Chromatin condensation dynamics and implications of induced premature chromosome condensation

Somatic cell cycle is a dynamic process with sequential events that culminate in cell division. Several physiological activities occur in the cytoplasm and nucleus during each of the cell cycle phases which help in doubling of genetic content, organized arrangement of the duplicated genetic material and perfect mechanism for its equal distribution to the two daughter cells formed. Also, the cell cycle checkpoints ensure that the genetic material is devoid of damages thus ensuring unaltered transmission of genetic information. Two important phenomena occurring during the cell cycle are the DNA condensation and decondensation cycles in the nucleus along with the cyclic expression and functioning of certain specific proteins that help in the same. Several protein families including Cyclins, cyclin dependent kinases, condensins, cohesins and surivins ensure error free, stage specific DNA condensation and decondensation by their highly specific, controlled orchestrated presence and action. Understanding the molecular mechanisms of chromatin compaction towards formation of the structural units, the chromosomes, give us valuable insights into the cellular physiology and also direct us to techniques such as premature chromosome condensation. The techniques of inducing ‘prophasing’ of interphase cells are undergoing rapid advances which have multidimensional applications for basic research and direct applications.     

Chondrichthyan cytogenetics: A comparison with teleosteans

Summary Cytogenetic studies on cartilaginous fish conducted in recent years have shown that these vertebrates have peculiarities associated both with the karyotypes and the size and composition of their DNAs. Although the data for this group, which includes about 1000 extant species, are still fragmentary, there appear to be more differences than similarities with teleosts; e.g., chromosome sets are characterized by a high diploid number (2n=up to 106) and are often rich in acrocentric elements and in microchromosomes. From the quantitative standpoint, chondrichthyan genomes are relatively large (2C=up to 34 pg DNA/n), exhibiting sometimes wide interspecific variability (Squalidae).The few studies on genome composition for these species have revealed marked difference between chondrichthyans and teleosteans in the ratio of the amount of GC-rich DNA to the total increase in genome. Moreover, thermal denaturation of the genomes of six selachians revealed derived curves that are characteristic of heterogeneity in nucleotide distribution, which has not been evidenced in most of the teleosteans investigated thus far.Finally, for the first time in selachians, an investigation was conducted using restriction enzymes, the results of which showed a pattern of chromosome labeling that was in some cases (Alu I) similar to and in others (Hae III, Hind III) different from that of teleosteans.     

Water Buffalo Genome Science Comes of Age

The water buffalo is vital to the lives of small farmers and to the economy of many countries worldwide. Not only are they draught animals, but they are also a source of meat, horns, skin and particularly the rich and precious milk that may be converted to creams, butter, yogurt and many cheeses. Genome analysis of water buffalo has advanced significantly in recent years. This review focuses on currently available genome resources in water buffalo in terms of cytogenetic characterization, whole genome mapping and next generation sequencing. No doubt, these resources indicate that genome science comes of age in the species and will provide knowledge and technologies to help optimize production potential, reproduction efficiency, product quality, nutritional value and resistance to diseases. As water buffalo and domestic cattle, both members of the Bovidae family, are closely related, the vast amount of cattle genetic/genomic resources might serve as shortcuts for the buffalo community to further advance genome science and biotechnologies in the species.     

Somaclonal variation — a novel source of variability from cell cultures for plant improvement

Summary It is concluded from a review of the literature that plant cell culture itself generates genetic variability (somaclonal variation). Extensive examples are discussed of such variation in culture subclones and in regenerated plants (somaclones). A number of possible mechanisms for the origin of this phenomenon are considered. It is argued that this variation already is proving to be of significance for plant improvement. In particular the phenomenon may be employed to enhance the exchange required in sexual hybrids for the introgression of desirable alien genes into a crop species. It may also be used to generate variants of a commercial cultivar in high frequency without hybridizing to other genotypes.     

