Allopolyploid origin and genome differentiation of the parasitic species Cuscuta veatchii (Convolvulaceae) revealed by genomic in situ hybridization

Interspecific hybridization and genome duplication to form allopolyploids are major evolutionary events in angiosperms. In the parasitic genus Cuscuta (Convolvulaceae), molecular data suggested the existence of species of hybrid origin. One of them, C. veatchii, has been proposed as a hybrid between C. denticulata and C. nevadensis, both included in sect. Denticulatae. To test this hypothesis, a cytogenetic analysis was performed with CMA/DAPI staining and fluorescent in situ hybridization using 5S and 35S rDNA and genomic probes. Chromosomes of C. denticulata were small with a well-defined centromeric region, whereas C. nevadensis had larger, densely stained chromosomes, and less CMA+ heterochromatic bands. Cuscuta veatchii had 2n = 60 chromosomes, about 30 of them similar to those of C. denticulata and the remaining to C. nevadensis. GISH analysis confirmed the presence of both subgenomes in the allotetraploid C. veatchii. However, the number of rDNA sites and the haploid karyotype length in C. veatchii were not additive. The diploid parentals had already diverged in their chromosomes structure, whereas the reduction in the number of rDNA sites more probably occurred after hybridization. As phylogenetic data suggested a recent divergence of the progenitors, these species should have a high rate of karyotype evolution.

New insights into the karyotype evolution of the genus Gampsocleis (Orthoptera, Tettigoniinae, Gampsocleidini)

Five species belonging to the genusGampsocleisFieber, 1852 were analyzed using fluorescencein situhybridization (FISH) with 18S rDNA and telomeric probes, as well as C-banding, DAPI/CMA3staining and silver impregnation. The studied species showed two distinct karyotypes, with 2n = 31 (male) and 2n = 23 (male) chromosomes. The drastic reduction in chromosome number observed in the latter case suggests multiple translocations and fusions as the main responsible that occurred during chromosome evolution. Two groups of rDNA distribution were found inGampsocleisrepresentatives analyzed. Group 1, with a single large rDNA cluster on the medium-sized autosome found in four species, carried in the haploid karyotype. Group 2, represented only byG.abbreviata, was characterized by the presence of two rDNA signals. TTAGG telomeric repeats were found at the ends of chromosome arms as expected. The rDNA clusters coincided with active NORs and GC-rich segments.

First karyological report in Larnax and Deprea (Solanaceae)

Somatic chromosomes of 12 samples belonging to seven Larnax Miers species and three Deprea Raf. species are studied. Chromosome number and karyotype analysis of both genera are reported for the first time. All taxa have 2n = 24. The most frequent haploid karyotype formula (8 of 12 samples) is 9 metacentric (m) + 3 submetacentric (sm) chromosomes, whereas L. glabra (Standl.) N.W. Sawyer and Larnax sp. display 10 m + 2 sm. Karyotypes of L. nieva S. Leiva & N.W. Sawyer and D. cuyacensis (N.W. Sawyer & S. Leiva) S. Leiva & Lezama are remarkable for the highest number of sm chromosome pairs, with 7 m + 5 sm and 5 m + 7 sm, respectively, presenting the highest intrachromosomal asymmetry index (A1), whereas Larnax sp. and L. glabra show the lowest A1. Most samples (9 of 12) examined have only one pair of chromosomes with nucleolar organiser regions (NOR), whereas L. glabra, Larnax sp., and D. cuyacensis possess two pairs of NOR. Systematic considerations about the monophyly of Larnax and Deprea are provided. The different karyotype parameters obtained, together with morphological characters, are discussed to single out the species.

