The candidate splicing factor Sfswap regulates growth and patterning of inner ear sensory organs.

The Notch signaling pathway is thought to regulate multiple stages of inner ear development. Mutations in the Notch signaling pathway cause disruptions in the number and arrangement of hair cells and supporting cells in sensory regions of the ear. In this study we identify an insertional mutation in the mouse Sfswap gene, a putative splicing factor, that results in mice with vestibular and cochlear defects that are consistent with disrupted Notch signaling. Homozygous Sfswap mutants display hyperactivity and circling behavior consistent with vestibular defects, and significantly impaired hearing. The cochlea of newborn Sfswap mutant mice shows a significant reduction in outer hair cells and supporting cells and ectopic inner hair cells. This phenotype most closely resembles that seen in hypomorphic alleles of the Notch ligand Jagged1 (Jag1). We show that Jag1; Sfswap compound mutants have inner ear defects that are more severe than expected from simple additive effects of the single mutants, indicating a genetic interaction between Sfswap and Jag1. In addition, expression of genes involved in Notch signaling in the inner ear are reduced in Sfswap mutants. There is increased interest in how splicing affects inner ear development and function. Our work is one of the first studies to suggest that a putative splicing factor has specific effects on Notch signaling pathway members and inner ear development.

ADIPOR1 Is Mutated in Syndromic Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is a genetically heterogeneous retinal disorder. Despite the numerous genes associated with RP already identified, the genetic basis remains unknown in a substantial number of patients and families. In this study, we performed whole-exome sequencing to investigate the molecular basis of a syndromic RP case that cannot be solved by mutations in known disease-causing genes. After applying a series of variant filtering strategies, we identified an apparently homozygous frameshift mutation, c.31delC (p.Q11Rfs*24) in the ADIPOR1 gene. The reported phenotypes of Adipor1-null mice contain retinal dystrophy, obesity, and behavioral abnormalities, which highly mimic those in the syndromic RP patient. We further confirmed ADIPOR1 retina expression by immunohistochemistry. Our results established ADIPOR1 as a novel disease-causing gene for syndromic RP and highlight the importance of fatty acid transport in the retina.

Histone posttranslational modifications and cell fate determination: lens induction requires the lysine acetyltransferases CBP and p300.

Lens induction is a classical embryologic model to study cell fate determination. It has been proposed earlier that specific changes in core histone modifications accompany the process of cell fate specification and determination. The lysine acetyltransferases CBP and p300 function as principal enzymes that modify core histones to facilitate specific gene expression. Herein, we performed conditional inactivation of both CBP and p300 in the ectodermal cells that give rise to the lens placode. Inactivation of both CBP and p300 resulted in the dramatic discontinuation of all aspects of lens specification and organogenesis, resulting in aphakia. The CBP/p300(-/-) ectodermal cells are viable and not prone to apoptosis. These cells showed reduced expression of Six3 and Sox2, while expression of Pax6 was not upregulated, indicating discontinuation of lens induction. Consequently, expression of αB- and αA-crystallins was not initiated. Mutant ectoderm exhibited markedly reduced levels of histone H3 K18 and K27 acetylation, subtly increased H3 K27me3 and unaltered overall levels of H3 K9ac and H3 K4me3. Our data demonstrate that CBP and p300 are required to establish lens cell-type identity during lens induction, and suggest that posttranslational histone modifications are integral to normal cell fate determination in the mammalian lens.

Intracorneal positioning of the lens in Pax6-GAL4/VP16 transgenic mice.

PURPOSE: The purpose of this study was to establish a GAL4/VP16-based binary transactivation system that was active in the lens and corneal epithelium of transgenic mice. METHODS: We generated transgenic mice with the transcriptional transactivator GAL4/VP16 driven by a modified Pax6 promoter that is active in lens and corneal epithelial cells. We also generated and tested UAS-lacZ reporter mice. Wild type and transgenic mice were analyzed by histological, in situ, and Southern hybridization techniques. RESULTS: Five families (OVE1931, OVE1934, OVE1935, OVE1936, and OVE1937) that carry the Pax6-GAL4/VP16 transgene were generated. Unexpectedly, mice from three of the transgenic lines showed ocular abnormalities. In the family OVE1936, cataracts were seen in the heterozygous mice at the time of eyelid opening and homozygotes showed microphthalmia. Transgenic mice in families OVE1931 and OVE1937 appeared normal. Histological analysis of ocular sections of OVE1934, OVE1935, and OVE1936 homozygous transgenic mice showed intracorneal positioning of the lens. The corneal stromal cells were disorganized and there was no distinctive corneal endothelial layer. In situ hybridizations showed robust expression of the GALVP16 transgene in the lens and corneal epithelial cells of the OVE1934, OVE1935, and OVE1936, but not in OVE1931 or OVE1937 families. Bigenic embryos generated by mating the Pax6-GAL4/VP16 mice to the UAS-lacZ mice showed that the GAL4/VP16 transgenic protein is functional and can induce eye-specific expression of a UAS-lacZ reporter gene. CONCLUSIONS: Our data suggest that (1) expression the GAL4/VP16 transgene induces changes in gene expression in lens cells, (2) that developmentally important genes are affected, and (3) that bigenic phenotypes will need to be interpreted with caution.

Insertional mutagenesis by a hybrid piggyBac and sleeping beauty transposon in the rat.

A hybrid piggyBac/Sleeping Beauty transposon-based insertional mutagenesis system that can be mobilized by simple breeding was established in the rat. These transposons were engineered to include gene trap sequences and a tyrosinase (Tyr) pigmentation reporter to rescue the albinism of the genetic background used in the mutagenesis strategy. Single-copy transposon insertions were transposed into the rat genome by co-injection of plasmids carrying the transposon and RNA encoding piggyBac transposase into zygotes. The levels of transgenic Tyr expression were influenced by chromosomal context, leading to transgenic rats with different pigmentation that enabled visual genotyping. Transgenic rats designed to ubiquitously express either piggyBac or Sleeping Beauty transposase were generated by standard zygote injection also on an albino background. Bigenic rats carrying single-copy transposons at known loci and transposase transgenes exhibited coat color mosaicism, indicating somatic transposition. PiggyBac or Sleeping Beauty transposase bigenic rats bred with wild-type albino rats yielded offspring with pigmentation distinct from the initial transposon insertions as a consequence of germline transposition to new loci. The germline transposition frequency for Sleeping Beauty and piggyBac was ∼10% or about one new insertion per litter. Approximately 50% of the insertions occurred in introns. Chimeric transcripts containing endogenous and gene trap sequences were identified in Gabrb1 mutant rats. This mutagenesis system based on simple crosses and visual genotyping can be used to generate a collection of single-gene mutations in the rat.