CHARACTERIZATION OF HUMAN CHROMOSOMAL CONSTITUTIVE HETEROCHROMATIN

Heterochromatin of centromeric chromosome regions contains late replicating, largely repetitive DNA. It is suggested that heterochromatin participates in chromosome pairing, crossing-over and in chromosome disjunction control (1,3). Centromeric heterochromatin, a variety of heterochromatin, is a tightly packed form of DNA.Centromeric heterochromatin is a constituent in the formation ofactive centromeres in most higher-order organisms; the domain exists on both mitotic and interphase chromosomes. (4,5,6,8) Centromeric heterochromatin is usually formed on alpha satellite DNA in humans; however, there have been cases where centric heterochromatin and centromeres have formed on originally euchromatin domains lacking alpha satellite DNA; this usually happens as a result of a chromosome breakage event and the formed centromere is called a neocentromere.

Intertwined Functions of Separase and Caspase in Cell Division and Programmed Cell Death

Timely sister chromatid separation, promoted by separase, is essential for faithful chromosome segregation. Separase is a member of the CD clan of cysteine proteases, which also includes the pro-apoptotic enzymes known as caspases. We report that the C. elegans separase SEP-1, primarily known for its role in cell division, is required for apoptosis when the predominant pro-apoptotic caspase CED-3 is compromised. Loss of SEP-1 results in extra surviving cells in a weak ced-3(−) mutant, and suppresses the embryonic lethality of a mutant defective for the apoptotic suppressor ced-9/Bcl-2. We also report apparent non-apoptotic roles for CED-3 in promoting germ cell proliferation and germline meiotic chromosome disjunction and the normal rate of embryonic development. Moreover, loss of the soma-specific (CSP-3) and germline-specific (CSP-2) caspase inhibitors results in CED-3-dependent suppression of embryonic lethality and meiotic chromosome non-disjunction respectively, when separase function is compromised. Thus, while caspases and separases have evolved different substrate specificities associated with their specialized functions in apoptosis and cell division respectively, they appear to have retained the residual ability to participate in both processes, supporting the view that co-option of components in cell division may have led to the innovation of programmed cell suicide early in metazoan evolution.

Caryopathic effect of bio-preparation Bacillus subtilis 12В on the status of spermatogenic epithelium of animals infected with helminths

Objective of research: to study the caryopathic effect of bio-preparation Bacillus subtilis 12В on the status of spermatogenic epithelium of white mice after a single intra-abdominal administration of the Fasciola hepatica extract. Materials and methods: The investigations were conducted on white male mice after oral use of preparation Sporovite based on B. subtilis 12B; then the intra-abdominal injection of F. hepatica extracts at a dose of 100 mkg/head was applied. The protein extract from F. hepatica was administered to mice of the second group, and animals of the third group received only the probiotic Sporovite. Animals of the fourth group did not get the preparation and served as controls. 48 hours later the animals were killed; touch smears obtained from testis were stained by the Romanovsky method and examined under a microscope what enables to determine the mitotic index and the number of pathological meiosis forms. The experiments were conducted on lambs whose seminal vesicles were placed into a solution of 10% Formalin and examined histologically. 2-3μ-thick slices were stained with Haematoxylin and Eosin by Van Gieson method and examined under a microscope at 50, 400 and 1000 x magnifications. Results and discussion: During the pathomorphological and caryomitotic studies of testis of white mice and lambs after administration of Sporovite on the background of intra-abdominal injection of F. hepatica extract the reduction of negative effects on the status of spermatogenic epithelium of testis in animals wasn’t observed. A decrease in mitotic index by 2-3 times and a high amount of pathological forms were registered. The number of metaphases with preterm chromosome disjunction under the joint effect of F. hepatica and B. subtilis extracts has decreased by half.

Live observation of fission yeast meiosis in recombination-deficient mutants

Regular segregation of homologous chromosomes during meiotic divisions is essential for the generation of viable progeny. In recombination-proficient organisms, chromosome disjunction at meiosis I generally occurs by chiasma formation between the homologs (chiasmate meiosis). We have studied meiotic stages in living rec8 and rec7 mutant cells of fission yeast, with special attention to prophase and the first meiotic division. Both rec8 and rec7 are early recombination mutants, and in rec7 mutants, chromosome segregation at meiosis I occurs without any recombination (achiasmate meiosis). Both mutants showed distinct irregularities in nuclear prophase movements. Additionally, rec7 showed an extended first division of variable length and with single chromosomes changing back and forth between the cell poles. Two other early recombination deficient mutants (rec14 and rec15) showed very similar phenotypes to rec7 during the first meiotic division, and the fidelity of achiasmate chromosome segregation slightly exceeded the expected random level. We discuss possible regulatory mechanisms of fission yeast to deal with achiasmate chromosome segregation.

Suppressed Recombination and a Pairing Anomaly on the Mating-Type Chromosome of Neurospora tetrasperma

Neurospora crassa and related heterothallic ascomycetes produce eight homokaryotic self-sterile ascospores per ascus. In contrast, asci of N. tetrasperma contain four self-fertile ascospores each with nuclei of both mating types (matA and mata). The self-fertile ascospores of N. tetrasperma result from first-division segregation of mating type and nuclear spindle overlap at the second meiotic division and at a subsequent mitotic division. Recently, Merino et al. presented population-genetic evidence that crossing over is suppressed on the mating-type chromosome of N. tetrasperma, thereby preventing second-division segregation of mating type and the formation of self-sterile ascospores. The present study experimentally confirmed suppressed crossing over for a large segment of the mating-type chromosome by examining segregation of markers in crosses of wild strains. Surprisingly, our study also revealed a region on the far left arm where recombination is obligatory. In cytological studies, we demonstrated that suppressed recombination correlates with an extensive unpaired region at pachytene. Taken together, these results suggest an unpaired region adjacent to one or more paired regions, analogous to the nonpairing and pseudoautosomal regions of animal sex chromosomes. The observed pairing and obligate crossover likely reflect mechanisms to ensure chromosome disjunction.

The presence of synaptic and chromosome disjunction mutants in Cenchrus ciliaris (Poaceae: Paniceae)

Synaptic mutants are present in Cenchrus ciliaris L This species, due to the presence of linear bivalents and occasion­al trivalents and quadrivalents, is an intermediate desynaptic species. In addition, geographical distribution and environmental factors, such as high temperatures and low humidity, could also have had an influence on the desynapsis observed.The disjunction of chromosomes during anaphase I was mostly abnormal in this desynaptic species. Precocious disjunction of chromosomes into chromatids occurred during anaphase I Due to the high incidence of this chromosome abnormality, a mutant gene, 'pc' responsible for the disjunction of chromosomes, must be present. The absence of cytokinesis in one specimen indicates a recessive mutant gene, 'va' to be active in this species.