The role of α-tubulin acetylation in the regulation of murine sperm motility

Abstract

Sperm motility is a vital function required for fertility and is a consequence of interactions between components of the axoneme in the sperm flagellum. Microtubules, made up of α and β-tubulin, are a central component of the axoneme and undergo various post translational modifications. One such modification is the acetylation of the lysine 40 residue of α-tubulin which is carried out by α-tubulin acetyltransferase (α-TAT1), and is deacetylated by the activities of histone deacetylase 6 (HDAC6) and SIRT2. Recently, research has implicated α-tubulin acetylation in the regulation of sperm motility. The work presented in this thesis therefore aimed to study the influence that the state of α-tubulin acetylation has on sperm function by assessing the role of α-tubulin deacetylation in sperm motility modulation. To do this, murine sperm were treated with the HDAC6-specific inhibitor, tubacin; the general Class I and II HDAC inhibitor trichostatin A (TSA); and the general Class III HDAC inhibitor, nicotinamide. Exposure to the inhibitors did not significantly affect sperm motility or levels of acetylated α-tubulin. Furthermore, high baseline levels of acetylated α-tubulin were found in sperm. Subsequent examination of HDAC activity demonstrated that HDAC6 was active and could be inhibited in live murine sperm. Taken together, the results indicated that HDAC6 activity in sperm was low, suggesting that highly acetylated α-tubulin may be important for sperm function. As acetylation is indicative of microtubule stability, the effect of microtubule destabilisation using the drug, nocodazole, was assessed. Both α-tubulin organisation and acetylation remained intact in sperm following treatment, though nocodazole was found to significantly enhance certain motility parameters. This thesis therefore reports the novel finding that treatment with a microtubule depolymerising drug can alter sperm motility, indicating that subtle changes in microtubule conformation may influence flagellar motion which could have important implications for infertility caused by impaired sperm motility.