolation wa...