The AbdB – Boss/Sev – integrin cascade: cell autonomous and cell non-autonomous effects in larval stem cell niche positioning and function 3.2.1. Abd-B target genes revealed that Abd-B mediates its effects by controlling the activity of the sevenless ligand Boss via its direct targets and larvae testis, Integrin, Talin, Niche positioning 1.?Introduction genes are master regulators of morphogenesis that code for homeodomain-containing transcription factors with a high conservation in different metazoans. Studying their function during embryogenesis in animals as diverse as insects and vertebrates revealed their critical role in establishing the identity of segmental structures along the anterior-posterior (A/P) body axis of these organisms . More recent research emphasizes the role of genes as cell-type switches [8,55,79] that control local cell behaviors resulting in the development of segment-specific structures and organs [3,43,66]. genes are expressed throughout an animal’s life , suggesting that they control different aspects of morphogenesis in a stage-dependent manner. However, due to the deleterious effects of gene mutations, which normally result in the death of the organism at the end of embryogenesis, later Hox functions have rarely been studied [2,61,62,74]. Even more important, it has not been successfully Refametinib (RDEA-119, BAY 86-9766) addressed if Refametinib (RDEA-119, BAY 86-9766) and how genes control the development and maintenance of structures and organs throughout the life of an organism, from embryogenesis to adulthood when new cell types and interactions emerge in the various stages. To answer this question, we use the fruitfly male stem cell niche is maintained after its initial specification, we review the current state of the art on stage-specific niche architecture and function, and explain how the posterior Refametinib (RDEA-119, BAY 86-9766) Hox gene controls, as an upstream regulator, niche positioning and integrity in a cell-type and stage specific way. 2.?testis and the male stem cell niche In all adult tissues harboring stem cells, the stem cell niche has a critical function as an organizer, which recruits the stem cells and provides the microenvironment required for stem cell maintenance. Much of the knowledge we have on testis stem cells and their niche comes from studies in testis, a structure first made by the coalesce of germ cells and somatic gonadal cells at stage 14 of embryogenesis, continues throughout embryonic and larval stages, and goes through a second wave of organ shaping in the pupae, to reach maturation in adult stages. The male stem cell niche, called the hub, is a cluster of non-dividing cells specified in the anterior most somatic gonadal cells already before gonad coalesce [4,20,21,25,40,53]. The first signs of testis organogenesis are already detected in late embryogenesis (stages 14-17), once the specified hub cells recruit the anterior-most germ cells to become the germline stem cells (GSCs) . A testis with a mature stem cell niche and all pre-meiotic stages is detected at 3rd instar larvae (L3) (Fig.?1A). The testis contains two types of stem cells: the germline stem cells (GSCs) and the somatic Rabbit Polyclonal to STK39 (phospho-Ser311) cyst stem cells (CySCs). Each GSC is flanked by two somatic cyst stem cells (CySCs) and both types of stem cells are maintained through their association to the hub cells, a cluster of non-dividing cells forming the niche organizer. Upon asymmetric cell division, each GSC produces a new GSC attached to the hub and a distally located gonialblast. The CySCs also divide asymmetrically to generate a CySC remaining associated with the hub and a distally located post-mitotic daughter somatic cyst cell (SCC) . Two SCCs enclose each gonialblast forming a testicular cyst sealed from the outside by the extracellular matrix (ECM) (Fig.?1) . The gonialblast divides mitotically four more times to give rise to 16 interconnected spermatogonial cells, which then undergo pre-meiotic DNA replication, become spermatocytes, turn on the transcription program for terminal differentiation and undergo meiosis. During pupal stages testis morphogenesis is completed with the addition of the acto-myosin sheath originating from the genital disc . The SCCs co-differentiate with the germ cells they enclose, grow enormously in size, elongate and accompany them throughout their differentiation steps up to individualization and sperm production in the adult testis . Open in a separate window Fig.?1 (A) Diagram showing the stem cell niche and early stages of spermatogenesis. GSC: germline stem cell, CySC: Refametinib (RDEA-119, BAY 86-9766) somatic.