B6.Cg-Pax3^Sp Hoxc13^N/J

Stock number: 000311
Research areas: Cancer Research, Cell Biology Research, Dermatology Research, Developmental Biology Research, Mouse/Human Gene Homologs, Neurobiology Research

Description

Naked (Hoxc13^N) heterozygotes provide a viable model for ectodermal dysplasia 9 (ECTD9) and splotch mutants (Pax3^Sp) provide a model for neural tube developmental defects and Waardenburg syndrome type 1.

Detailed description

This strain carries both the splotch (Pax3^Sp) and naked (Hoxc13^N) spontaneous mutations, which are on Chromosomes 1 and 15, respectively. Mice homozygous for the splotch mutation die by E14 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 feet and often on the back and tail. There are multiple alleles at this locus including splotch-delayed (Pax3^Sp-d, Stock No. 000565), which is similar to splotch but displays caudal rachischisis only.

HOXC13 is a transcription factor that is essential in the regulation of hair development, particularly the hair cycle, and has been found to be oncogenic in some forms of cancer. Normal expression is high in the upper bulb region of hair follicles for all hair types, is initiated during follicle morphogenesis, and expression persists during anagen. The naked mutation, Hoxc13^N, is a spontaneous C to A transversion that changes the TCG serine at amino acid 298 to a TAG stop codon in exon 2, which crops the C-terminal 31 amino acids, including all of helix 3 from the homeobox domain. Mutant protein is expressed and may result in a dominant negative allele. Histochemistry and in situ hybridization of scalp skin from 2-day-old heterozygotes shows a normal nuclear localization of the mutant HOXC13 protein in hair follicle keratinocytes of the matrix and medulla, but homozygotes have a more diffuse labelling in these cells. Homozygotes die between 1 and 14 days of age and on the FVB/N background death is on average slightly earlier than on the C57BL/6J background. Pronounced runting is evident by 4 days of age, the nails are abnormal, vibrissae are absent from birth and there is complete alopecia with the hair breaking just above the skin surface. Hair follicles are smaller than normal, the hair shaft displays coiling and twisting within the infundibulum at 5 days of age, and defects of the hair shaft include poorly keratinized Huxley’s layer and diminution or absences of the cuticle of the inner root sheath. While null alleles of Hoxc13 cause similar alopecia, nail defects and premature death in homozygotes, null heterozygotes have a less severe phenotype than naked heterozygotes. HoxC13^N/+ have a normal lifespan and fertility and look similar to their wildtype littermates for the first week of life, but when the first coat comes in significant alopecia presents, first on the head and anterior trunk with caudal progression on both dorsal and ventral skin then regrowth occurs. In the heterozygote the nails, vibrissae, and other sensory hairs are normal and the hair in the feet, tail and genital area is also normal. Both homozygotes and heterozygotes show changes in the timing of the standard hair cycle and heterozygotes have a mild acceleration of anagen development in response to TPA and a mild acceleration of the transition of keratinocytes through the epidermis in response to BrdU. The severity of this phenotype is impacted by genetic background and heterozygotes provide a viable model for the loss of function alleles that underpin human hair/nail type ectodermal dysplasia 9 (ECTD9).

Development

In 1947 Dr. Elizabeth Russell reported the splotch mutation (Pax3^Sp) spontaneously arising in “the C57 black strain at The Jackson Laboratory”. Dr. George Snell maintained a stock carrying splotch and caracul (Krt71^Ca) in at least the early 1950s. The naked mutation (Hoxc13^N) was first reported in 1927 by N. G. Lebedinsky and A. Dauvart at the University of Latvia in Riga where it was found in a female of an albino stock. It was used by George Snell at The Jackson Laboratory in a mapping cross as early as 1945, and likely imported again in 1950, after the 1947 Bar Harbor fire, from D. Falconer in Edinburgh. Snell maintained a stock that carried a^t, Hoxc13^N, Mitf^mi-wh and T and from this stock an a^t Hoxc13^N T female was bred to a male carrying Krt71^Ca and Pax3^Sp. Their offspring were sibling intercrossed for four generations before a mouse carrying only Hoxc13^N and Pax3^Sp was backcrossed to C57BL/6J for two generations, then the resulting line was maintained by sibling intercrossing for 48 generations before being further backcrossed by Priscilla Lane to her subline of C57BL/6J. In 1982 embryos were generated for cryopreservation from this congenic by breeding a C57BL/6J female to a male heterozygous for both Hoxc13^N and Pax3^Sp at backcross generation N11.

Allele

Symbol: Pax3^Sp
Name: splotch
MGI accession ID: MGI:1856173
Generation method: Spontaneous
Marker symbol: Pax3
Marker name: paired box 3
Chromosome: 1
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.