Diversity of satDNA fraction in Cestrum, the Genus with the Largest Genomes within Solanaceae

Cestrum species present large genomes (~24 pg), a high occurrence of B chromosomes, and great diversity in heterochromatin bands. Despite this, there is maintenance of chromosome shape and karyotype symmetry. To deepen our knowledge on Cestrum genome composition, low coverage sequencing data of C. strigilatum and C. elegans were compared. Bioinformatics analyses showed retrotransposons comprising more than 70% of the repetitive fraction, followed by transposons (~18%). The four satDNA families that accumulated the most in the datasets were used as probes in FISH assays, and showed different distribution profiles along chromosomes. Most hybridization signals were located in the C-CMA/DAPI banding sites, including those related to AT-rich Cold-Sensitive Regions (CSRs) and heterochromatin. Although satellite probes hybridized in all tested species, a satDNA family named CsSat49 was highlighted as it predominates in centromeric regions. Data suggest that the satDNA fraction is still conserved in the genus, although there is variation in the number of FISH signals between karyotypes, as well as in the B chromosomes. This study brings an important advance in the knowledge on genome organization and heterochromatin composition in Cestrum, especially on the distribution and differentiation mechanisms of satellite fraction between species of a genus of Solanaceae with large genomes.

Orcein and DAPI-stained karyotype analysis of Alocasia macrorrhizos (L.) G. Don

Karyotype analyses are required for the identification, characterization, and genetic improvement of any organism. Alocasia macrorrhizos (L.) G. Don. was investigated cytogenetically to determine the karyotypic features. Complex chromocenter type, of interphase nuclei, and gradient type of prophase chromosomes were found in this study. Alocasia macrorrhizos was found to possesses 2n=28 chromosomes. The total length of the 2n chromosome complement was recorded as 98.83±1.39 μm. The range of chromosomal length was 2.50±0.10-4.70±0.10 μm. A gradual decrease in chromosomal length was observed. The total form (TF%) value was found to be 43.58%, Karyotype symmetry index (Syi %) was 77.00 % and karyotype asymmetry index (AsK %) was 56.66%. The centromeric formula was 18m+4sm+2ac, representing asymmetric karyotype. In DAPI banding, the 1.48% positive banded region indicates the lower amount of AT rich repeats in this material. Therefore, Alocasia macrorrhizos could be authentically characterized through karyotype analysis. J. Bangladesh Acad. Sci. 45(1); 27-35: June 2021

Cytogenetic studies of three cultivated hill cotton (Gossypium arboreum L.) varieties from Bangladesh

Three hill cotton (Gossypium arboreum L.) varieties viz., HC-1, HC-2 and HC-3, released by Bangladesh Cotton Development Board were investigated through orcein, CMAand DAPI-banding for cytogenetical characterization and to elucidate the karyotypic diversity among these varieties. All these three varieties were found to possess 2n = 26 metacentric chromosomes with ‘1A’ karyotype. Based on TF%, AsK% and Syi index, HC-3 was little advanced over HC-1 and HC-2. These three varieties showed differential Chromomycin A3 (CMA)- and 4Ê-6 Diamidino-2-Phenyl Indole (DAPI)-banding patterns and a tendency of acumulation of repetitive sequences at the terminal regions was observed. Despite possessing same somatic chromosome number these three hill cotton varieties could be characterized by diversified karyotypic parameters through differential staining.

FIRST KARYOTYPE REPORT ON Colocasia oresbia: A COMPARATIVE CYTOGENETIC STUDY BETWEEN TWO VARIETIES

Karyotypes of two Colocasia oresbia botanical varieties from Bangladesh were analyzed and compared with orcein, chromomycin A3 (CMA) and 4´-6 diamidino-2-phenylindole (DAPI). Both varieties had 2n=2x=26 chromosomes (karyotypic formula: 20m+6sm) and a pair of satellites each. Total chromosome length was 144.18±2.45 μm in C. oresbia var. oresbia and 133.02±2.75 μm in C. oresbia var. stolonifera. The karyotype of Colocasia oresbia var. oresbia is 2A whereas that of C. oresbia var. stolonifera is 1A. Six CMA and four DAPI bands were observed in C. oresbia var. oresbia and eight CMA and six DAPI bands in C. oresbia var. stolonifera. However, in these two morphologically distinct C. oresbia varieties of two different ecological zones, the same somatic chromosome number, diversification in various karyotypic parameters and CMA/DAPI-banding patterns were observed. In addition to taxonomic characters, the studied karyotype features will contribute to the characterization of these two C. oresbia varieties and to establish a base for future research. Key words: chromosome banding; CMA; DAPI; Karyotype.

Integration of mandarin (Citrus reticulata) cytogenetic map with its genome sequence

Citrus is an extremely important genus in terms of world fruit production. Despite its economic importance and the small genome sizes of its species (2n = 18, 1C = 430 ± 68 Mbp), entire genomic assemblies have only recently become available for some of its representatives. Together with the previous CMA/DAPI banding and fluorescence in situ hybridization (FISH) in the group, these data are important for understanding the complex relationships between its species and for assisting breeding programs. To anchor genomic data with the cytogenetic map of mandarin (Citrus reticulata), the parental species of several economically important hybrids such as sweet orange and clementine, 18 BAC (bacterial artificial chromosome) clones were used. Eleven clementine BACs were positioned by BAC-FISH, doubling the number of chromosome markers so far available for BAC-FISH in citrus. Additionally, six previously mapped BACs were end-sequenced, allowing, together with one BAC previously sequenced, their assignment to scaffolds and the subsequent integration of chromosomes and the genome assembly. This study therefore established correlations between mandarin scaffolds and chromosomes, allowing further structural genomic and comparative study with the sweet orange genome, as well as insights into the chromosomal evolution of the group.

