Expression of truncated PITX3 in the developing lens leads to microphthalmia and aphakia in mice.

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.

Transgenic mouse model for the study of enterovirus 71 neuropathogenesis.

Enterovirus 71 (EV71) typically causes mild hand-foot-and-mouth disease in children, but it can also cause severe neurological disease. Recently, epidemic outbreaks of EV71 with significant mortality have been reported in the Asia-Pacific region, and EV71 infection has become a serious public health concern worldwide. However, there is little information available concerning EV71 neuropathogenesis, and no vaccines or anti-EV71 drugs have been developed. Previous studies of this disease have used monkeys and neonatal mice that are susceptible to some EV71 strains as models. The monkey model is problematic for ethical and economical reasons, and mice that are more than a few weeks old lose their susceptibility to EV71. Thus, the development of an appropriate small animal model would greatly contribute to the study of this disease. Mice lack EV71 susceptibility due to the absence of a receptor for this virus. Previously, we identified the human scavenger receptor class B, member 2 (hSCARB2) as a cellular receptor for EV71. In the current study, we generated a transgenic (Tg) mouse expressing hSCARB2 with an expression profile similar to that in humans. Tg mice infected with EV71 exhibited ataxia, paralysis, and death. The most severely affected cells were neurons in the spinal cord, brainstem, cerebellum, hypothalamus, thalamus, and cerebrum. The pathological features in these Tg mice were generally similar to those of EV71 encephalomyelitis in humans and experimentally infected monkeys. These results suggest that this Tg mouse could represent a useful animal model for the study of EV71 infection.

Comprehensive application of an mtDsRed2-Tg mouse strain for mitochondrial imaging.

Mitochondria are essential for many cellular functions such as oxidative phosphorylation and calcium homeostasis; consequently, mitochondrial dysfunction could cause many diseases, including neurological disorders. Recently, mitochondrial dynamics, such as fusion, fission, and transportation, have been visualized in living cells by using time-lapse imaging systems. The changes in mitochondrial morphology could be an indicator for estimating the activity of mitochondrial biological function. Here, we report a transgenic mouse strain, mtDsRed2-Tg, which expresses a red fluorescent protein, DsRed2, exclusively in mitochondria. Mitochondrial morphology could be clearly observed in various tissues of this strain under confocal microscope. Recently, many transgenic mouse strains in which enhanced green fluorescent protein (EGFP)-tagged proteins of interest are expressed have been established for physiological analysis in vivo. After mating these strains with mtDsRed2-Tg mice, red-colored mitochondria and green-colored proteins were detected simultaneously using fluorescent imaging systems, and the interactions between mitochondria and those proteins could be morphologically analyzed in cells and tissues of the F(1) hybrids. Thus, mtDsRed2-Tg mice can be a powerful tool for bioimaging studies on mitochondrial functions.

p62/SQSTM1 cooperates with Parkin for perinuclear clustering of depolarized mitochondria.

PINK1 and Parkin were first identified as the causal genes responsible for familial forms of early-onset Parkinson's disease (PD), a prevalent neurodegenerative disorder. PINK1 encodes a mitochondrial serine/threonine protein kinase, whereas Parkin encodes an ubiquitin-protein ligase. PINK1 and Parkin cooperate to maintain mitochondrial integrity; however, the detailed molecular mechanism of how Parkin-catalyzed ubiquitylation results in mitochondrial integrity remains an enigma. In this study, we show that Parkin-catalyzed K63-linked polyubiquitylation of depolarized mitochondria resulted in ubiquitylated mitochondria being transported along microtubules to cluster in the perinuclear region, which was interfered by pathogenic mutations of Parkin. In addition, p62/SQSTM1 (hereafter referred to as p62) was recruited to depolarized mitochondria after Parkin-directed ubiquitylation. Intriguingly, deletion of p62 in mouse embryonic fibroblasts resulted in a gross loss of mitochondrial perinuclear clustering but did not hinder mitochondrial degradation. Thus, p62 is required for ubiquitylation-dependent clustering of damaged mitochondria, which resembles p62-mediated 'aggresome' formation of misfolded/unfolded proteins after ubiquitylation.

Global imaging of mitochondrial morphology in tissues using transgenic mice expressing mitochondrially targeted enhanced green fluorescent protein.

The most common approach to analyzing the static morphology of mitochondria involves staining by antibodies or fluorescent dyes specific for mitochondrial components. In this study, we present a new approach using transgenic (Tg) mice, mtGFP-Tg mice, which exclusively express EGFP in the mitochondrial matrix. This Tg strain enables the rapid and easy observation of mitochondria in many kinds of tissues of interest. Recently, many reports have indicated that mitochondrial abnormalities and disease phenotypes are closely associated. mtGFP-Tg mice will be very useful in demonstrating this association, via the use of hybrids of mtGFP-Tg mice and well-established model mice for human diseases.