Identification of a novel mutant allele of LIM homeobox transcription factor 1 alpha (dreher) in mice

A male mouse exhibiting bidirectional circling behavior was identified in a Y-chromosome consomic strain known as DH-Chr Y^RR. The putative mutation responsible for the circling behavior was inherited in an autosomal recessive manner and was termed circ. To identify its causative gene, we performed exome sequencing; of the 34 candidates discovered, we found a novel nonsynonymous single nucleotide variation in LIM homeobox transcription factor 1 alpha (Lmx1a) (c.394G > C, p.Gly132Arg). The genetic linkage between Lmx1a and circ was confirmed in (♀BALB/cA × ♂DH-Chr Y^RR-circ/circ) F₂ and (♀C57BL/6J × ♂DH-Chr Y^RR-circ/circ) F₂ mice. The Lmx1a mutation led to many abnormalities that affected growth, pigmentation, reproduction, and cerebellar morphology. We showed that (♀BALB/cA × ♂DH-Chr Y^RR-circ/circ) F₂-circ/circ mice demonstrated significantly lower body mass than the F₂-+/? mice. Unlike the F₂-+/? mice, few (♀C57BL/6J × ♂DH-Chr Y^RR-circ/circ) F₂-circ/circ mice exhibited a belly spot. The circ/circ females were also invariably sterile, probably because of an underdeveloped uterus. Moreover, the circ/circ mice presented fewer cerebellar granule cells with lower density than the F₂-+/? mice. Although non-complementation between circ and the known Lmx1a mutant alleles remains unconfirmed, the coisogenic nature of circ strongly suggests that it is a novel variant of Lmx1a, previously known as dreher. Therefore, we have assigned the gene symbol Lmx1a^dr-circ to circ. In addition to Lmx1a^dr-J and Lmx1a^dr-kjmi, Lmx1a^dr-circ is the third allele that causes a missense mutation within LIM domains. Identification of missense mutations is necessary to specify the critical residues for abrogating the in vivo functions of LMX1A.