Atypical septate junctions maintain the somatic enclosure around maturing spermatids and prevent premature sperm release inDrosophilatestis

Abstract

statement: Dubey et al., showed that septate junctions stitch the somatic 15 enclosure around maturing spermatids in Drosophila testis. Maintaining the integrity of 16 this junction is essential for proper release of spermatids. Abstract 20Tight junctions prevent the paracellular flow and maintain cell polarity in an epithelium. 21These are also essential for maintaining the blood-testis-barrier involved in regulating 22 sperm differentiation. Septate junctions are orthologous to the tight junctions in insects. 23In Drosophila testis, major septate junction components co-localize at the interface of 24 germline and somatic cells initially and then condense between the two somatic cells in 25 a cyst after germline meiosis. Their localization is extensively remodeled in subsequent 26 stages. We find that characteristic septate junctions are formed between the somatic cyst 27 cells at the elongated spermatid stage. Consistent with the previous reports, knockdown 28 of essential junctional components, Discs-large-1 and Neurexin-IV, in the somatic cyst 29 cells, during the early stages, disrupted sperm differentiation beyond the spermatocyte 30 stage. Somatic knockdown of these proteins during the final stages of spermatid 31 maturation caused premature release of spermatids inside the testes, resulting in partial 32 loss of male fertility. These results indicate the importance of maintaining mechanical 33 integrity of the somatic enclosure during spermatid coiling and release in Drosophila 34 testis. It also highlights the functional similarity with the tight junction proteins during 35 spermatogenesis in mammalian testes.36 37

Nanoscale indentation of plasma membrane establishes a contractile actomyosin scaffold through selective activation of the Amphiphysin-Rho1-Dia/DAAM and Rok pathway

“…These structural features resembled the tubulobulbar-complex found around individual spermatid heads inside Sertoli cells in mammalian testis (Guttman et al, 2004). Such tubules were not detected near the HCC-TCC interface (arrows, Fig 1H), which is held together by SJs (Dubey et al, 2019). Together, these analyses indicated that each spermatid is tightly ensleeved with the somatic cell membrane supported by F-actin (actin sleeve), and the head bundle (NB) is surrounded by a highly tubular actin-rich membrane, which we redefine as the 'basket' domain ( Fig 1A") (Video S1).…”

“…In Drosophila testis, 64 spermatids mature synchronously within a somatic cell enclosure formed by the head-cyst-cell (HCC) and tail-cyst-cell (TCC) that are held together by septate junction (SJ) proteins (Dubey et al, 2019). Each mature spermatid head is a rigid, ~10 µm long rod of ~200 nm diameter.…”

“…Rho1 recruits and activates nonmuscle myosin-II (NM2) through Rho-kinase (Rok). The actomyosin activity maintains the integrity of the actin-basket and holds the spermatid heads together in a parallel bundle, which is essential for maintaining male fertility (Dubey et al, 2019). Basket domain also prevents the penetration of the somatic cell by spermatid heads.…”

Long non-coding RNA regulation of spermatogenesis and endosomal processes via the spectrin cytoskeleton inDrosophila

“…Meanwhile, actin and specialized junctions are known to hold the sperm nuclei to the cyst cell 19,21 , but how the nuclei are drawn together into a tight bundle is still unknown. Similar to forces involved in the process of myoblast fusion where "Myoblast invasion triggers mechanosensitive accumulation of βH-Spectrin" 25 we see accumulation of βH-Spectrin at the site of spermatid penetration into the cyst (suggesting the actin cap may be similar to the brush border of the midgut).…”

“…Spermatogenesis requires dynamic remodeling of the actin-spectrin cytoskeleton in maturating sperm, cyst cells, and epithelial cells as the 64 sperm nuclei are brought together, condense into tight thin nuclei, elongate their tails, and remain held in a bundle within the cyst cells, which in turn have to migrate the length of the testis while interacting with the epithelial cells that make up the testis wall 16,17,18 . Although endosomal regulation of junctional complexes 19,20 and actin dynamics 21,22 play major roles in Drosophila spermatogenesis, how the complex cytoskeletal remodeling processes are tightly controlled in each interacting cell type during Drosophila spermatogenesis and bundling is still not completely understood. We demonstrate that the mutation in the lncRNA CR45362 gene disrupts the spermatid nuclear bundling process in Drosophila melanogaster.…”