Atypical septate junctions maintain the somatic enclosure around maturing spermatids and prevent premature sperm release in Drosophila testis

Mapping Intimacies ◽

10.1101/360115 ◽

2018 ◽

Author(s):

Pankaj Dubey ◽

Tushna Kapoor ◽

Samir Gupta ◽

Seema Shirolikar ◽

Krishanu Ray

Keyword(s):

Tight Junctions ◽

Somatic Cells ◽

Septate Junction ◽

Septate Junctions ◽

Discs Large ◽

Cyst Cells ◽

Drosophila Testis ◽

Summary Statement ◽

Premature Release ◽

Junction Proteins

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

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Gliotactin, a novel marker of tricellular junctions, is necessary for septate junction development in Drosophila

The Journal of Cell Biology ◽

10.1083/jcb.200303192 ◽

2003 ◽

Vol 161 (5) ◽

pp. 991-1000 ◽

Cited By ~ 89

Author(s):

Joost Schulte ◽

Ulrich Tepass ◽

Vanessa J. Auld

Keyword(s):

Tight Junctions ◽

Barrier Function ◽

Ultrastructural Analysis ◽

Mutant Phenotype ◽

Unique Function ◽

Septate Junction ◽

Septate Junctions ◽

Barrier Integrity ◽

Discs Large ◽

Dye Permeability

Septate junctions (SJs), similar to tight junctions, function as transepithelial permeability barriers. Gliotactin (Gli) is a cholinesterase-like molecule that is necessary for blood–nerve barrier integrity, and may, therefore, contribute to SJ development or function. To address this hypothesis, we analyzed Gli expression and the Gli mutant phenotype in Drosophila epithelia. In Gli mutants, localization of SJ markers neurexin-IV, discs large, and coracle are disrupted. Furthermore, SJ barrier function is lost as determined by dye permeability assays. These data suggest that Gli is necessary for SJ formation. Surprisingly, Gli distribution only colocalizes with other SJ markers at tricellular junctions, suggesting that Gli has a unique function in SJ development. Ultrastructural analysis of Gli mutants supports this notion. In contrast to other SJ mutants in which septa are missing, septa are present in Gli mutants, but the junction has an immature morphology. We propose a model, whereby Gli acts at tricellular junctions to bind, anchor, or compact SJ strands apically during SJ development.

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Septate junctions mediate the barrier to paracellular permeability in sea urchin embryos

Zygote ◽

10.1017/s096719940500328x ◽

2005 ◽

Vol 13 (3) ◽

pp. 255-264 ◽

Cited By ~ 12

Author(s):

Erin M. Itza ◽

Nancy M. Mozingo

Keyword(s):

Tight Junctions ◽

Sea Urchin ◽

Divalent Cations ◽

Paracellular Permeability ◽

Septate Junction ◽

Septate Junctions ◽

Permeability Characteristics ◽

Sea Urchin Embryos ◽

Cell Layers ◽

Junction Structure

In sea urchin embryos, blastula formation occurs between the seventh and tenth cleavage and is associated with changes in the permeability properties of the epithelium although the structures responsible for mediating these changes are not known. Tight junctions regulate the barrier to paracellular permeability in chordate epithelia; however, the sea urchin blastula epithelium lacks tight junctions and instead possesses septate junctions. Septate junctions are unique to non-chordate invertebrate cell layers and have a characteristic ladder-like appearance whereby adjacent cells are connected by septa. To determine the function of septate junctions in sea urchin embryos, the permeability characteristics of the embryonic sea urchin epithelia were assessed. First, the developmental stage at which a barrier to paracellular permeability arises was examined and found to be in place after the eighth cleavage division. The mature blastula epithelium is impermeable to macromolecules; however, brief depletion of divalent cations renders the epithelium permeable. The ability of the blastula epithelium to recover from depletion of divalent cations and re-establish a barrier to paracellular permeability using fluorescently labelled lectins was also examined. Finally, septate junction structure was examined in embryos in which the permeability status of the epithelium was known. The results provide evidence that septate junctions mediate the barrier to paracellular permeability in sea urchin embryos.

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A freeze-fracture and lanthanum tracer study of the complex junction between Sertoli cells of the canine testis.

