Dornan, A. J. | bioRxiv Science

bioRxiv2020

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

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 tubules 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. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/422678v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@68e080org.highwire.dtl.DTLVardef@16af9ddorg.highwire.dtl.DTLVardef@3a399eorg.highwire.dtl.DTLVardef@9cc393_HPS_FORMAT_FIGEXP M_FIG Model for epithelial dysfunction arising from failure of smooth septate junctional complexes as a consequence of impaired Snakeskin expression. C_FIG

physiology↗

bioRxiv2019

When two cells are better than one: specialized stellate cells provide a privileged route for uniquely rapid water flux in Drosophila renal tubule

Insects are highly successful, in part through an excellent ability to osmoregulate. The renal (Malpighian) tubules can secrete fluid faster on a per-cell basis than any other epithelium, but the route for these remarkable water fluxes has not been established. In Drosophila melanogaster, we show that 4 members of the Major Intrinsic Protein family are expressed at very high level in the fly renal tissue; the aquaporins Drip and Prip, and the aquaglyceroporins Eglp2 and Eglp4. As predicted from their structure and by their transport function by expressing these proteins in Xenopus oocytes, Drip, Prip and Eglp2 show significant and specific water permeability, whereas Eglp2 and Eglp4 show very high permeability to glycerol and urea. Knockdowns of any of these genes impacts tubule performance resulting in impaired hormone-induced fluid secretion. The Drosophila tubule has two main secretory cell types: active cation-transporting principal cells with the aquaglyceroporins localize to opposite plasma membranes and small stellate cells, the site of the chloride shunt conductance, with these aquaporins localising to opposite plasma membranes. This suggests a model in which cations are pumped by the principal cells, causing chloride to follow through the stellate cells in order to balance the charge. As a consequence, osmotically obliged water follows through the stellate cells. Consistent with this model, fluorescently labelled dextran, an in vivo marker of membrane water permeability, is trapped in the basal infoldings of the stellate cells after kinin diuretic peptide stimulation, confirming that these cells provide the major route for transepithelial water flux. The spatial segregation of these components of epithelial water transport may help to explain the unique success of the higher insects.\n\nSignificance statementThe tiny insect renal (Malpighian) tubule can transport fluid at unparalleled speed, suggesting unique specialisations. Here we show that strategic allocation of Major Intrinsic Proteins (MIPs) to specific cells within the polarized tubule allow the separation of metabolically intense active cation transport from chloride and water conductance. This body plan is general to at least many higher insects, providing a clue to the unique success of the class Insecta.

physiology↗