Synthesis, morphology and cytogenetics of Raphanofortii (TTRR, 2n = 38): a new amphidiploid of hybrid Brassica tournefortii (TT, 2n = 20) ×Raphanus caudatus (RR, 2n=18)

Amphidiploid Raphanofortii was synthesized by colchicinization of the F₁ hybrid Brassica tournefortii (TT, 2n = 20)×Raphanus caudatus (RR, 2n = 18). The crossability between these two species, and the cytomorphology of the F₁ plants and the amphidiploids were investigated. Intergeneric hybrids between the species were obtained only when B. tournefortii was involved as female parent. The hybrid plants were intermediate for most of the morphological attributes and showed very low pollen fertility compared to the parents. Although a majority of the pollen mother cells of the dihaploid hybrid (TR, 2n = 19) harboured univalents, a maximum of six bivalents were also observed. Of the 37 colchicine-treated F₁ plants analyzed cytologically, 21 were found to be true amphidiploids (2n = 38), whereas seven were mixoploids. Meiosis in the amphidiploids was characterized by the occurrence of 19 bivalents, though multivalents and univalents were also observed in a few cells. Most of the amphidiploid plants exhibited a fairly high pollen and seed fertility, which was further enhanced with the advancement of generations. Out of 69 plants investigated in the A₂ generation, 64 were euploids while the remaining five were aneuploids (2n = 36, 37, 39, 40 and 42). The newly synthesized Raphanofortii has great potential as a new commercial crop, as well as a bridge species for the transfer of economically important attributes of both the species to other Brassicas. Received: 2 November 1999 / Accepted: 26 March 2000     

Relationships between the completion of first cleavage and the chromosomal complement,sex, and developmental rates of bovine embryos generated in vitro

One thousand eighty-four two-cell bovine embryos produced from 1,574 oocytes matured and fertilized in vitro were cultured as groups separated according to the time when they completed their first cleavage (24,30,40,48, or 62 hr postinsemination; hpi). At 5 days after insemination, the proportions of each group that had progressed to the eight-cell stage or beyond were determined and the 350 that had done so were fixed and examined cytogenetically for cell number, chromosomal abnormalities, and sex. Embryos in the “early” cleaving (24 and 30 hpi) and “late” cleaving (40–62 hpi) groups were compared. Early cleaving embryos were more likely to have developed to the eight-cell stage or beyond (52.2% vs. 20%), contained more cells (22 vs. 17), and were more likely to be male (3.6:1 vs. 0.93:1). It is suggested that these phenotypic differences between the sexes begin before the embryonic genome is generally thought to become activated and are due either to differential processing of X- and Y-bearing sperm within the zygote or to very early differential expression of genes derived from X- and Y-bearing sperm. © 1993 Wiley-Liss, Inc.     

Biologic,Immunocytochemical, and Cytogenetic Characterization of Two New Human Melanoma Cell Lines: IIB-MEL-LES and IIB-MEL-IAN

Two human melanoma cell lines, derived from metastases of two patients with epithelioid malignant amelanotic melanomas, and designated IIB-MEL-LES and IIB-MEL-IAN, have been established. Both cell lines have been in continuous culture over 2 years and were propagated continuously for 85 and 75 serial passages, respectively. Morphologically, IIB-MEL-LES is composed predominantly of spindle shaped cells, whereas IIB-MEL-IAN grows as a monolayer of cuboid and stellate shaped cells with many rounded cells in suspension. Immunocytochemical studies revealed that both cell lines express S-100 protein, vimentin, and GD₃ and GD₂ gangliosides but are negative for keratin and collagen. Both cell lines express HLA class I and HLA-DR antigens in variable proportions. The MAGE-1 gene is expressed only by the IIB-MEL-IAN cell line, as revealed by PCR analysis. Cytogenetic analysis of both cell lines revealed abnormal karyotypes; the modal chromosome numbers of IIB-MEL-LES and IIB-MEL-IAN were 48 and 81, respectively. IIB-MEL-LES cells presented rearrangements in chromosomes 1, 14 and X, gains in chromosomes 10,20, and 21 losses in chromosomes 15 and Y. The most frequent markers observed in IIB-MEL-IAN cells were 7q+, 10p+, 2p+, i(6p), 2q+, and 10q-. Clonal gains were observed in chromosomes 12 and 21, whereas losses were seen in chromosomes 1, 2, 3, 4, 6, 7, 11, and 17. Both cell lines were capable of forming colonies in soft agar and developed tumors when transplanted into nude mice, reproducing and maintaining the characteristics of the original tumors. These cell lines and their xenografts appear to provide useful systems for studying the biology, genetics and histogenesis of human malignant melanoma and could be utilized for the development of melanoma vaccines.