The Journal of Cell Biology ◽

10.1083/jcb.76.1.57 ◽

1978 ◽

Vol 76 (1) ◽

pp. 57-75 ◽

Cited By ~ 56

Author(s):

C J Connell

Keyword(s):

Tight Junctions ◽

Sertoli Cells ◽

Freeze Fracture ◽

Intercellular Junctions ◽

Septate Junction ◽

Septate Junctions ◽

Thin Sections ◽

En Face ◽

Lanthanum Tracer ◽

Complex Junction

What appear to be true septate junctions by all techniques currently available for the cytological identification of intercellular junctions are part of a complex junction that interconnects the Sertoli cells of the canine testis. In the seminiferous epithelium, septate junctions are located basal to belts of tight junctions. In thin sections, septate junctions appear as double, parallel, transverse connections or septa spanning an approximately 90-A intercellular space between adjacent Sertoli cells. In en face sections of lanthanum-aldehyde-perfused specimens, the septa themselves exclude lanthanum and appear as electron-lucent lines arranged in a series of double, parallel rows on a background of electron-dense lanthanum. In freeze-fracture replicas this vertebrate septate junction appears as double, parallel rows of individual or fused particles which conform to the distribution of the intercellular septa. Septate junctions can be clearly distinguished from tight junctions as tight junctions prevent the movement of lanthanum tracer toward the lumen, appear as single rows of individual or fused particles in interlacing patterns within freeze-fracture replicas, and are seen as areas of close membrane apposition in thin sections. Both the septate junction and the tight junction are associated with specializations of the Sertoli cell cytoplasm. This is the first demonstration in a vertebrate tissue of a true septate junction.

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Faculty Opinions recommendation of Analysis of protein dynamics within the septate junction reveals a highly stable core protein complex that does not include the basolateral polarity protein Discs large.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717955669.793460673 ◽

2012 ◽

Author(s):

Yang Hong

Keyword(s):

Protein Dynamics ◽

Protein Complex ◽

Core Protein ◽

Septate Junction ◽

Discs Large ◽

Stable Core

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Expanding the Junction: New Insights into Non-Occluding Roles for Septate Junction Proteins during Development

Journal of Developmental Biology ◽

10.3390/jdb9010011 ◽

2021 ◽

Vol 9 (1) ◽

pp. 11

Author(s):

Clinton Rice ◽

Oindrila De ◽

Haifa Alhadyian ◽

Sonia Hall ◽

Robert E. Ward

Keyword(s):

Drosophila Melanogaster ◽

Barrier Function ◽

Septate Junction ◽

Accessory Proteins ◽

Organ Function ◽

The Past ◽

Core Components ◽

Developmental Contexts ◽

Mechanistic Understanding ◽

Junction Proteins

The septate junction (SJ) provides an occluding function for epithelial tissues in invertebrate organisms. This ability to seal the paracellular route between cells allows internal tissues to create unique compartments for organ function and endows the epidermis with a barrier function to restrict the passage of pathogens. Over the past twenty-five years, numerous investigators have identified more than 30 proteins that are required for the formation or maintenance of the SJs in Drosophila melanogaster, and have determined many of the steps involved in the biogenesis of the junction. Along the way, it has become clear that SJ proteins are also required for a number of developmental events that occur throughout the life of the organism. Many of these developmental events occur prior to the formation of the occluding junction, suggesting that SJ proteins possess non-occluding functions. In this review, we will describe the composition of SJs, taking note of which proteins are core components of the junction versus resident or accessory proteins, and the steps involved in the biogenesis of the junction. We will then elaborate on the functions that core SJ proteins likely play outside of their role in forming the occluding junction and describe studies that provide some cell biological perspectives that are beginning to provide mechanistic understanding of how these proteins function in developmental contexts.

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Topographical variations in the structure of the smooth septate junction

Journal of Cell Science ◽

10.1242/jcs.37.1.373 ◽

1979 ◽

Vol 37 (1) ◽

pp. 373-389

Author(s):

H.B. Skaer ◽

J.B. Harrison ◽

W.M. Lee

Keyword(s):

