Characterization of the neb (sa906) mutant zebrafish strain. a & b) At 4 dpf neb^?/? zebrafish (aii) appear smaller in size and (bii) display a loss of birefringence compared to their wildtype siblings (ai & bi). c) RT-PCR analysis in and neb^?/? mutant embryos at 2 dpf shows a reduction in neb mRNA levels compared to wildtype siblings (sibling). ?Act was used as a positive control. d) ii) neb^?/? mutants display a smaller eye, brain region (B) and deflated swim bladder (SB) compared to their i) wildtype siblings. e) Quantification of the maximum acceleration recorded from touch-evoked response assays of neb^?/? fish compared to wildtype siblings at 2 dpf. Error bars represent mean±SEM for three independent experiments (n =?11,9,12 neb ^?/? , 55,25,32 neb ^+/? , 18,13,12 neb ^+/+ zebrafish per experiment), **p <?0.01. f & g) Quantification of the normalized (f) distance and (g) speed travelled by neb^?/? mutants compared to wildtype siblings at 6 dpf. For f) error bars represent median±interquartile range for three independent experiments (for n =?19,23,19 neb ^?/? , 41,42,36 neb ^+/? , 31,20,21 neb ^+/+ zebrafish). For g) error bars represent mean±SEM range (for n?=?19,23,14 neb ^?/? , 41,42,36 neb ^+/? , 30,20,21 neb ^+/+ zebrafish per experiment). *p <?0.5, **** p <?0.001

Characterisation of skeletal muscle pathology in neb^?/? fish. a Gomori trichome staining of neb^?/? skeletal muscle sections reveal the presence of dark regions (arrows) throughout the muscle indicative of nemaline bodies not observed in neb ^+/+ fish. Nuclei (arrowhead) are evenly organized in neb ^+/+ , however, appear disorganized in neb^?/? fish. b Quantification of normalized fiber area from Gomori trichome stained sections in neb^?/? (n?=?23 fibers) compared to neb^+/+ fish (n?=?21 fibers). Error bars represent mean±SD, *** p <?0.001. c neb^?/? mutants exhibit F-actin (red) and Actinin2 (green) positive aggregates at the myosepta (arrowheads) (and zoomed inset) compared to wildtype siblings at 2 dpf

Examination of neb^?/? skeletal muscle by electron microscopy. a) neb ^?/? mutant skeletal muscles display (i, iv) thickened Z-disks (arrows), (ii) fiber breakage (asterisks), (iii) accumulations of nemaline bodies and (iv) disruption of sarcomeric structures that are not observed in b) neb ^+/+ wildtype siblings

Quantification of the phenotypic severity of neb ^?/? mutants at 6 dpf. Quantification of the phenotypic severity of Tg(neb ^?/? ; Lifeact-eGFP) fish at 6 dpf supplemented with either L-tyrosine, taurine, L-carnitine, creatine, or water (H₂O). a Phenotypes were scored as either wildtype, mild (less than five Lifeact-eGFP positive aggregates at the myosepta or a mild disruption of muscle fibres), or severe (severely disorganised fibres or an accumulation of five or more Lifeact-eGFP positive aggregates within the muscle cell). b Quantification of the phenotypic severity of Tg(neb ^?/? ; Lifeact-eGFP) fish supplemented with either L-tyrosine, taurine, or water. c Quantification of the phenotypic severity of Tg(neb ^?/? ; Lifeact-eGFP) fish supplemented with either L-carnitine, creatine, or water (H₂O). b & c Error bars represent mean±SEM for three independent experiments. For b) n =?6,8,7 Tg(neb ^?/? ; Lifeact-eGFP) for L-tyrosine, n?=?11,5,11 Tg(neb ^?/? ; Lifeact-eGFP) for taurine and n?=?9,8,10 Tg(neb ^?/? ; Lifeact-eGFP) for water. For c) n?=?8,10,4 Tg(neb ^?/? ; Lifeact-eGFP) for L-carnitine, n?=?6,8,3 Tg(neb ^?/? ; Lifeact-eGFP) for creatine, and n =?10,9,5 Tg(neb ^?/? ; Lifeact-eGFP) for water per experiment). ns?=?not significant

Characterisation of Tg(neb^-/-; Lifeact-eGFP) fish.

Tg(neb^-/-; Lifeact-eGFP) fish show an accumulation of Lifeact-eGFP at the myosepta (arrowheads) at both 2 dpf and 6 dpf as well as regions of disorxganized muscle fibers (arrows) at 6 dpf that are not observed in Tg(neb^+/+; Lifeact-eGFP) siblings.

Characterisation of facial muscles in Tg(neb^-/-; Lifeact-eGFP) fish and wild type siblings at 6 dpf.

Maximum projection images of Tg(neb^-/-; Lifeact-eGFP) fish supplemented with water, tyrosine, taurine, L-carnitine of creatine show no difference in the appearance of facial muscles to Tg(neb^+/+; Lifeact-eGFP) siblings supplemented with water.