Masa-Toshi Yamamoto

Mutations in orbit/mast reveal that the central spindle is comprised of two microtubule populations, those that initiate cleavage and those that propagate furrow ingression

We address the relative roles of astral and central spindle microtubules (MTs) in cytokinesis of Drosophila melanogaster primary spermatocytes. Time-lapse imaging studies reveal that the central spindle is comprised of two MT populations, “interior” central spindle MTs found within the spindle envelope and “peripheral” astral MTs that probe the cytoplasm and initiate cleavage furrows where they contact the cortex and form overlapping bundles. The MT-associated protein Orbit/Mast/CLASP concentrates on interior rather than peripheral central spindle MTs. Interior MTs are preferentially affected in hypomorphic orbit mutants, and consequently the interior central spindle fails to form or is unstable. In contrast, peripheral MTs still probe the cortex and form regions of overlap that recruit the Pav-KLP motor and Aurora B kinase. orbit mutants have disorganized or incomplete anillin and actin rings, and although cleavage furrows initiate, they ultimately regress. Our work identifies a new function for Orbit/Mast/CLASP and identifies a novel MT population involved in cleavage furrow initiation.

Hybrid lethal systems in the Drosophila melanogaster species complex

Lethal phases of the hybrids betweenDrosophila melanogaster and its sibling species,D. simulans are classified into three types: (1) embryonic lethality in hybrids carryingD. simulans cytoplasm andD. melanogaster X chromosome, (2) larval lethality in hybrids not carryingD. simulans X, and (3) temperature-sensitive pupal lethality in hybrids carryingD. simulans X. The same lethal phases are also observed when either of the two other sibling species,D. mauritiana orD. sechellia, is employed for hybridization withD. melanogaster. Here, we describe genetic analyses of each hybrid lethality, and demonstrate that these three types of lethality are independent phenomena. We then propose two models to interpret the mechanisms of each hybrid lethality. The first model is a modification of the conventional X/autosome imbalance hypothesis assuming a lethal gene and a suppressor gene are involved in the larval lethality, while the second model is for embryonic lethality assuming an interaction between a maternal-effect lethal gene and a suppressor gene.

Proteome mapping of the Drosophila melanogaster male reproductive system

The fruit fly Drosophila melanogaster is an excellent model organism for studying insect reproductive biology. Although the gene expression profiles of both male and female reproductive organs have been studied in detail, their proteomic profiles and functional characteristics largely remained to be clarified. In this study, we conducted proteome mapping of the male internal reproductive organs using 2‐DE. We identified a total of 440 protein components from gels of the male reproductive organs (testis, seminal vesicle, accessory gland, ejaculatory duct, and ejaculatory bulb). A number of proteins associated with odorant/pheromone‐binding, lipid metabolism, proteolysis, and antioxidation were expressed tissue specifically in the male reproductive system. Based on our proteomic data set, we constructed reference proteome maps of the reproductive organs, which will provide valuable information toward a comprehensive understanding of Drosophila reproduction.

Cytogenetical localization of Zygotic hybrid rescue (Zhr), a Drosophila melanogaster gene that rescues interspecific hybrids from embryonic lethality

Hybrid females from crosses between Drsophila melanogaster males and females of its sibling species, D. simulans, D. mauritiana, or D. sechellia die as embryos. This lethality is believed to be caused by incompatibility between the X chromosome of D. melanogaster and the maternal cytoplasm. Zygotic hybrid rescue (Zhr) prevents this embryonic lethality and has been cytogenetically mapped to a proximal region of the X chromosome of D. melanogaster, probably in the centromeric heterochromatin. We have carried out high resolution cytological mapping of Zhr using deficiencies and duplications of the X heterochromatin. Deletions of the Zhr+ gene from the hybrid genome exhibit the Zhr phenotype. On the contrary, addition of the wild-type gene to the hybrid genome causes embryonic lethality, regardless of sex. The Zhr locus has been narrowed down to the region covered by Dp(1;f)1162 but not covered Dp(1;f)1205, a chromosome carrying a duplication of heterochromatin located slightly distal to the In(1)sc8 heterochromatic breakpoint.

Genomic dispersion of 28S rDNA during karyotypic evolution in the ant genusMyrmecia (Formicidae)

The chromosomal localization of 28S rDNA was investigated in 16 speices of the Australian ant genus Myrmecia, with 2n numbers ranging from 4 to 76, using the fluorescence in situ hybridization method and karyographic analysis. A unique phenomenon was observed: the number of chromosomes carrying 28S rDNA increases from 2 in species with low chromosome numbers to 19 in species with high chromosome numbers. This is termed rDNA dispersion. Centric fission and a reciprocal translocation that occurs in C-bands were detected as the major mechanisms involved in rDNA dispersion.

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex

AbstractChromosomal localization of rDNA in samples of five taxa of the Myrmecia pilosula species complex (Hymeoptera: Formicidae: Myrmeciinae) with 2n=3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsorum), and 27 (M. pilosula) was carried out by fluorescence in situ hybridization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the coding region for 28S rRNA. Results show that (1) the 28S rDNA in the genome of these ants is repetitive and is localized in pericentromeric C-bands, (2) the number of chromosomes carrying rDNA is two in M. croslandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pilosula, and (3) only one or two clusters of rRNA genes generate nucleoli in each species. We suggest that the rDNA in the ancestral stock of the M. pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission. Most rDNA multiplied on various chromosomes seems to be inactivated and eliminated from the genome, together with C-bands, by

NBRP databases: databases of biological resources in Japan.

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Two novel Pao-like retrotransposons (Kamikaze and Yamato) from the silkworm species Bombyx mori and B. mandarina: common structural features of Pao-like elements.

-inversion or centric fusion, with the remnant rDNAs dispersed in the genome by centric fission and