Abstract
We had previously shown that the transmembrane glycoprotein M6a, a member of the proteolipid protein (PLP) family, regulates neurite/filopodium outgrowth, hence, M6a might be involved in neuronal remodeling and differentiation. In this work we focused on M6, the only PLP family member present in Drosophila, and ortholog to M6a. Unexpectedly, we found that decreased expression of M6 leads to female sterility. M6 is expressed in the membrane of the follicular epithelium in ovarioles throughout oogenesis. Phenotypes triggered by M6 downregulation in hypomorphic mutants included egg collapse and egg permeability, thus suggesting M6 involvement in eggshell biosynthesis. In addition, RNAi-mediated M6 knockdown targeted specifically to follicle cells induced an arrest of egg chamber development, revealing that M6 is essential in oogenesis. Interestingly, M6-associated phenotypes evidenced abnormal changes of the follicle cell shape and disrupted follicular epithelium in mid- and late-stage egg chambers. Therefore, we propose that M6 plays a role in follicular epithelium maintenance involving membrane cell remodeling during oogenesis in Drosophila.
Highlights
The glycoprotein M6a was identified years ago, and despite its prominent expression in the central nervous system and other tissues [1,2], its biological function is still unknown
We found that M6 is expressed in the follicular epithelium of egg chambers throughout oogenesis in wild type flies
We focused on M601, which displayed clear fertility defects as homozygotes, while M602 were fertile and M603 were lethal
Summary
The glycoprotein M6a was identified years ago, and despite its prominent expression in the central nervous system and other tissues [1,2], its biological function is still unknown. In addition M6a plays an important role in neurite outgrowth and filopodium/spine formation [5], as well as in filopodium motility and likely synapse formation [6], suggesting that it might be involved in the plastic changes found in the hippocampus of stressed/antidepressant-treated animals. All of the PLP members have four transmembrane domains that allow their localization at the plasma membrane and are widely conserved along evolution from arthropods to mammals [9,10]. Other members of the PLP family such as M6b and DM20, but not PLP, are regulated by chronic stress, and were shown to be involved in neurite outgrowth and filopodium formation [11]. Members of the PLP family were proposed to interact with the actin cystoskeleton after their association with actin-enriched membranes [12]. PLP and DM20 were proposed to act as adhesion molecules [13], and M6a as an ion channel [14], underscoring that the molecular function of the PLP family remains undefined
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