The septate junction protein Snakeskin is critical for epithelial barrier function and tissue homeostasis in the Malpighian tubules of adultDrosophila

Abstract

Transporting epithelia provide a protective physical barrier while directing appropriate transport of ions, solutes and water. In invertebrates, epithelial integrity is dependent on formation, and maintenance, of ′tight′ septate junctions (SJs). We demonstrated that Drosophila Malpighian (renal) tubules undergo an age-dependent decline in secretory transport capacity, which correlates with mislocalisation of SJ proteins and coincident progressive degeneration in cellular morphology and tissue homeostasis. By restrictively impairing, in adult tubules, the cell adhesion protein Snakeskin, which is essential for smooth SJ formation, we observed progressive changes in cellular and tissue morphology that phenocopied these effects, including mislocalisation of junctional proteins with concomitant loss of cell polarity and barrier function. Resulting in significant accelerated decline in tubule secretory capacity and organismal viability. Our investigations highlight the tubule′s essential role in maintenance of organismal health, while providing measurable markers of compromised epithelial barrier and tissue function that manifest in advanced morbidity and death.

Updates on ion and water transport by the Malpighian tubule

“…Knockdown of known septate junction proteins Mesh [ 41 ] or Tetraspanin 2A [ 42 ] in tubule principal cells results in measurably leaky epithelia with compromised fluid secretion and bloated phenotype. Similar effects were seen with knockdown of Snakeskin , encoding another junctional protein [ 43 ]. Additionally, progressive disruption in epithelial organisation was observed with aging [ 43 ].…”

“…Similar effects were seen with knockdown of Snakeskin , encoding another junctional protein [ 43 ]. Additionally, progressive disruption in epithelial organisation was observed with aging [ 43 ]. The overall impression therefore, is that the septate junction is indeed a functional analogue of the vertebrate tight junction, and that its barrier function is necessary to allow successful secretion.…”

A cell atlas of the fly kidney

“…S6A and S6B). This contrasts with knockdown of Ssk, which caused loss of both cytoarchitectural organization and septate junctions (Dornan et al, 2020). Finally, knockdown of other top marker genes, namely Prip , Frequenin 2 ( Frq2 ) and CG10939, did not affect the septate junctions (Fig.…”

“…As the PC and SC lineages have distinct origins (ectodermal and mesodermal, respectively) (Denholm et al, 2003), they might not necessarily form heterotypic junctions. In fact, both cell types express the septate (occluding) junctional genes discs large 1 ( dlg1 ), snakeskin ( ssk ) (Dornan et al, 2020) and Mesh (Jonusaite et al, 2020) throughout the length of the tubule, suggesting that both PC-PC and PC-SC junctions are equally tight. Interestingly, although both cell types also contribute adherens junction components, the emphasis is different, with polychaetoid ( ZO-1/pyd ) emphasized by SCs and Armadillo ( arm ) by PCs.…”

“…Previous studies have shown that disruption of SCs affects fly survival. For example, conditional downregulation of Rab11 in SCs results in lethality at the pharate adult stage, and knockdown of Snakeskin ( Ssk ) in SCs result in loss of fluid integrity and a significant reduction in viability (Choubey et al, 2020; Dornan et al, 2020). Furthermore, ablation of SCs causes lethality, confirming the essential role of this cell type (Denholm et al, 2003).…”