The LIM and SH3 domain protein 1 (LASP1) was originally identified in metastatic breast cancer and mainly characterized as a cytoskeleton protein overexpressed in various cancer types. At present, little is known about LASP1 expression in physiological conditions, and its function during embryonic development has not been elucidated. Here, we focused on Lasp1 and embryonic development, choosing zebrafish as a vertebrate model. For the first time, we identified and determined the expression of Lasp1 protein at various stages of development, at 48 and 72 h post-fertilization (hpf), at 6 days pf and in different organs of zebrafish adults by Western blotting, 3D light-sheet microscopy and fluorescent immunohistochemistry. Further, we showed that specific lasp1 morpholino (MO) led to (i) abnormal morphants with alterations in several organs, (ii) effective knockdown of endogenous Lasp1 protein and (iii) an increase in lasp1 mRNA, as detected by ddPCR. The co-injection of lasp1 mRNA with lasp1 MO partially rescued morphant phenotypes, thus confirming the specificity of the MO oligonucleotide-induced defects. We also detected an increase in apoptosis following lasp1 MO treatment. Our results suggest a significant role for Lasp1 in embryonic development, highlighting zebrafish as a vertebrate model suitable for studying Lasp1 function in developmental biology and organogenesis.

Missense mutations in MYOT encoding the sarcomeric Z‐disk protein myotilin cause three main myopathic phenotypes including proximal limb‐girdle muscular dystrophy, spheroid body myopathy, and late‐onset distal myopathy. We describe a family carrying a heterozygous MYOT deletion (Tyr4_His9del) that clinically was characterized by an early‐adult onset distal muscle weakness and pathologically by a myofibrillar myopathy (MFM). Molecular modeling of the full‐length myotilin protein revealed that the 4‐YERPKH‐9 amino acids are involved in local interactions within the N‐terminal portion of myotilin. Injection of in vitro synthetized mutated human MYOT RNA or of plasmid carrying its cDNA sequence in zebrafish embryos led to muscle defects characterized by sarcomeric disorganization of muscle fibers and widening of the I‐band, and severe motor impairments. We identify MYOT novel Tyr4_His9 deletion as the cause of an early‐onset MFM with a distal myopathy phenotype and provide data supporting the importance of the amino acid sequence for the structural role of myotilin in the sarcomeric organization of myofibers.

Myofibrillar myopathies (MFMs) are a group of hereditary neuromuscular disorders sharing common histological features, such as myofibrillar derangement, Z-disk disintegration, and the accumulation of degradation products into protein aggregates. They are caused by mutations in several genes that encode either structural proteins or molecular chaperones. Nevertheless, the mechanisms by which mutated genes result in protein aggregation are still unknown. To unveil the role of myotilin and αB-crystallin in the pathogenesis of MFM, we injected zebrafish fertilized eggs at the one-cell stage with expression plasmids harboring cDNA sequences of human wildtype or mutated MYOT (p.Ser95Ile) and human wildtype or mutated CRYAB (p.Gly154Ser). We evaluated the effects on fish survival, motor behavior, muscle structure and development. We found that transgenic zebrafish showed morphological defects that were more severe in those overexpressing mutant genes. which developed a myopathic phenotype consistent with that of human myofibrillar myopathy, including the formation of protein aggregates. Results indicate that pathogenic mutations in myotilin and αB-crystallin genes associated with MFM cause a structural and functional impairment of the skeletal muscle in zebrafish, thereby making this non-mammalian organism a powerful model to dissect disease pathogenesis and find possible druggable targets.