Nature and distribution of constitutive heterochromatin in fishes,genus Hypostomus (Loricariidae)

Some Hypostomus species were studied concerning the features of the karyotype structure and the constitutive heterochromatin. The karyotype of Hypostomus sp. F from the S?o Francisco river (Minas Gerais state, Brazil) is now described for the first time. A diversity in the diploid number, ranging from 2n = 68 to 2n = 80, as well as in the karyotype formulae, is evident in this fish group. Two types of heterochromatin, GC- and AT-rich, could be identified with the use of base-specific fluorochromes. In some species heterochromatic bands are mainly located on the centromeric and telomeric chromosomal regions, while in other species they are also observed at interstitial locations. Hypotheses concerning this heterochromatic distribution in Hypostomus karyotypes are discussed. A case of supernumerary heterochromatic segment and a centric fusion appear to be related with two variant karyotypic formulae observed among specimens from the Mogi-Gua?u and S?o Francisco rivers, respectively. The available data permit us to characterize a divergent karyotypic evolution among the Hypostomus species already analyzed, both at the macro- and microstructural levels, that is, their general karyotype organization and particular features related to chromosomal banding or staining, respectively.     

黄芪复合体（豆科）核型研究补充材料

本文首次报道了民和黄芪的染色体数目及核型。发现该种与黄芪复合体其它类群的染色体数目相同,但核型有别,其核型公式为２ｎ＝１６＝８ｍ（２ＳＡＴ）＋８ｓｍ。这种核型变异与它的形态变异一致。在黄芪复合体内,每一类群的染色体至少具１对随体,且附着在最后１对染色体的短臂上（除蒙古黄芪具２对随体外）,而Ｔｏｈ（１９７１）报道采自Ｋｙｕｎｇｉ和Ｍｔ．Ｈａｒｌａ膜荚黄芪和高山膜荚黄芪（新拟）的染色体不具随体,可能观察有误。     

Karyotypic changes in potato plants regenerated from protoplasts

Over two hundred plants were regenerated from shoot-culture derived proto-plasts of potato (Solanum tuberosum L. cv. Majestic). Some had grossly aberrant phenotypes but the majority were similar to, or indistinguishable from normal control Majestic. Cytological examination showed that on average, 57% of the regenerants had the normal chromosome number (2n=4x=48). The remainder were aneuploids and fell into two classes in approximately equal numbers. The first class was limited at about the euploid level (ie, 2n=44–49). The second class contained plants with higher chromosome numbers ranging from 2n=73 to the octaploid level (2n=8x=96). The overall results represent an improvement over our earlier studies on chromosome variation in protoplast-derived potato plants. In addition, three cases of structural chromosome variation were observed.     

Astyanax hastatus Myers, 1928 (Teleostei,Characidae): A new species complex within the genus Astyanax?

Four populations of Astyanax hastatus Myers 1928 from the Guapimirim River basin (Rio de Janeiro State) were analyzed and three distinct cytotypes identified. These cytotypes presented 2n = 50 chromosomes, with 4M+8SM+10ST+28A (Cytotype A), 8M+10SM+14ST+18A (Cytotype B), 6M+8SM+4ST+32A (Cytotype C) and scanty heterochromatin, mainly located throughout pericentromeric regions of several chromosomal pairs. No homologies with the As-51 satellite DNA were observed in the three cytotypes, although all of them presented multiple 18S rDNA sites, as detected by both silver nitrate staining and FISH (fluorescent in situ hybridization). The application of the term "species complex" in Astyanax is discussed from a cytotaxonomic viewpoint.     

Mip1 associates with both the Mps1 kinase and actin,and is required for cell cortex stability and anaphase spindle positioning

The Mps1 family of protein kinases contributes to cell cycle control by regulating multiple microtubule cytoskeleton activities. We have uncovered a new Mps1 substrate that provides a novel link between Mps1 and the actin cytoskeleton. We have identified a conserved human Mps1 (hMps1) interacting protein we have termed Mps1 interacting protein-1 (Mip1). Mip1 defines an uncharacterized family of conserved proteins that contain coiled-coil and calponin homology domains. We demonstrate that Mip1 is a phosphoprotein that interacts with hMps1 in vitro and in vivo and is a hMps1 substrate. Mip1 exhibits dynamic localization during the cell cycle; Mip1 localizes to the actin cytoskeleton during interphase, the spindle in early mitosis, and the cleavage furrow during cytokinesis. Mip1 function is required to ensure proper spindle positioning at the onset of anaphase after cells begin furrow ingression. Cells depleted of Mip1 exhibit aberrant mitotic actin filament organization, excessive membrane blebbing, dramatic spindle rocking, and chromosome distribution errors during early cytokinesis producing high numbers of binucleate cells. Our data indicate that Mip1 is a newly recognized component of the actin cytoskeleton that interacts with hMps1 and that it is essential to ensure proper segregation of the genome during cell cleavage.     

