Homozygous mice are viable and fertile, with the Axin2lacZ (or conductinlacZ) mutation that both abolishes endogenous Axin2 gene function and expresses NLS-lacZ under the control of the endogenous Axin2 promoter/enhancer regions. Homozygous mice exhibit cranial skull defects and malformations of skull structures; a phenotype resembling craniosynostosis in humans. Specifically, homozygous mice show an obvious reduction in head growth within the first 3 weeks after birth, resulting from developmental defects of the cranial skull (premature fusion of cranial sutures) at early postnatal stages. Axin2-deficient mice have abnormal calvarial morphogenesis/osteoblast development. Because Axin2 is a negative regulator of the canonical Wnt pathway that suppress signal transduction by promoting β-catenin degradation, the NLS-lacZ expression in these Axin2lacZ (or conductinlacZ) mutant mice may be useful in monitoring endogenous canonical Wnt signals in many tissues and organs during development, regeneration and tumorigenesis.
C57BL/6N-derived mice are homozygous for the recessive mutation retinal degeneration 8 (Crb1rd8) - identified as a single base deletion in the Crb1 gene that causes a frame shift and premature stop codon that truncates the transmembrane and cytoplasmic domain of the protein.
Mice homozygous for Crb1rd8 exhibit retinal external limiting membrane fragmentation and outer retinal dysplasia, as well as multifocal retinal degeneration and the accumulation of subretinal microglia/macrophages [Mattapallil et al. 2012 Invest Ophthalmol Vis Sci. 53:2921 , Mehalow et al. 2003 Hum Mol Genet. 12:2179 ,
Luhmann et al. 2012 PLoS One 7:e35551]. Of note, C57BL/6J-derived mice are homozygous for the wildtype Crb1 allele.
