title: A 5-bp insertion in Mip causes recessive congenital cataract in KFRS4/Kyo rats.
abstract: We discovered a new cataract mutation, kfrs4, in the Kyoto Fancy Rat Stock (KFRS) background. Within 1 month of birth, all kfrs4/kfrs4 homozygotes developed cataracts, with severe opacity in the nuclei of the lens. In contrast, no opacity was observed in the kfrs4/+ heterozygotes. We continued to observe these rats until they reached 1 year of age and found that cataractogenesis did not occur in kfrs4/+ rats. To define the histological defects in the lenses of kfrs4 rats, sections of the eyes of these rats were prepared. Although the lenses of kfrs4/kfrs4 homozygotes showed severely disorganised fibres and vacuolation, the lenses of kfrs4/+ heterozygotes appeared normal and similar to those of wild-type rats. We used positional cloning to identify the kfrs4 mutation. The mutation was mapped to an approximately 9.7-Mb region on chromosome 7, which contains the Mip gene. This gene is responsible for a dominant form of cataract in humans and mice. Sequence analysis of the mutant-derived Mip gene identified a 5-bp insertion. This insertion is predicted to inactivate the MIP protein, as it produces a frameshift that results in the synthesis of 6 novel amino acid residues and a truncated protein that lacks 136 amino acids in the C-terminal region, and no MIP immunoreactivity was observed in the lens fibre cells of kfrs4/kfrs4 homozygous rats using an antibody that recognises the C- and N-terminus of MIP. In addition, the kfrs4/+ heterozygotes showed reduced expression of Mip mRNA and MIP protein and the kfrs4/kfrs4 homozygotes showed no expression in the lens. These results indicate that the kfrs4 mutation conveys a loss-of-function, which leads to functional inactivation though the degradation of Mip mRNA by an mRNA decay mechanism. Therefore, the kfrs4 rat represents the first characterised rat model with a recessive mutation in the Mip gene.
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Watanabe
authors.forename: Kenta
authors.initials: K
authors.lastname: Wada
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ohashi
authors.forename: Saki
authors.initials: S
authors.lastname: Okubo
authors.forename: Kensuke
authors.initials: K
authors.lastname: Takekuma
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hashizume
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Hayashi
authors.forename: Tadao
authors.initials: T
authors.lastname: Serikawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Kuramoto
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kikkawa
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000737:chemistry / Q000235:genetics*; D002386:Cataract / Q000235:genetics*; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics*; D005786:Gene Expression Regulation; D005808:Genes, Recessive / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats
chemical_list: D020346:Aquaporins; D005136:Eye Proteins; D012333:RNA, Messenger; C030328:aquaporin 0