title: Accumulation of a differentiation regulator specifies transit amplifying division number in an adult stem cell lineage.
abstract: 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. The Drosophila Bag of Marbles (Bam) protein is required for male germ cells to cease spermatogonial TA divisions and initiate spermatocyte differentiation [McKearin DM, et al. (1990) Genes Dev 4:2242-2251]. Contrary to models involving dilution of a differentiation repressor, our results suggest that the switch from proliferation to terminal differentiation is triggered by accumulation of Bam protein to a critical threshold in TA cells and that the number of TA divisions is set by the timing of Bam accumulation with respect to the rate of cell cycle progression.
authors.affiliation: Department of Developmental Biology, Stanford University School of Medicine, Beckman Center B300, 279 Campus Drive, Stanford, CA 94305-5329, USA. minsco@stanford.edu
authors.forename: Megan L
authors.initials: ML
authors.lastname: Insco
authors.forename: Arlene
authors.initials: A
authors.lastname: Leon
authors.forename: Cheuk Ho
authors.initials: CH
authors.lastname: Tam
authors.forename: Dennis M
authors.initials: DM
authors.lastname: McKearin
authors.forename: Margaret T
authors.initials: MT
authors.lastname: Fuller
mesh_terms: D053687:Adult Stem Cells / Q000166:cytology* / Q000378:metabolism*; D000818:Animals; D030801:Animals, Genetically Modified; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D002455:Cell Division / Q000235:genetics / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D017344:Genes, Insect; D008297:Male; D008954:Models, Biological; D013090:Spermatocytes / Q000166:cytology / Q000378:metabolism; D013091:Spermatogenesis / Q000235:genetics / Q000502:physiology; D013093:Spermatogonia / Q000166:cytology / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; C091674:bam protein, Drosophila