| Microtubules are one of the three major cytoskeletal proteins in cells.They participate in cellular activities such as cell division,differentiation,migration,material transport,and damage repair.The diversity of microtubule functions relies on a variety of microtubule regulatory proteins.Nearly 500 microtubule-associated proteins and about 50 microtubule post-translational modification enzymes have been discovered.These proteins regulate microtubule polymerization,depolymerization,severing,and stability.Apparently,a cell type uses only a small fraction of these microtubule regulatory proteins at a specific state.It is still unclear how different cell types choose a specific set of microtubule-related proteins to fulfill their functions.In this paper,we used the LNv clock neurons in the Drosophila brain as a model to study the functions of different microtubule-associated proteins.LNv neurons drive the circadian behavior of Drosophila and are easy to label,simple in shape and structure,and easy to quantify its morphological changes.We examined a variety of microtubule-stabilizing proteins,severing proteins,and post-translational modification proteins.This revealed that the microtubule stabilizing proteins TBCE and Tau,and the microtubule severing protein Spas regulate the morphology of LNv neurons.We further found that the morphology of LNv neurons was sensitive to the expression levels of Spas: short-term expression of Spas caused axon overgrowth,while long-term expression resulted in axon atrophy.These results suggest that wellbalanced dynamics of the microtubules are essential for the morphological development of the LNv neurons.Interestingly,overexpression or knockdown of another microtubule severing protein Kat 60 did not affect the morphology of LNv neurons.Overexpression of Kat60 in the muscle cells of Drosophila larvae broke down the microtubule network;overexpression of Kat 60 in sensory neurons of Drosophila larvae also caused morphological defects.These results suggest that LNv neurons express some proteins that inhibit the function of Kat 60 or lack some proteins that promote the functions of Kat 60.They also suggested that Spas and Kat 60,though both are microtubule severing proteins,have distinct cellular functions.Taken together,our findings suggest that the morphology of LNv clock neurons are highly sensitive to the expression levels of microtubule regulatory proteins,making them a suitable cell model for studying the functions of microtubuleassociated proteins;we also show that LNv neurons utilize Spas but not Kat 60 to severing microtubules.Our work thus established a model system to study the principles of how different cell types choose distinct microtubule regulatory proteins to achieve their diverse functions. |