Advances in the cytogenetics of Annonaceae, the case of Annona cherimola L.

Annonaceae represent the largest extant family among the early divergent angiosperms. Despite the long-standing interest in its evolutionary and taxonomic aspects, cytogenetic studies on this family remain extremely few even on economically important species. With this study, we realized a detailed characterization of the chromosomes of Annona cherimola (2n = 14) by a combination of in situ hybridization techniques, fluorochrome banding, and karyomorphological analysis. FISH revealed that 45S and 5S rDNA sites are co-localized in correspondence to the secondary constrictions of the SAT-chromosome pair. Some hypotheses on the organization of the linked 45S and 5S rDNA repeats have been made. FISH with Arabidopsis-type telomeric arrays demonstrated that the A. cherimola telomeres are constituted by TTTAGGG sequences and that they are exclusively localized at the extremities of chromosomes. An insight into the chromosome structure of A. cherimola was obtained by the self-GISH procedure which revealed highly repeated DNA sequences localized in the centromeric regions of all chromosomes. The correspondence of s-GISH signals with DAPI banding suggests that these sequences are the principal component of the centromeric heterochromatin of this species. The karyotype of A. cherimola here described is proposed as the basic reference karyotype for successive investigations in Annonaceae.

Telomere length distribution on individual chromosome arms in patients with bronchial asthma

Objective. The purpose of this study was to evaluate the length of telomeres in the arms of individual chromosomes in patients with bronchial asthma (BA).Materials and methods. The study included patients with BA (n = 10, the mean age (44 ± 8.2) years) and healthy donors (n = 10, the mean age (44 ± 8.4) years). Metaphase spreads obtained from peripheral blood mononuclear cells were used. At the time of sampling BA patients received treatment at the Clinic of Immunopathology, Novosibirsk. BA was diagnosed by physicians according to GINA-2016. For measurement of telomere length on individual chromosome arms we used quantitative fluorescent in situ hybridization with a PNA-probe specific for telomeres. We used inverted DAPI banding for chromosome identification (according to ISCN-2013). For each individual 5 metaphase cells were analyzed. We applied the newly developed MeTeLen software to estimate the telomere repeats quantity (http:// www.bionet.nsc.ru/en/development/application-development/development-of-a-computer/metelen.html) in metaphase images. For enhanced image analysis compared with the previously developed programs, we included estimation of background signal and correction of defects of the optical system.Results. Comparing of telomere length show, that telomeres in the certain chromosome arms (4q, 5q, 9p, 10 q, 11p, 13p, 15q, 18q, 19q) in BA are significantly shorter than in corresponding group of donors (p < 0.05, Mann – Whitney U-test). For both studied groups we also evaluated telomere sequences shortened and elongated relative to the average telomere length in the group (p < 0.05, Wilcoxon-signed-runk test). The following differences and similarities between the telomere profiles of patients and donors were determined: the telomere sequences 4p, 6q, 8p were elongated and 2q, 9q, 11p, 15q were shortened relative to the average telomere length in BA patients. Moreover, this telomere sequences did not differ from the average telomere length in the group of donors. At the same time, the telomere sequences 12p, 16p, 17p, 19p were significantly shorter, and 3p was longer than the average telomere length in both groups.Conclusions. We guess, that the observed significant shortening of telomere length on individual chromosome arms in BA, as compared to donors, is relevant in pathogenesis of this disorder. The revealed features of telomere profile of patients with BA may be a result of different telomere length maintenance mechanisms and may influence to the development of asthma that needs further study.

FISH-based karyotyping of Pelmatohydra oligactis (Pallas, 1766), Hydra oxycnida Schulze, 1914, and H. magnipapillata Itô, 1947 (Cnidaria, Hydrozoa)

An account is given of the karyotypes of Hydramagnipapillata Itô, 1947, H.oxycnida Schulze, 1914, and Pelmatohydraoligactis (Pallas, 1766) (Cnidaria, Hydrozoa, Hydridae). A number of different techniques were used: conventional karyotype characterization by standard staining, DAPI-banding and C-banding was complemented by the physical mapping of the ribosomal RNA (18S rDNA probe) and H3 histone genes, and the telomeric (TTAGGG)n sequence by fluorescence in situ hybridization (FISH). We found that the species studied had 2n = 30; constitutive heterochromatin was present in the centromeric regions of the chromosomes; the “vertebrate” telomeric (TTAGGG)n motif was located on both ends of each chromosome and no interstitial sites were detected; 18S rDNA was mapped on the largest chromosome pair in H.magnipapillata and on one of the largest chromosome pairs in H.oxycnida and P.oligactis; in H.magnipapillata, the major rRNA and H3 histone multigene families were located on the largest pair of chromosomes, on their long arms and in the centromeric areas respectively. This is the first chromosomal mapping of H3 in hydras.