Defects in Exosome Biogenesis Are Associated with Sensorimotor Defects in Zebrafish vps4a Mutants.

Area of Science:

• Neuroscience
• Cell Biology
• Genetics

Background:

• Mutations in human Vacuolar Protein Sorting 4A (VPS4A) are linked to neurodevelopmental issues, including motor delays and hypotonia.
• VPS4A is a AAA-ATPase crucial for membrane scission, but its role in motor control deficits remains unclear.

Purpose of the Study:

• To investigate how VPS4A mutations affect sensorimotor transformation and motor function using a zebrafish model.
• To elucidate the cellular and molecular mechanisms underlying VPS4A-associated neurodevelopmental defects.

Main Methods:

• Generated and analyzed a zebrafish mutant (vps4a T248I) with reduced Vps4a ATPase activity.
• Assessed sensorimotor reflexes, including optomotor, vestibulospinal, and acoustic startle responses.
• Utilized electroretinography (ERG) and in vivo calcium imaging to evaluate neural pathway function.
• Examined endosomal compartments and exosome levels in mutant larvae.

Main Results:

• The vps4a T248I mutation impaired sensorimotor transformation, leading to absent or severely reduced motor reflexes.
• Mutant larvae exhibited enlarged endosomal compartments and decreased circulating exosomes, consistent with impaired Vps4a function.
• Deficits were observed in retinal function and auditory afferent neuron activity, impacting sensory processing.
• Central pathways showed reduced activation of motor command neurons in response to sensory cues.

Conclusions:

• Defects in sensorimotor transformation, driven by impaired membrane scission and exosome biogenesis due to Vps4a dysfunction, underlie selective motor reflex impairments.
• This study provides insights into the mechanisms of VPS4A-related neurodevelopmental disorders and highlights the importance of Vps4a in neural circuit function.