Microtubule-Associated Proteins (MAPs) Are Multifunctional Cytoskeletal Proteins in the Testis That Regulate Spermatogenesis.

Microtubule-associated proteins (MAPs) refer to a large superfamily of proteins that bind to microtubules (MTs) structurally, modulating the rapid transition of MTs from a stable state (polymerized) to shrinkage (or catastrophe) via depolymerization through a meta-stable state. Changes of MTs from an assembled structure as linear protofilaments that are a packed/bundled ultrastructure to disassembled subunits of heterodimers of α-/ß-tubulins (or oligomers) can take place in milliseconds within a living cell. These heterodimers can also be rapidly phosphorylated, becoming GTP-bound, or rapidly polymerized into linear protofilaments of MT again. It is such rapid cyclic changes of MTs that support cellular development, growth, and changes in cell shape in response to changes in development or other physiological phenomena, such as the series of cellular events during spermatogenesis, cell divisions, and in response to environmental toxicants to protect cellular life. In this review, we seek to give a concise update and discussion on MAPs. Particularly, we focus on a specific member of the structural MAPs, namely MAP1a, and its interaction with the microtubule affinity regulatory kinases (MARKs, including MARK1, 2, 3, and 4, all are Ser/Thr protein kinases) in particular MARK4, and how these two MAPs work together to regulate MT dynamics in Sertoli cells to support germ cell development. This information should be helpful to investigators who seek to better understand the role of MAPs in testis biology.