Centromere protein A (Cenpa for mouse, CENP-A for other species) is a histone H3-like protein that is thought to be involved in the nucleosomal packaging of centromeric DNA. Using gene targeting, we have disrupted the mouse Cenpa gene and demonstrated that the gene is essential. Heterozygous mice are healthy and fertile whereas null mutants fail to survive beyond 6.5 days postconception. Affected embryos show severe mitotic problems, including micronuclei and macronuclei formation, nuclear bridging and blebbing, and chromatin fragmentation and hypercondensation. Immunofluorescence analysis of interphase cells at day 5.5 reveals complete Cenpa depletion, diffuse Cenpb foci, absence of discrete Cenpc signal on centromeres, and dispersion of Cenpb and Cenpc throughout the nucleus. These results suggest that Cenpa is essential for kinetochore targeting of Cenpc and plays an early role in organizing centromeric chromatin at interphase. The evidence is consistent with the proposal of a critical epigenetic function for CENP-A in marking a chromosomal region for centromere formation.

There is a growing interest in the use of semiconductor quantum dots as fluorescent markers in biological applications. However, there are concerns regarding the potential environmental impact and toxic nature of these nanomaterials. In this study, we have investigated the interaction of water-soluble semiconductor quantum dots with supercoiled DNA.

CENP-B is a constitutive centromere DNA-binding protein that is conserved in a number of mammalian species and in yeast. Despite this conservation, earlier cytological and indirect experimental studies have provided conflicting evidence concerning the role of this protein in mitosis. The requirement of this protein in meiosis has also not previously been described. To resolve these uncertainties, we used targeted disruption of the Cenpb gene in mouse to study the functional significance of this protein in mitosis and meiosis. Male and female Cenpb null mice have normal body weights at birth and at weaning, but these subsequently lag behind those of the heterozygous and wild-type animals. The weight and sperm content of the testes of Cenpb null mice are also significantly decreased. Otherwise, the animals appear developmentally and reproductively normal. Cytogenetic fluorescence-activated cell sorting and histological analyses of somatic and germline tissues revealed no abnormality. These results indicate that Cenpb is not essential for mitosis or meiosis, although the observed weight reduction raises the possibility that Cenpb deficiency may subtly affect some aspects of centromere assembly and function, and result in reduced rate of cell cycle progression, efficiency of microtubule capture, and/or chromosome movement. A model for a functional redundancy of this protein is presented.

Dystrophin coordinates the assembly of a complex of structural and signaling proteins that are required for normal muscle function. A key component of the dystrophin protein complex is ␣-dystrobrevin, a dystrophinassociated protein whose absence results in neuromuscular junction defects and muscular dystrophy. To gain further insights into the role of ␣-dystrobrevin in skeletal muscle, we used the yeast two-hybrid system to identify a novel ␣-dystrobrevin-binding partner called syncoilin. Syncoilin is a new member of the intermediate filament superfamily and is highly expressed in skeletal and cardiac muscle. In normal skeletal muscle, syncoilin is concentrated at the neuromuscular junction, where it colocalizes and coimmunoprecipitates with ␣-dystrobrevin-1. Expression studies in mammalian cells demonstrate that, while ␣-dystrobrevin and syncoilin associate directly, overexpression of syncoilin does not result in the self-assembly of intermediate filaments.Finally, unlike many components of the dystrophin protein complex, we show that syncoilin expression is upregulated in dystrophin-deficient muscle. These data suggest that ␣-dystrobrevin provides a link between the dystrophin protein complex and the intermediate filament network at the neuromuscular junction, which may be important for the maintenance and maturation of the synapse.