The internal structure of embryonic gonads and testis development in Drosophila melanogaster requires scrib, lgl and dlg activity in the soma

Abstract

Interest in the mechanism leading to the formation of the germline and its differentiation during Drosophila development, initiated even as soon as the first ever cloned tumour suppressor gene in Drosophila, the lethal (2) giant larvae (lgl), had been identified. Further work has shown that the lgl, as well as discs large-1 (dlg) and scribble (scrib) tumor suppressor genes code for scaffolding proteins associated with either the cytoskeletal matrix or the septate junctions that act in common pathways in various tissues. This study analysed the role of Dlg, Scrib and Lgl in the embryonic gonads and testis of Drosophila melanogaster. Loss of scrib, dlg and lgl had no effect on gonad formation, but Dlg and Scrib in the gonadal mesoderm acted critically in the somatic wrapping of the pole cells and the internal structure of the Drosophila embryonic gonads. Dlg also affected the incorporation of the male-specific Sox100B positive mesodermal cells into the male embryonic gonads, yet Sox100B expression in dlg testis remained unaffected. Analysis at later stages revealed that scrib and lgl expression in the somatic lineage of the Drosophila testis, similar to what was previously shown for dlg, was indispensable for testis development and homeostasis, as depletion of these genes resulted in extensive testes defects. The data presented here emphasize the somatic requirement of Scrib, Dlg and Lgl in embryonic gonads, as well as in the Drosophila testis that underlines the importance of the somatic lineage in the establishment and maintenance of testis formation throughout successive developmental stages.

The Male Stem Cell Niche: Insights from Drosophila and Mammalian Model Systems

“…scrib is expressed in the somatic gonadal cells of the newly formed embryonic Drosophila gonads [101,102] and analysis of agametic gonads and pseudo-gonads made of aggregated germ cells confirmed this observation [102]. Analysis of scrib and dlg mutant gonads revealed that the gonadal mesodermal cells are not able to extend projections between the germ cells suggesting a role in establishing the intimate contacts of the gonadal mesoderm to the germ cells [93,102]. At larval stages, dlg, scrib and lgl expression in the somatic lineage is indispensable for testis homeostasis and spermatogenesis, as depletion of these genes results in extremely small testes with reduced number of GSCs, increased number of early cyst cells (positive for early cyst cell marker Traffic-Jam), impaired differentiation and infertility.…”

“…All these studies on the role of septate junction components in the Drosophila testis, underline the importance of the CySCs and SCCs to encapsulate the germline and establish the cyst integrity, which is necessary for germline differentiation and normal testis function to finally produce healthy sperm and ensure fertility [10,89,93]. Interestingly, the Drosophila testis cyst cells show striking similarities with the Sertoli cells, the supportive cells of the mammalian germline, in terms of cytoskeletal and scaffolding components [10].…”

“…Late cyst cells and their corresponding spermatocyte cysts are lost via apoptosis in dlg testes [88]. Similar to dlg, lgl testes also lose late cyst cells, whereas in scrib testes late cyst cells are still present albeit with a significantly reduced nucleus size [93]. Rescue experiments expressing a dlg transgene in cyst cells could restore normal testis morphology and function.…”

“…Critical cytoskeletal and polarity components localize at cyst cells, such as Rho1, Rac1 [84], Profilin (encoded by the chickadee/chic gene) [58,92], βPS-Integrin (encoded by the myospheroid gene) [28], Talin (encoded by the rhea gene) [42], as well as the septate junction components Neurexin-IV (Nrx-IV), Coracle (Cora) [92], Discs large (Dlg), Scribble (Scrib) and Lethal (2) giant larvae (Lgl) [88,93]. Septate junctions (SJ) (the equivalent of vertebrate Tight Junctions) are primary candidates for cyst integrity and coordination, as apart from acting as sealing junctions in epithelia and neurons by mediating cell-cell adhesion, they act as scaffolding networks together with multiple pathways to promote organ morphogenesis [94].…”

“…Septate junctions (SJ) (the equivalent of vertebrate Tight Junctions) are primary candidates for cyst integrity and coordination, as apart from acting as sealing junctions in epithelia and neurons by mediating cell-cell adhesion, they act as scaffolding networks together with multiple pathways to promote organ morphogenesis [94]. The last years a number of studies addressed the role of septate junction components in the testicular cyst integrity, spermatogenesis and testis homeostasis [58,88,92,93]. These include studies analyzing the critical role of the Drosophila Profilin and septate junctional core components Nrx-IV and Cora [58,92] in germline encapsulation by the cyst cells.…”