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Dominantly acting mutations that produce visible phenotypes are frequently recovered, either during routine maintenance of colonies or from mutagenesis experiments. We have studied 12 dominant mouse mutations that cause a tail dysmorphology, a coat spotting phenotype, or a combination of these. The majority of these mutations act in a semidominant manner with the homozygous state associated with embryonic lethality and a visible phenotype at or before midgestation. The homozygous phenotypes include axis truncation and neural crest cell defects, as may be expected from the heterozygous phenotypes. The majority of mutations, however, also produced other phenotypes that include neural tube closure defects and aberrant heart looping. In one coat spotting mutant the homozygous condition is lethal before neural crest cell production commences. The mutated genes often function in processes additional to those alluded to by the heterozygous phenotype.

Although the gross embryology of inner ear development has been documented for several different vertebrate species at a descriptive level, our understanding of the molecular mechanisms involved remains rudimentary. Therefore, we have used cDNA subtraction and normalization procedures to define genes upregulated in the 13.5dpc mouse inner ear, a developmental stage where inner ear morphogenesis and tissue remodeling is active and differentiation of future hair cells is being initiated. We recovered 33 different genes from this subtraction and using gene-specific primers have confirmed the transcriptional upregulation of 26 of these in the 13.5dpc inner ear. Northern analyses were used to investigate splicing differences between the inner ear and the whole embryo at 13.5dpc. Spatial localization of expression was determined through whole-ear in situ hybridization analysis, and selected genes were analyzed in more detail through in situ hybridization of tissue sections. These data illustrate that the genes isolated in this study are expressed in the developing otic capsule and/or neuroepithelium. Furthermore, the expression patterns also reveal molecular heterogeneity in the developing capsule and indicate that for some genes, the chondrogenic otic capsule is composed of distinct domains of gene expression.

The Schizosaccharomyces pombe rad31 and hus5 genes are required for the DNA damage response, as mutants defective in these genes are sensitive to DNA damaging agents, such as UV and ionising radiation and to the DNA synthesis inhibitor hydroxyurea (HU). Sequence analysis has suggested that rad31 and hus5 encode components of the Pmt3 (SUMO) modification process in S.pombe. We show here that the rad31 null and hus5.62 mutants display reduced levels of Pmt3 modification. We have initiated a search for proteins required for the DNA damage response, which may be modified by Pmt3 and have identified Rad22, the fission yeast homologue of the recombination protein Rad52. Purification of myc + His-tagged Rad22 protein from cells expressing HA-tagged Pmt3 identifies an 83 kDa species which cross-reacts with anti-HA antisera. We show here that Rad22 interacts with Rhp51 and Rpa70 (the fission yeast homologues of Rad51 and the large subunit of RPA, respectively), but that neither of these proteins appears to be responsible for the 83 kDa species. The 83 kDa species is observed when extracts are prepared under both native and denaturing conditions, and is also observed when myc + His-tagged Rad22 and Pmt3 are expressed at wild type levels, suggesting that Rad22 is modified by Pmt3 in vivo. We have established an S.pombe in vitro Pmt3 modification system and have shown that Rad22 and Rhp51 are modified in vitro, but that Rpa70 is not.