Aneuploid yeast strains exhibit defects in cell growth and passage through START

Aneuploidy, a chromosome content that is not a multiple of the haploid karyotype, is associated with reduced fitness in all organisms analyzed to date. In budding yeast aneuploidy causes cell proliferation defects, with many different aneuploid strains exhibiting a delay in G1, a cell cycle stage governed by extracellular cues, growth rate, and cell cycle events. Here we characterize this G1 delay. We show that 10 of 14 aneuploid yeast strains exhibit a growth defect during G1. Furthermore, 10 of 14 aneuploid strains display a cell cycle entry delay that correlates with the size of the additional chromosome. This cell cycle entry delay is due to a delayed accumulation of G1 cyclins that can be suppressed by supplying cells with high levels of a G1 cyclin. Our results indicate that aneuploidy frequently interferes with the ability of cells to grow and, as with many other cellular stresses, entry into the cell cycle.

Karyological study in fifteen Leucocoryne taxa (Alliaceae)

The karyotype of fifteen Leucocoryne taxa was studied, assessing characteristics such as chromosome morphology and size, secondary constriction location, and asymmetry level. Two groups of Leucocoryne taxa were described based on chromosome number (2n = 10 and 2n = 18) and karyotype asymmetry. The haploid karyotype formula for the group 2n = 10 was 3m + 2st (or 2t), whereas for the group 2n = 18 was 7m + 2st (or 2t). Such results corroborate the karyotype descriptions previously carried out for some taxa of the genus. Leucocoryne taxa showed a high resemblance in chromosome morphology, but inter-specific differences were found in mean chromosome size. These data and previous studies based on gross chromosome morphology support Crosa’s hypothesis, which suggests that the cytotype 2n = 10 is diploid and perhaps ancestral, whereas that the cytotype 2n = 18 is tetraploid but with an additional chromosome fusion being probably a derived status.

Chromosome and pollen morphology of the rare endemic Centaurae lycopifolia Boiss. & Kotschy

Chromosome and pollen morphology of Centaurea lycopifolia Boiss. & Kotschy were studied. The chromosome number is 2n = 34 with haploid karyotype formula 9m + 9sm. Metaphase chromosome length ranging from 6.16 to 2.23 μm and the total haploid chromosome length was 65, 85 μm. The light and scanning electron microscope investigations revealed spheroidal-subprolate, the amb triangular and tricolporatae pollens in the taxon. Exine ornamentation was tectatae and microechinate-scabrate. Key words: Centaurea lycopifolia; Chromosome; Pollen morphology; Endemic; Turkey DOI: 10.3329/bjb.v39i2.7484 Bangladesh J. Bot. 39(2): 223-228, 2010 (December)

Is Genomic Imprinting Involved in the Pathogenesis of Hyperdiploid and Haploid Acute Lymphoblastic Leukemia of Childhood?

Hyperdiploidy with a chromosome number between 51 and 65 and a mean peak at 55 occurs as a distinct karyotype pattern in approximately 25-30% of ALLs in childhood [1, 2]. It is considered a favorable prognostic factor. The most intriguing cytogenetic peculiarities of these leukemias are the nearly exclusive presence of nonrandom numerical abnormalities due to the gain of chromosomes 4, 6, 10, 14, 17, 18, 20, 21 and X [1, 2]. In contrast, chromosomes 1, 2, 3, 12 and 16 are rarely involved [1, 2]. Typically, the affected chromosomes are present in three copies, with chromosome 21 also often being tetrasomic.Near-haploid cases, on the other hand, are extremely rare and have a bad prognosis [1, 2]. They contain at least one copy of each chromosome, a second copy of one of the sex chromosomes and both chromosomes 21 in most instances. In addition, two copies of chromosomes 10, 14 and 18 are commonly found.In the majority of cases of hyperdiploid ALL, the mechanism leading to the increased number of chromosomes is unknown. However, once formed, the abnormal karyotype is uniform and stable in the malignant cell population. Molecular genetic studies performed by Onodera et al. [3] revealed that the hyperdiploid karyotype usually arises by a simultaneous event during a single abnormal cell division from a diploid karyotype. Occasionally, this can also occur by doubling of the chromosomes from a near-haploid karyotype [4]. In virtually all cases, tetrasomy of chromosome 21 was generated by a duplication of both the maternally and paternally derived homolog. This finding was one of the main arguments for the notion that hyperdiploidy cannot be caused by stepwise or sequential gains from a diploid karyotype or by consecutive losses from a tetraploid karyotype.