Role of Usp9X in the Regulation of Axon Specification and Growth

Abstract

Neurons are the core functional cells of the central nervous system (CNS). They are highly polarized with an axon and multiple dendrites, which are critical for the directional transfer of information in the CNS. The axon is the specialised region of the neuron which propagates the signal and forms neural circuits. Improper axon formation and migration can lead to various neurocognitive diseases such as epilepsy and X-linked intellectual disability. Axon formation occurs over three main phases: axon specification, growth and maturation. Axon specification and elongation have been linked to a range of neuronal signalling pathways, kinases and polarity proteins, which are the main regulators of microtubule and actin dynamics. Several studies have shown that the substrate-specific de-ubiquitylating enzyme, Ubiquitin-specific protease located on the X chromosome (Usp9X) plays important roles in the formation and growth of neurons. Three pathological variants of Usp9X, which associate with X-linked intellectual disability, disrupt axonal growth and migration. To examine the role of Usp9X in axon formation and identify the molecular mechanism involved, cultured hippocampal neurons isolated from a brain-specific Usp9X conditional knockout mouse were used. The hippocampi were dissected out at embryonic day 18.5 and neurons were cultured up to 5 days to address the aims of the present studies.