The enclosed gonialblast first proliferates by transit amplifying divisions (TA-divisions), which are a characteristic feature observed in most stem cell daughter populations. The cyst cells grow in size and continue to enclose the germline cells ( Figures 1A, 1B) as they develop from early-stage cyst cells into late-stage cyst cells based on the size of their nuclei and the expression of stage specific molecular markers. The cyst (composed of germline and two surrounding cyst cells) then undergoes a highly coordinated differentiation program. During this process, two cyst cells grow cytoplasmic extensions around one newly formed gonialblast, –. Once produced, cyst cells normally cease mitosis and form the germline microenvironment. Both stem cell populations undergo asymmetric mitotic cell divisions, producing gonialblasts and cyst cells respectively. The germline stem cells (GSCs) are attached to a single group of post-mitotic, apical hub cells and enclosed by cytoplasmic extensions from two somatic stem cells, the cyst stem cells (CySCs, Figure 1A). Within the Drosophila testis, the germline cells and their somatic support cells are arranged in a spatio-temporal order along the apical to basal axis. One of the best described examples of the dependence of a stem cell lineage on another cell type is the development of germline cells in the male gonad of Drosophila melanogaster. Also in the skin, follicular stem cell activation is regulated by signals from underlying intradermal adipocytes, and in the bone marrow, hematopoietic stem cell fate and proliferation depend on mesenchymal stem cells –. For example, in the hair follicle of the skin, melanocyte stem cells are closely associated with epithelial stem cells and signaling between the two lineages is an important mechanism in coordinating the differentiation of the two stem cell lineages to make pigmented hair. Self-renewal of stem cells and differentiation of stem cell daughters are regulated by interactions with other cell types. Tissue homeostasis depends on adult stem cells that constantly self-renew and produce differentiated cells.

The funders have no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. (no grant #), and start-up funds from University of Georgia, Athens, and NSF grant #0841419 given to C.S. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: The work was supported by a grant from the American Foundation for Aging Research given to B.B.P. Received: MaAccepted: JPublished: August 5, 2013Ĭopyright: © 2013 Hudson et al. PLoS ONE 8(8):Įditor: Andreas Bergmann, University of Massachusetts Medical School, United States of America We propose that as the cysts develop, a temporal signature of EGF signaling is created by the coordinated increase of both the production of active ligands by the germline cells and the amount of available receptor molecules on the cyst cells.Ĭitation: Hudson AG, Parrott BB, Qian Y, Schulz C (2013) A Temporal Signature of Epidermal Growth Factor Signaling Regulates the Differentiation of Germline Cells in Testes of Drosophila melanogaster. Terminal differentiation was promoted in testes expressing a constitutively active EGF Receptor (EGFR) and in testes expressing both a secreted EGF and the EGFR in the cyst cells, but not in testes expressing either only EGF or only EGFR. In addition to the previously reported requirement for EGF signaling in cyst formation, a low dose of EGF signaling is required for the progression of the germline cells through transit amplifying divisions, and a high dose of EGF signaling promotes terminal differentiation. By characterizing flies with reduced or increased Epidermal Growth Factor (EGF) signaling we show that EGF triggers different responses in the cysts dependent on its dose. In Drosophila testes, somatic cyst cells enclose the proliferating and differentiating germline cells and the units of germline and surrounding cyst cells are commonly referred to as cysts. Here we address how stem cell daughters are guided through the early steps of development. Tissue replenishment from stem cells follows a precise cascade of events, during which stem cell daughters first proliferate by mitotic transit amplifying divisions and then enter terminal differentiation.

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