<i>Drosophila</i> ryanodine receptor gene triggers functional and developmental muscle properties and could be used to assess the impact of human <i>RYR1</i> mutations.

Abstract

The ryanodine receptor (RYR) genes encode evolutionarily conserved calcium release channels involved in a wide range of calcium-dependent biological processes. Here, we show that the sole <i>Drosophila</i> RYR gene (<i>dRyR</i>) functions in differentiated somatic and cardiac muscle as well as in developing embryonic myotubes. In the larval body wall muscles, dRyR protein localizes at the SR membranes, and <i>dRyR</i> knockdown adversely affects muscle contractility, suggesting its conserved role in calcium-triggered E-C coupling. After <i>dRyR</i> attenuation, sarcomere, and mitochondrial patterns are severely impaired, showing <i>dRyR</i> involvement in structural muscle properties. However, <i>dRyR</i> is also prominently expressed and functionally required in growing embryonic muscles. <i>dRyR</i> loss of function leads to myotube growth defects and thin myofiber phenotypes, while its overexpression induces myofiber splitting. Given the structural and functional conservation of <i>dRyR</i>, we used <i>Drosophila</i> to test the impact of one human <i>RYR1</i> variant of unknown significance (VUS). Larvae carrying <i>p.Met4881Ile RYR1</i> VUS showed impaired mobility and altered structural muscle properties reminiscent of those seen in <i>dRyR</i> knockdown, thus indicating it is likely pathogenic. Overall, we show that <i>Drosophila dRyR</i> plays a conserved role in setting muscle contractility and structural muscle features. Our findings underline the still under-investigated role of <i>dRyR</i> as a promyogenic factor and provide a first example of the impact assessment of a human <i>RYR1</i> VUS in <i>Drosophila</i>.