Impaired larval motor function in a zebrafish Stathmin-2 (STMN2) knockout model

Abstract

Stathmin-2 (STMN2) is a microtubule associated protein that plays a role in the stability of microtubules of axons in the nervous system of animals. In this study we generated a novel zebrafish STMN2 knockout (KO) model. STMN2 is represented by two genes in the zebrafish genome: stmn2a and stmn2b. Using the CRISPR/Cas9 mutagenic system we selected founder fish lines harbouring frameshift mutations in both genes and bred these together to generate a double stmn2a and stmn2b KO model. Using these models, we observed increased developmental lethality in our double stmn2a and stmn2b KO model and impaired motor function at larval stages of development. Examination of the larval neuromuscular junction (NMJ) revealed a slight increase in the number of orphaned NMJs in trunk musculature as well as a reduction in amplitude of miniature endplate currents in our double stmn2a and stmn2b KO model. In a final series of experiments, we show impaired ventral root axon regrowth following transection in double stmn2a and stmn2b KO larvae. Our findings suggest that while not essential for motor axon development, loss of stmn2a and stmn2b expression perturbs the assembly of zebrafish NMJs during development resulting in a minor motor phenotype and impairs that ability to regenerate motor axons following injury.