Tubulin-binding cofactor E-like (TBCEL), the protein product of the mulet gene, is required in the germline for the regulation of inter-flagellar microtubule dynamics during spermatid individualization

• Published in: Biology open 2020-01
• Main Authors: Fabrizio, J J, Rollins, J, Bazinet, C W, Wegener, S, Koziy, I, Daniel, R, Lombardo, V, Pryce, D, Bharrat, K, Innabi, E, Villanobos, M, Mendoza, G, Ferrara, E, Rodway, S, Vicioso, M, Siracusa, V, Dailey, E, Pronovost, J, Innabi, S, Patel, V, DeSouza, N, Quaranto, D, Niknejad, A
• Format: Article
• Language: English
• ISSN: 2046-6390

Individual sperm cells are resolved from a syncytium during late step of spermiogenesis known as individualization, which is accomplished by an Individualization Complex (IC) composed of 64 investment cones. mulet encodes Tubulin-binding cofactor E-like (TBCEL), suggesting a role for microtubule dynamics in individualization. Indeed, a population of ∼100 cytoplasmic microtubules fails to disappear in mulet mutant testes during spermatogenesis. This persistence, detected using epi-fluorescence and electron microscopy, suggests that removal of these microtubules by TBCEL is a prerequisite for individualization. Immunofluorescence reveals TBCEL expression in elongated spermatid cysts. In addition, testes from mulet mutant males were rescued to wild-type using tubulin-Gal4 to drive TBCEL expression, indicating that the mutant phenotype is caused by the lack of TBCEL. Finally, RNAi driven by bam-GAL4 successfully phenocopied mulet, confirming that mulet is required in the germline for individualization. We propose a model in which the cytoplasmic microtubules serve as alternate tracks for investment cones in mulet mutant testes.