A loss-of-function mutation in RORB disrupts saltatorial locomotion in rabbits

Abstract

Saltatorial locomotion is a type of hopping gait that in mammals can be found in rabbits, hares, kangaroos, and some species of rodents. The molecular mechanisms that control and fine-tune the formation of this type of gait are unknown. Here, we take advantage of one strain of domesticated rabbits, the sauteur d’Alfort, that exhibits an abnormal locomotion behavior defined by the loss of the typical jumping that characterizes wild-type rabbits. Strikingly, individuals from this strain frequently adopt a bipedal gait using their front legs. Using a combination of experimental crosses and whole genome sequencing, we show that a single locus containing the RAR related orphan receptor B gene (RORB) explains the atypical gait of these rabbits. We found that a splice-site mutation in an evolutionary conserved site of RORB results in several aberrant transcript isoforms incorporating intronic sequence. This mutation leads to a drastic reduction of RORB-positive neurons in the spinal cord, as well as defects in differentiation of populations of spinal cord interneurons. Our results show that RORB function is required for the performance of saltatorial locomotion in rabbits.

An allelic series of spontaneous mutations in Rorb cause a gait phenotype, retinal abnormalities, and transcriptomic changes relevant to human neurodevelopmental conditions

“…We have also demonstrated that, although the number of Rorb-expressing cells in somatosensory cortex is not dramatically different between mutant and WT mice, the expression of Scnn1a is markedly different, with many fewer cells labeled in mutant mice. We therefore support the finding that, in layer 4 neurons, Rorb is important for cell fate and/or terminal differentiation, similar to what has been reported previously regarding cortical barrels, spinal cord, and retina (KAUTZMANN et al 2011;LIU et al 2013b;FU et al 2014;WANG et al 2014;CLARK et al 2020;CARNEIRO et al 2021). Thus, while Rorb-expressing cells are still present in sensory areas in mutant mice, they may not function normally in cortical circuitry.…”

“…was recently shown to underlie abnormal gait in sauteur d'Alfort rabbits (CARNEIRO et al 2021). Delayed onset of fertility in male mice with Rorb mutations has also been described previously (ANDRE et al 1998b).…”

“…In mice, Rorb knockout causes a characteristic gait phenotype referred to as "high stepper" or "duck gait," which was associated with electrophysiological dysfunction in a subpopulation of Pax2+ inhibitory spinal interneurons that require RORB for proper gating of input and rhythmic output from the central pattern generator of the spinal cord (KOCH et al 2017). A mechanism whereby splice-site mutations in RORB cause reduction of RORB-positive neurons in the spinal cord and abnormal spinal interneuron differentiation was recently shown to underlie abnormal gait in sauteur d'Alfort rabbits (CARNEIRO et al 2021). Delayed onset of fertility in male mice with Rorb mutations has also been described previously (ANDRE et al 1998b).…”

Human photoreceptor cells from different macular subregions have distinct transcriptional profiles

“…7A ), with comparable expression between the fovea and parafovea ( Supplementary Material, Table S2 ). Previous studies have shown that retinal RORB expression regulates circadian timing ( 36 ) and is important for neuronal differentiation and patterning ( 37 , 38 ). RORB encodes two isoforms with distinct N-terminal domains.…”

Multiple causal DNA variants in a single gene affect gene expression intrans

“…Efforts to identify the molecular cause of a QTL often implicitly assume that the QTL contains only a single causal variant that can be "fine-mapped" through a series of experiments, aided by annotations of gene function and, more recently, computational predictions of variant effect (Adzhubei et al, 2013;Choi and Chan, 2015;Kircher et al, 2014;Sim et al, 2012). Well-known success stories demonstrate that single causal genes and variants can be identified in QTLs (Carneiro et al, 2021;Sutter et al, 2007;Van Laere et al, 2003).…”