Novel Dominant and Recessive Variants in Human ROBO1 Cause Distinct Neurodevelopmental Defects Through Different Mechanisms

Authors

Yan Huang
Mengqi Ma
Xiao Mao
Davut Pehlivan
Oguz Kanca
Feride Un-Candan
Li Shu
Gulsen Akay
Tadahiro Mitani
Shenzhao Lu
Sukru Candan
Hua Wang
Bo Xiao
James R Lupski
Hugo J Bellen

Publication Date

8-23-2022

Journal

Human Molecular Genetics

DOI

10.1093/hmg/ddac070

PMID

35348658

PMCID

PMC9402236

PubMedCentral® Posted Date

3-26-2022

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes

Keywords

Animals, Axons, Drosophila, Drosophila Proteins, Humans, Nerve Tissue Proteins, Neurodevelopmental Disorders, Receptors, Immunologic, Roundabout Proteins

Abstract

The Roundabout (Robo) receptors, located on growth cones of neurons, induce axon repulsion in response to the extracellular ligand Slit. The Robo family of proteins controls midline crossing of commissural neurons during development in flies. Mono- and bi-allelic variants in human ROBO1 (HGNC: 10249) have been associated with incomplete penetrance and variable expressivity for a breath of phenotypes, including neurodevelopmental defects such as strabismus, pituitary defects, intellectual impairment, as well as defects in heart and kidney. Here, we report two novel ROBO1 variants associated with very distinct phenotypes. A homozygous missense p.S1522L variant in three affected siblings with nystagmus; and a monoallelic de novo p.D422G variant in a proband who presented with early-onset epileptic encephalopathy. We modeled these variants in Drosophila and first generated a null allele by inserting a CRIMIC T2A-GAL4 in an intron. Flies that lack robo1 exhibit reduced viability but have very severe midline crossing defects in the central nervous system. The fly wild-type cDNA driven by T2A-Gal4 partially rescues both defects. Overexpression of the human reference ROBO1 with T2A-GAL4 is toxic and reduces viability, whereas the recessive p.S1522L variant is less toxic, suggesting that it is a partial loss-of-function allele. In contrast, the dominant variant in fly robo1 (p.D413G) affects protein localization, impairs axonal guidance activity and induces mild phototransduction defects, suggesting that it is a neomorphic allele. In summary, our studies expand the phenotypic spectrum associated with ROBO1 variant alleles.