Two zebrafish cacna1s loss-of-function variants provide models of mild and severe CACNA1S-related myopathy.

CACNA1S-related myopathy, due to pathogenic variants in the CACNA1S gene, is a recently described congenital muscle disease. Disease associated variants result in loss of gene expression and/or reduction of Cav1.1 protein stability. There is an incomplete understanding of the underlying disease pathomechanisms and no effective therapies are currently available. A barrier to the study of this myopathy is the lack of a suitable animal model that phenocopies key aspects of the disease. To address this barrier, we generated knockouts of the two zebrafish CACNA1S paralogs, cacna1sa and cacna1sb. Double knockout fish exhibit severe weakness and early death, and are characterized by the absence of Cav1.1 α1 subunit expression, abnormal triad structure, and impaired excitation-contraction coupling, thus mirroring the severe form of human CACNA1S-related myopathy. A double mutant (cacna1sa homozygous, cacna1sb heterozygote) exhibits normal development, but displays reduced body size, abnormal facial structure, and cores on muscle pathologic examination, thus phenocopying the mild form of human CACNA1S-related myopathy. In summary, we generated and characterized the first cacna1s zebrafish loss-of-function mutants, and show them to be faithful models of severe and mild forms of human CACNA1S-related myopathy suitable for future mechanistic studies and therapy development.

Resolving primary pathomechanisms driving idiopathic-like spinal curvature using a new katnb1 scoliosis model.

Idiopathic scoliosis (IS) refers to abnormal spinal curvatures that occur in the absence of vertebral or neuromuscular defects. IS accounts for 80% of human spinal deformity, afflicts ∼3% of children worldwide, yet pathogenic mechanisms are poorly understood. A key role for cerebrospinal fluid (CSF) homeostasis in zebrafish spine development has been identified. Specifically, defects in cilia motility of brain ependymal cells (EC), CSF flow, and/or Reissner fiber (RF) assembly are observed to induce neuroinflammation, oxidative stress, abnormal CSF-contacting neuron activity, and urotensin peptide expression, all associating with scoliosis. However, the functional relevance of these observations to IS remains unclear. Here we characterize zebrafish katnb1 mutants as a new IS model. We define essential roles for Katnb1 in motile ciliated lineages, uncouple EC cilia and RF formation defects from spinal curvature, and identify abnormal CSF flow and cell stress responses as shared pathogenic signatures associated with scoliosis across diverse zebrafish models.

SCO-Spondin Defects and Neuroinflammation Are Conserved Mechanisms Driving Spinal Deformity across Genetic Models of Idiopathic Scoliosis.

Adolescent idiopathic scoliosis (AIS) affects 3% to 4% of children between the ages of 11 and 18 [1, 2]. This disorder, characterized by abnormal three-dimensional spinal curvatures that typically develop during periods of rapid growth, occurs in the absence of congenital vertebral malformations or neuromuscular defects [1]. Genetic heterogeneity [3] and a historical lack of appropriate animal models [4] have confounded basic understanding of AIS biology; thus, treatment options remain limited [5, 6]. Recently, genetic studies using zebrafish have linked idiopathic-like scoliosis to irregularities in motile cilia-mediated cerebrospinal fluid flow [7-9]. However, because loss of cilia motility in human primary ciliary dyskinesia patients is not fully associated with scoliosis [10, 11], other pathogenic mechanisms remain to be determined. Here, we demonstrate that zebrafish scospondin (sspo) mutants develop late-onset idiopathic-like spinal curvatures in the absence of obvious cilia motility defects. Sspo is a large secreted glycoprotein functionally associated with the subcommissural organ and Reissner's fiber [12]-ancient and enigmatic organs of the brain ventricular system reported to govern cerebrospinal fluid homeostasis [13, 14], neurogenesis [12, 15-18], and embryonic morphogenesis [19]. We demonstrate that irregular deposition of Sspo within brain ventricles is associated with idiopathic-like scoliosis across diverse genetic models. Furthermore, Sspo defects are sufficient to induce oxidative stress and neuroinflammatory responses implicated in AIS pathogenesis [9]. Through screening for chemical suppressors of sspo mutant phenotypes, we also identify potent agents capable of blocking severe juvenile spine deformity. Our work thus defines a new preclinical model of AIS and provides tools to realize novel therapeutic strategies.