City Research Online

Abstract

Adams-Oliver syndrome (AOS) is a rare developmental disorder, predominantly characterised by scalp and limb anomalies. A wide range of additional clinical features, including neurological, vascular and/or cardiac defects, are observed. Of the six known causal genes, ARHGAP31 and DOCK6 encode Rho GTPase regulators for Cdc42 and Rac1 activity. Nonetheless, the molecular mechanisms underlying Cdc42/Rac1 dysregulation in AOS remain largely unexplored.

AOS is hypothesised to be a disorder of vasculogenesis, therefore I sought to model ARHGAP31 and DOCK6 dysfunction using zebrafish to examine the mechanisms underlying perturbed vascularisation. Normal dock6 and arhgap31 expression during embryogenesis were characterised using quantitative PCR, whole-mount in situ hybridisation and a novel dock6 transgenic line. Vascular development in morpholino- and CRISPR-mediated disease models was quantified using
microangiography and a tg(fli1:EGFP) transgenic zebrafish line. To investigate the cellular mechanisms underpinning vascular defects in AOS, siRNA-mediated DOCK6 knockdown was evaluated in human vascular smooth muscle and epidermal keratinocyte cell lines.

Expression of arhgap31 and dock6 localised to some vascular and neural crest-derived structures throughout embryogenesis. Gene knockdown promoted cardiovascular and neural crest-related defects. Reduced arhgap31 expression impaired enlargement of the brain ventricles and increased Notch signalling, indicating a potential novel overlap between the Rho and Notch pathways in AOS. Both disease models exhibited impaired intersegmental vessel (ISV) and optic vessel sprouting, asymmetric and truncated ISVs. Vessel leakage and limited vessel perfusion implied a critical role for arhgap31 and dock6 during zebrafish vascularisation. In human cell lines, DOCK6 knockdown disrupted cell adhesion and phalloidin staining revealed defective cytoskeletal, lamellipodia and filopodia formation.

Together, this work suggests a model of impaired cell adhesion impeding normal vascular development in AOS, with a potential origin in the neural crest. These novel findings confirm vascular disruption as a key factor in AOS pathogenesis, advancing our understanding of the mechanisms underpinning this debilitating disorder.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QH Natural history > QH301 Biology Q Science > QH Natural history > QH426 Genetics R Medicine
Departments:	School of Health & Medical Sciences > School of Health & Medical Sciences Doctoral Theses Doctoral Theses

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