Molecular definition of an allelic series of mutations disrupting the mouse Lmx1a (dreher) gene Victor Chizhikov, 1 * Ekaterina Steshina, 2 * Richard Roberts, 1 Yesim Ilkin, 1 Linda Washburn, 3 Kathleen J. Millen 1 1 Department of Human Genetics, University of Chicago, 920 E. 58th Street, CLSC 319, Chicago, Illinois 60637, USA 2 Department of Biological Sciences, University of Illinois at Chicago, 900 S. Ashland Avenue, MBRB 4210, Chicago, Illinois 60607, USA 3 The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609, USA Received: 7 March 2006 / Accepted: 20 June 2006 Abstract Mice homozygous for the dreher (dr) mutation are characterized by pigmentation and skeletal abnor- malities and striking behavioral phenotypes, including ataxia, vestibular deficits, and hyperac- tivity. The ataxia is associated with a cerebellar malformation that is remarkably similar to human Dandy-Walker malformation. Previously, positional cloning identified mutations in LIM homeobox transcription factor 1 alpha gene (Lmx1a) in three dr alleles. Two of these alleles, however, are extinct and unavailable for further analysis. In this article we report a new spontaneous dr allele and describe the Lmx1a mutations in this and six additional dr alleles. Strikingly, deletion null, missense, and frameshift mutations in these alleles all cause sim- ilar cerebellar malformations, suggesting that all dr mutations analyzed to date are null alleles. Introduction Mice homozygous for mutations at the dreher (dr) locus are characterized by a complex phenotype that includes circling behavior, balance abnormalities, hyperactivity, deafness, sterility, and pigmentation and tail abnormalities (Lyon 1961; Sweet and Wa- hlsten 1983; Washburn and Eicher 1986). The ataxia demonstrated by dr mutants is caused by a distinct phenotype of cerebellar hypoplasia and abnormal foliation preferentially affecting the cerebellar ver- mis. Interestingly, cerebellar abnormalities in dr/dr mice are very similar to those observed in patients with Dandy-Walker malformation (reviewed in Parisi and Dobyns 2003), suggesting that dreher mice represent a model for this common human birth defect. Other internal abnormalities in homozygous dr mice include neocortical, hippocampal, and spinal cord defects as well as skeletal defects and hypo- plasia of Mullerian duct derivatives (Manzanares et al. 2000; Sekiguchi et al. 1992, 1994; Washburn and Eicher 1986), making dreher mice an excellent model to study neural, skeletal, and reproductive development. Ten spontaneous dr mutant alleles have been described to date. The first dr allele was discovered in four abnormal mice captured in a factory in Det- mold, Germany (Falconer and Sierth-Roth 1951). Subsequently, nine additional dr alleles have been identified (reviewed in Bergstrom et al. 1999). It is unknown if all dr alleles engender the same abnor- mal phenotype or if some phenotypic abnormalities are unique to specific dr alleles. Using a positional cloning strategy, Lmx1a was identified as the dr gene (Millonig et al. 2000). The protein product of Lmx1a has two LIM domains and one homeodomain and belongs to a family of LIM- homeodomain transcription factors (Hobert and Westphal 2000; Hunter and Rhodes 2005). To date, Lmx1a mutations have been described in three dr alleles: dr sst , dr 3J , and dr J . Both dr sst and dr 3J alleles inactivate the Lmx1a gene by deletions that remove the 5¢ portion of the gene, including the ATG translation initiation codon (Millonig et al. 2000). Both dr sst and dr 3J are extinct and not available for further analysis. Currently, dr J is the only molecu- larly defined allele available and mutant mice with this allele have been used extensively in embryo- *These authors contributed equally to this work. Correspondence to: Kathleen J. Millen; E-mail: kmillen@genet- ics.bsd.uchicago.edu DOI: 10.1007/s00335-006-0033-7  Volume 17, 10251032 (2006)  Ó Springer Science+Business Media, Inc. 2006 1025