Musca Domestica ◽

Functional Significance ◽

Freeze Fracture ◽

Rhodnius Prolixus ◽

Malpighian Tubules ◽

Septate Junction ◽

Lanthanum Hydroxide ◽

Septate Junctions ◽

Standard Fixation

Smooth septate junctions in the midgut of Musca domestica and in Malpighian tubules of both Musca and Rhodnius prolixus are described. Details of the structures revealed after standard fixation, fixation in the presence of the stain, lanthanum hydroxide, and after freeze-fracture are discussed in the light of models previously put forward to explain the interrelations of the images obtained by these different methods. The organization of the junction between cells of the midgut varies in the apical-to-basal axis. At the apical border the septa (or ridges in freeze-fracture replicas) are packed tightly and follow an undulating but strictly parallel course. This packing loosens towards the middle of the junction until, at its basal extremity, the septa (ridges in replicas) are widely separated and follow independent meandering courses. That these features are found both in lanthanum-infiltrated specimens and freeze-fracture replicas allows a correlation to be made between the septa and the freeze-fracture ridges. The functional significance of these smooth septate junctions is discussed.

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Assembly of C. elegans apical junctions involves positioning and compaction by LET-413 and protein aggregation by the MAGUK protein DLG-1

Journal of Cell Science ◽

10.1242/jcs.114.12.2265 ◽

2001 ◽

Vol 114 (12) ◽

pp. 2265-2277 ◽

Cited By ~ 7

Author(s):

Laura McMahon ◽

Renaud Legouis ◽

Jean-Luc Vonesch ◽

Michel Labouesse

Keyword(s):

Essential Gene ◽

Critical Role ◽

Septate Junction ◽

C Elegans ◽

Tissue Integrity ◽

Discs Large ◽

Genes Encoding ◽

Strong Adhesion ◽

Junctional Protein ◽

Apical Junctions

Specialised subapical junctions play a critical role in maintaining epithelial cell polarity and tissue integrity, and provide a platform for intracellular signalling. Here we analyse the roles of C. elegans genes let-413 and dlg-1, a homologue of Drosophila lethal discs large, in the assembly of the C. elegans apical junction (CeAJ), and provide the first characterisation of this structure. We have identified dlg-1 as an essential gene in an RNA interference screen against C. elegans homologues of genes encoding proteins involved in tight or septate junction formation. We show that DLG-1 colocalises with the junctional protein JAM-1 at CeAJs in a unit distinct from HMP-1/α-catenin, and apical to the laterally localised LET-413. Loss of dlg-1 activity leads to JAM-1 mislocalisation and the disappearance of the electron-dense component of the CeAJs, but only mild adhesion and polarity defects. In contrast, loss of let-413 activity leads to the formation of basally extended discontinuous CeAJs and strong adhesion and polarity defects. Interestingly, in LET-413-deficient embryos, CeAJ markers are localised along the lateral membrane in a manner resembling that observed in wild-type embryos at the onset of epithelial differentiation. We conclude that the primary function of LET-413 is to correctly position CeAJ components at a discrete subapical position. Furthermore, we propose that DLG-1 is required to aggregate JAM-1 and other proteins forming the electron-dense CeAJ structure. Our data suggest that epithelial adhesion is maintained by several redundant systems in C. elegans.

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Isolation and biochemical characterization of septate junctions: differences between the proteins in smooth and pleated varieties

Journal of Cell Science ◽

10.1242/jcs.93.1.123 ◽

1989 ◽

Vol 93 (1) ◽

pp. 123-131

Author(s):

NANCY J. LANE ◽

STEPHEN M. DILWORTH

Keyword(s):

Periplaneta Americana ◽

Biochemical Characterization ◽

Septate Junction ◽

Septate Junctions ◽

Molecular Weights ◽

Thin Sectioning ◽

Sds Page ◽

High Concentrations ◽

Membrane Components

Septate junctions are found only in invertebrate tissues, and are almost ubiquitous within them. In arthropods, the two major types are the ‘pleated’ and the ‘smooth’ varieties. Using tissues from different species, including the cockroach Periplaneta americana, procedures have been established for obtaining membrane fractions selectively enriched in septate junctions. The junctions have been identified in pellets of these fractions by both thin sectioning and freeze-fracturing. SDS-PAGE of these membrane fractions reveals two major polypeptide species with apparent molecular weights of 22000–24000 and 17000–18000. Consistent differences in these apparent molecular weights are observed between the pleated and smooth varieties of septate junction. These polypeptides are probably integral membrane components, as they remain associated after treatment with high concentrations of urea. Evidence suggests a plane of weakness in the mid-line of the extracellular septal ribbons.

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