View Program - 63rd Annual Drosophila Research Conference

Glial cells are crucial for many processes including providing structural support to neurons and for maintenance of the blood-brain/nerve-barrier (BBB). Permeability barriers are formed by septate junctions (SJ) in Drosophila to restrict diffusion of molecules across tissues. SJs comprise of many proteins including: NeurexinIV (NrxIV), Macroglobulin-complement-related (Mcr), kune-kune (k-k) and sinuous (sin). Barriers formed at the convergence of three SJ form the tricellular junction (TCJ) which include proteins like Anakonda, M6 and Gliotactin (Gli). A specific class of glia, the subperineurial glia (SPG), form auto-SJs with themselves and each other to create the BBB around the nervous system. Loss of a single core SJ or TCJ protein compromises the BBB leading to paralysis and lethality. While these junctions have been extensively studied in other tissues, their distribution and regulation in the nervous system is less studied. microRNA-184 (miR-184) is predicted to target a wide range of SJ and TCJ mRNAs. miR-184 targeting SJ proteins in epithelia was confirmed, however its role in nervous system is still unknown. While the presence of NrxIV is well established in glial SJ, we tested for distribution other SJ miR-184 targets within glia and established the presence of kune-kune, Mcr and sinous in glial SJs, and M6 and Gli in glial TCJs. miR-184 overexpression in SPG led to complete SJ and TCJ degradation and loss of these proteins from the membrane. Moreover, these larvae exhibited pupal lethality and decreased larval locomotion. In future, we will assess BBB integrity by dye penetration assays to understand the functional implication of SJ degradation. To determine which SJ mRNAs are affected by miR-184, we will quantify mRNA levels for each potential target using qRT-PCR. These results will reveal if miR-184 directly targets all SJ mRNAs predicted to be targets of miR-184, or just key SJ mRNAs which affect other SJ protein localization. A potential candidate for the latter possibility is NrxIV, which is a core protein that mediates SJ assembly. We will analyze the role played by NrxIV by testing if NrxIV mRNA lacking the miR-184 target sequence can rescue the SJ degradation phenotype. Our study will reveal the presence and regulation of key SJ proteins in SPG crucial for BBB maintenance. Degradation of permeability barriers in glia can result in a compromised BBB—a hallmark of many diseases across many species.

Regulation of Glial Septate Junction proteins by microRNA-184