title: Expression of truncated PITX3 in the developing lens leads to microphthalmia and aphakia in mice.
abstract: Microphthalmia is a severe ocular disorder, and this condition is typically caused by mutations in transcription factors that are involved in eye development. Mice carrying mutations in these transcription factors would be useful tools for defining the mechanisms underlying developmental eye disorders. We discovered a new spontaneous recessive microphthalmos mouse mutant in the Japanese wild-derived inbred strain KOR1/Stm. The homozygous mutant mice were histologically characterized as microphthalmic by the absence of crystallin in the lens, a condition referred to as aphakia. By positional cloning, we identified the nonsense mutation c.444C>A outside the genomic region that encodes the homeodomain of the paired-like homeodomain transcription factor 3 gene (Pitx3) as the mutation responsible for the microphthalmia and aphakia. We examined Pitx3 mRNA expression of mutant mice during embryonic stages using RT-PCR and found that the expression levels are higher than in wild-type mice. Pitx3 over-expression in the lens during developmental stages was also confirmed at the protein level in the microphthalmos mutants via immunohistochemical analyses. Although lens fiber differentiation was not observed in the mutants, strong PITX3 protein signals were observed in the lens vesicles of the mutant lens. Thus, we speculated that abnormal PITX3, which lacks the C-terminus (including the OAR domain) as a result of the nonsense mutation, is expressed in mutant lenses. We showed that the expression of the downstream genes Foxe3, Prox1, and Mip was altered because of the Pitx3 mutation, with large reductions in the lens vesicles in the mutants. Similar profiles were observed by immunohistochemical analysis of these proteins. The expression profiles of crystallins were also altered in the mutants. Therefore, we speculated that the microphthalmos/aphakia in this mutant is caused by the expression of truncated PITX3, resulting in the abnormal expression of downstream targets and lens fiber proteins.
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan; Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Wada
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Research Institute for Clinical Oncology, Saitama Cancer Center, Saitama, Japan.
authors.forename: Yoshibumi
authors.initials: Y
authors.lastname: Matsushima
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Tada
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Hasegawa
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Yo
authors.initials: Y
authors.lastname: Obara
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Yoshizawa
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan.
authors.forename: Gou
authors.initials: G
authors.lastname: Takahashi
authors.affiliation: Medical Innovation Center, Graduate School of Medicine Kyoto University, Kyoto, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hiai
authors.affiliation: Basic Research Center, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Shimanuki
authors.affiliation: Department of Bioproduction, Tokyo University of Agriculture, Abashiri, Japan; Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Sari
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Saitou
authors.affiliation: Institute of Joint Research, Fujita Health University, Toyoake, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamamoto
authors.affiliation: Basic Research Center, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Masumi
authors.initials: M
authors.lastname: Ichikawa
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Mammalian Genetics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kikkawa
mesh_terms: D000818:Animals; D001035:Aphakia / Q000235:genetics* / Q000378:metabolism; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism; D018389:Codon, Nonsense; D003459:Crystallins / Q000235:genetics / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007908:Lens, Crystalline / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008850:Microphthalmos / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D000098551:Prospero-Related Homeobox 1 Protein
chemical_list: D020346:Aquaporins; D018389:Codon, Nonsense; D003459:Crystallins; D005136:Eye Proteins; D051858:Forkhead Transcription Factors; C498612:Foxe3 protein, mouse; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C030328:aquaporin 0; C433629:homeobox protein PITX3; D000098551:Prospero-Related Homeobox 1 Protein