Evaluation of the level and radiosensitivity of the hematopoietic stem cell pool in man by the number of endocolonies of undifferentiated cells forming against a background of post-radiation bone marrow aplasia

The value and radiosensitivity of human haemopoietic stem pool may be assessed by the number of colonies of nondifferentiated cells (CFUnc) formed in situ during regeneration of the haemopoietic organ from the postirradiation aplasia. The time required for doubling the population, that constitutes nondifferentiated cell endocolonies, was reduced as the radiation dose increased.     

A sequence-based analysis of the pointer distribution of stichotrichous ciliates

Micronuclear genes in stichotrichous ciliates are broken into blocks separated by noncoding sequences, sometimes with the blocks in a shuffled order, some even inverted. During reproduction, all blocks are assembled in the correct order and orientation. This process is possible due to the special structure of micronuclear genes: each coding block M ends with a short nucleotide sequence (called pointer) that is repeated at the beginning of the coding block that should follow M in the assembled gene. Many of the pointers have multiple occurrences along both strands of the gene. This yields a very high number of pointer-induced possible divisions into coding and noncoding blocks.We investigate the distribution of pointers for all currently sequenced micronuclear ciliate genes with the goal of identifying what distinguishes the real gene structure among all possible coding/noncoding divisions. We find a sharp criterion in the average a/t-content of the noncoding blocks: the real division has, in most cases, the maximum such content among all possible combinations. Even for pointers as short as two nucleotides, the real division is one of very few with an average a/t-content of its noncoding blocks over 80%. The separation is most clear when the loci of pointers of up to four nucleotides (even three in the case of unscrambled genes) are fixed (e.g., through a template-based recombination mechanism).     

Changes in the cellular structure of the salivary glands in Chironomus larvae resulting from mechanical cell damage

Rapid morphological changes were observed in some cells of hand-isolated salivary glands of Ch. thummi larvae. The nuclear envelope, routinely closely fitting the tightly packaged polytene chromosomes, was seen to lose its contact with the chromosomes and to attain a smooth round shape. Then unfolding of the chromosomes occurred, their banding patterns becoming clearly evident, probably through widening the interband regions; the chromosome length increased by about 20%. We argue that the changes observed were induced during gland isolation by lesions of the cell basal envelope in the sites of the fat body connections to the salivary gland.     

Analysis of Spring Triticale Collection for Leaf Rust Resistance Genes with PCR Markers

Russian Journal of Genetics - The results of PCR analysis of the collection of spring triticale accessions for the presence of genes Lr9, Lr12, Lr19, Lr24, Lr25, Lr28, Lr29, and Lr47 (conferring...     

Functional and structural units in the chromomere

Electron microscopic observations demonstrate the existence of several DNA packing levels in the chromomere. A linear DNA molecule forms a big (chromomere) loop anchored to the chromosomal scaffold. The loop forms a set of smaller loops in the rosette pattern. Packing of the DNA by the histone octamer particles results in nucleosomes and nucleomeres. To establish the possible correspondence between the structural units of a chromomere and the genetical units (genes, exons, introns) in it, we compared the lengths of the units. Statistical analysis of the 315 sequenced genes indicate that the average gene size corresponds to the average length of a rosette loop. It means that a chromomere contains one or more genes. Assuming that exon-intron boundaries cannot bind nucleosomes we constructed DNA-packing models of the 88 genes. They demonstrate that the first (in 77.8 per cent of the genes) and the last (in 52.7 per cent) exons of the genes are too short to bind nucleosomes. Many genes contain long (nucleosome binding) pieces of DNA. Long packed pieces are introns in vertebrates; they are exons in invertebrates and plants. The average size gene contains two nucleomeres.