Mice homozygous for the splotch spontaneous mutation (Pax3Sp) die at E13 due to neural tube defects. Malformations of homozygous mutant embryos include rachischisis in the lumbosacral region and frequently in the region of the hindbrain. Heterozygous splotch mice show white spotting on the belly and occasionally on the back, feet, and tail. Splotch is a point mutation within intron 3 of the paired homeobox 3 (Pax3) gene on mouse Chromosome 1. The mutation interferes with normal splicing of intron 3 and leads to at least 4 aberrantly spliced mRNAs with exon 4 deleted. The Pax3Sp mutation also impairs homodimerization of the protein, a function associated with the octapeptide-encoding central segment of the gene. There are multiple alleles at this locus including splotch-delayed (Pax3Sp-d, Stock No. 000565), which is similar to splotch but displays caudal rachischisis only.
|Gene Symbol and Name||Pax3, paired box 3|
|Strain of Origin||C57BL|
|Molecular Note||The mutation comprises the replacement of TCTCCA with CGTGT at the 3' end of intron 3. Since the CA dinucleotide at the end is part of the exon 4 CAG splice acceptor site, this splice site is eliminated in this allele, having been changed to GTG. This mutation abrogates the normal splicing of intron 3, resulting in the generation of four aberrantly spliced mRNA transcripts. Two of these Pax-3 transcripts make use of cryptic 3' splice sites within the downstream exon, generating small deletions which disrupt the reading frame of the transcripts. A third aberrant splicing event results in the deletion of exon 4, while a fourth retains intron 3. These aberrantly spliced mRNA transcripts are not expected to result in functional Pax3 proteins.|