Gene Mutation Leads to Handstanding Rabbits
What if Bugs Bunny could only move around by doing handstands?
Movement is a necessary function for survival, and different species move in different ways. There are two main types of movement: bipedal (i.e., humans)—walking on two legs or quadrupedal—walking on all four (like a cat).
The coordination between limbs (i.e., right and left legs or all four legs) is controlled by the central pattern generator (CPG) neural networks in the spinal cord.
The Sauteur D'Alfort Rabbit
The Sauteur D'Alfort Rabbit is a particular strain of rabbit that does not jump to walk around; instead, it lifts its hindlimbs to create handstands and walk on front legs. Sauteur D'Alfort Rabbits are also blind.
Image is courtesy of Samuel Boucher.
The Sauter D'Alfort Rabbits differ from other rabbits due to the autosomal recessive allele. Researchers have investigated this rabbit and found interesting conclusions.
The Cameiro et Al (2021) Study on The Sauteur D'Alfort Rabbit
What Did the Researchers Do?
Researchers investigated the genetic basis behind the handstand movement of sauteur rabbits. To do this, they bred male sauter rabbits (with sauter allele) with female white rabbits (without sauter allele; also, they were wildtype that had normal function and movement).
They extracted DNA and sequenced it to find the nucleotide sequence for the whole genome. A genome is an entire set of DNA that makes an organism. After, they looked for regions with higher amounts of genes being expressed (transcribed). Once they found regions with different expression patterns compared to wildtype, they looked for different types of mutations within the area.
The scientists examined the amount of expression and which transcripts were being made the most in the cells using Nanopore technology and explored how the abnormal gene expression affected the neurons in the spinal cord using immunohistochemistry (see below for explanation).
What Did the Researchers Find?
One region on chromosome 1 showed high amounts of abnormal expression in Sauteur rabbits compared to wildtype: this region contained 21 protein-coding genes.
The scientists looked for single nucleotide changes and structural chromosomal changes (i.e., inversions, large insertions/deletions), and found 69 possible mutations in the chromosome 1 region. Only one of the mutations was specific to the Sauteur rabbit (not found in other types of rabbits, and one other mutation was a splice mutation of the RORB gene.
Splice mutation occurred in a conserved region (remains the same sequence) among 70 eutherian mammals (mammals with a placenta). A splice mutation is one that affects how an mRNA transcript is cut to remove introns after being transcribed from DNA.
The gene affected was the RORB gene which codes for the NR1 subfamily of hormone receptors in the cell nucleus. It has been previously shown that mice without RORB protein have a ‘duck-like motor impairment and suffer from retinal degeneration.
Scientists also found that Sauter rabbits do not have average amounts of RORB mRNA; instead, they have high amounts of incomplete transcripts, possibly due to mutation that could cause incorrect cuts of mRNA. Using immunohistochemistry, they found that the incomplete transcripts resulted in fewer spinal cord neurons containing RORB protein which may affect the proper functioning of motor neurons in the spinal cord (leading to motor impairments).
RORB is also known to affect neuronal differentiation, which is what type of neuron a new neuron will become. Scientists found high amounts of interneurons in the spinal cord of the rabbit. Neurons also had abnormal levels of proteins necessary for locomotion (SATB2 and DMRT3). These two cases show that RORB plays a role in neuronal differentiation and that disrupting its function leads to abnormal neurons.
Implications and Future Research
Studies provide some possible links between the Sauteur genotype and its handstand motion and give possible answers for the genes that control locomotion in all animals.
Future research involves exploring what else the mutation could be affecting (e.g., how is RORB affected in the brain) in the body.
Article Authors: Vanessa Wong, Olivia Ye
Article Editor: Stephanie Sahadeo