Somatic mesodermal specification produces three different types of myoblasts.
The Drosophila melanogaster larval body wall muscles are established during embryogenesis beginning with the invagination of the mesoderm, which spreads along the ectoderm and then forms numerous mesodermal derivatives ( Dobi et al., 2015 ). We propose that dNedd4Lo destabilizes dAmph in muscles, leading to impaired T-tubule formation and muscle function. This effect was not seen in muscles expressing dNedd4S or a catalytically-inactive dNedd4Lo(C→A). Moreover, expression of dNedd4Lo in muscle during embryonic development led to disappearance of dAmph and impaired T-tubule formation, phenocopying amph-null mutants. Accordingly, dNedd4Lo was colocalized with dAmph postsynaptically and at muscle T-tubules. We validated the interaction by coimmunoprecipitation and showed direct binding between dAmph-SH3 domain and dNedd4Lo N-terminus.
dAmph is a postsynaptic protein containing SH3-BAR domains and regulates muscle transverse tubule (T-tubule) formation in flies. To delineate the cause of the impaired locomotion, we searched for binding partners to the N-terminal unique region of dNedd4Lo in larval lysates using mass spectrometry and identified Amphiphysin (dAmph). We previously showed that whereas dNedd4S promotes neuromuscular synaptogenesis, dNedd4Lo inhibits it and impairs larval locomotion. DNedd4Lo has a unique N-terminus containing a Pro-rich region. Drosophila Nedd4 (dNedd4) is a HECT ubiquitin ligase with two main splice isoforms: dNedd4-short (dNedd4S) and -long (dNedd4Lo).
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