Chromosome characterization and variability in some Iridaceae from Northeastern Brazil

The chromosomes of 15 species of Iridaceae of the genera Alophia, Cipura, Eleutherine, Neomarica and Trimezia (subfamily Iridoideae) were examined after conventional Giemsa staining. The karyotypes of Alophia drummondii (2n = 14+1B, 28, 42 and 56), Cipura paludosa (2n = 14), C. xanthomelas (2n = 28) and Eleutherine bulbosa (2n = 12) were asymmetric; Neomarica candida, N. caerulea, N. humilis, N. glauca, N. gracilis, N. northiana and Neomarica sp. (2n = 18); N. cf. paradoxa (2n = 28), Trimezia fosteriana (2n = 52), T. martinicensis (2n = 54) and T. connata (2n = 82) were all generally symmetric. New diploid numbers of 2n = 56 for Alophia drummondii, 2n = 18 for N. candida, N. humilis, N. glauca, and N. gracilis, 2n = 28 for N. cf. paradoxa, and 2n = 82 for T. connata are reported. The karyotypic evolution of the studied species is discussed.     

Genomic consequences of interspecific Pinus spp. hybridization

Strong karotypic orthoselection does not fully account for genome size variation in pines. Adult F1 interspecific pine hybrids are fertile and the genomic consequences of hybridization can be studied using haploid female megagametophytes. Greater variation in genome size was hypothesized to occur in hybrids compared to their parental species and the variation was thought to be positively related to the phylogenetic distance between the parental species. Nuclear 1C DNA content of megagametophytes from four sets of fertile Pinus spp. F1 hybrids and their parents was determined using a laser flow cytometer. Fertile F1 hybrids included two sets of hard pine hybrid Pinus elliottii Engelm. x P. caribaea var. hondurensis Morelet and two Asian x New World soft pine hybrids P. wallichiana A.B. Jacks. x P. strobus L. (hybrid is known as P. x schwerinii ) and P. lambertiana Dougl. x P. armandii Franchlet. Fertile, adult F1 produce haploid megagametophytes with nuclear DNA contents comparable to the parents or parental species. One genomic consequence of hybridization in pines is stability in nuclear DNA content. Hybrid genomes neither increased or decreased DNA content regardless of the phylogenetic distance between parents. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 503–508.     

Unprecedented chromosomal diversity and behaviour modify linkage patterns and speciation potential: structural heterozygosity in an Australian spider

The Huntsman spider Delena cancerides shows an extraordinary level of chromosomal diversity and meiotic complexity. Some populations form normal bivalents at male meiosis, but 14 populations form chains of chromosomes. Six of these populations form two chains, and so show segregation behaviour which is beyond our current understanding of meiotic processes. Chromosomal variation of this sort is rarely tolerated in other species, because the segregation of long chromosome chains frequently results in gametes with too many or too few chromosomes. The resulting reproductive failure may form the basis for reproductive isolation in many species, and so the mechanisms that allow D. cancerides to segregate long chromosome chains have allowed this species to maintain cohesion despite extensive chromosomal variation over its range. The effect these chromosome chains have on the population genetics of the species is discussed, and a model for the evolution of the system is proposed.     

Chromosome studies in Hippeastrum (Amaryllidaceae): variation in genome size

This paper presents the karyotype and DNA content of 12 diploid species of Hippeastrum from South America. The variation in genome size is compared with the karyotype and DNA content of Amaryllis belladonna from South Africa. The Hippeastrum species present a uniform and bimodal basic karyotype formula, but significant differences are found in the total chromosome volume (TCV) and nuclear DNA content. A positive correlation between the DNA content and TCV is also observed. The karyotype's constancy is a product of changes in DNA content occurring in the whole chromosome complement. The DNA addition to the long and short sets of chromosomes varies independently. In species with higher DNA contents, the short chromosomes add equal DNA amounts to both arms, maintaining their metacentric morphology, whereas the long chromosomes add DNA only to the short arm, increasing the chromosome symmetry. These data show that the evolutionary changes in DNA amount are proportional to chromosome length, maintaining the karyotypic uniformity. A. belladonna has a larger DNA content and possesses a karyotype different from that of Hippeastrum spp., supporting the distinction between the two genera and upholding the name Amaryllis for the South African entity against Hippeastrum for the South American genus.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 171–178.     

Comparative cytogenetics in Apareiodon affinis (Pisces, Characiformes) and considerations regarding diversification of the group

Comparative cytogenetic studies in Apareiodon affinis (Pisces, Characiformes) from two hydrographic Brazilian basins showed significant divergences related to the general karyotype structure, C‐banding and nucleolar organizer region (NOR) bearing chromosomes. In the upper Paraná basin population, distinct diploid numbers were observed among sexes, the females showing 2n = 55 and the males 2n = 54 chromosomes, characterizing a multiple sex chromosome system of the ZZ/ZW₁W₂ type. A diploid number equal to 54 chromosomes was found for the Cuiabá river population, without a sex chromosome heteromorphism. However, the occurrence of acrocentric chromosomes represents an unique character for this population. These karyotypic differences indicate that the analyzed populations must represent distinct Apareiodon species. This revised version was published online in July 2006 with corrections to the Cover Date.