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Mutations in the SNX14 gene cause spinocerebellar ataxia, autosomal recessive 20 (SCAR20) in both humans and dogs. Studies implicating the phenotypic consequences of SNX14 mutations to be consequences of subcellular disruption to autophagy and lipid metabolism have been limited to in vitro investigation of patient-derived dermal fibroblasts, laboratory engineered cell lines and developmental analysis of zebrafish morphants. SNX14 homologues Snz (Drosophila) and Mdm1 (yeast) have also been conducted, demonstrated an important biochemical role during lipid biogenesis. In this study we report the effect of loss of SNX14 in mice, which resulted in embryonic lethality around mid-gestation due to placental pathology that involves severe disruption to syncytiotrophoblast cell differentiation. In contrast to other vertebrates, zebrafish carrying a homozygous, maternal zygotic snx14 genetic loss-of-function mutation were both viable and anatomically normal. Whilst no obvious behavioural effects were observed, elevated levels of neutral lipids and phospholipids resemble previously reported effects on lipid homeostasis in other species. The biochemical role of SNX14 therefore appears largely conserved through evolution while the consequences of loss of function varies between species. Mouse and zebrafish models therefore provide valuable insights into the functional importance of SNX14 with distinct opportunities for investigating its cellular and metabolic function in vivo. [ABSTRACT FROM AUTHOR]

Severe cases of congenital melanocytic naevi (CMN) are associated with substantial cutaneous and neurological morbidity and an excess childhood mortality from melanoma. Effective treatments are lacking. This mosaic disorder is caused most commonly by a heterozygous oncogenic variant NRAS c.181C>A, p.(Q61K). As NRAS has multiple downstream effectors we have sought to treat this disease by precision genetic therapy rather than downstream pathway inhibition, hypothesising that silencing of the oncogenic allele may remove cellular protection from RAS induced apoptosis. Using a lead siRNA selected for allele specificity and fewest off-target effects on RNAseq (siNRASQ61K) we show here significant selective knockdown of variant mRNA expression and knockdown of NRAS protein levels. A single treatment to primary naevus cell cultures leads to normalisation of MAPK pathway activation, reduction in proliferation rate, and importantly, triggering of apoptosis. We go on to demonstrate that receptor-targeted lipid nanoparticles (RTNPs) successfully protect siRNA from degradation, deliver cargo to naevus cells in patient skin explants and improve naevus cell targeting. A single intradermal injection of siNRASQ61K-RTNPs into transgenic mice harbouring humanised NRASQ61K(Tyr::NRASQ61K) confirms significant selective knockdown of the variant NRAS allele in vivo.Successful targeting of variant NRAS and triggering of naevus cell apoptosis now paves the way for clinical trials of this genetic therapy for CMN. [ABSTRACT FROM AUTHOR]