Chromosome 21

About: Chromosome 21 is a research topic. Over the lifetime, 4736 publications have been published within this topic receiving 206655 citations. The topic is also known as: chr21 & Homo sapiens chromosome 21.

Chromosome territory arrangement and homologous pairing in nuclei of Arabidopsis thaliana are predominantly random except for NOR-bearing chromosomes

Abstract: Differential painting of all five chromosome pairs of Arabidopsis thaliana revealed for the first time the interphase chromosome arrangement in a euploid plant. Side-by-side arrangement of heterologous chromosome territories and homologous association of chromosomes 1, 3 and 5 (on average in 35-50% of nuclei) are in accordance with the random frequency predicted by computer simulations. Only the nucleolus organizing region (NOR)-bearing chromosome 2 and 4 homologs associate more often than randomly, since NORs mostly attach to a single nucleolus. Somatic pairing of homologous approximately 100 kb segments occurs less frequently than homolog association, not significantly more often than expected at random and not simultaneously along the homologs. Thus, chromosome arrangement in Arabidopsis differs from that in Drosophila (characterized by somatic pairing of homologs), in spite of similar genome size, sequence organization and chromosome number. Nevertheless, in up to 31.5% of investigated Arabidopsis nuclei allelic sequences may share positions close enough for homologous recombination.

Growth and development of the brain in Down syndrome.

Abstract: The brain of a child with Down syndrome develops differently from a normal one, attaining a form reduced in size and altered in configuration. Directly related to the mental retardation are neuronal modifications manifest as alterations of cortical lamination, reduced dendritic ramifications, and diminished synaptic formation. However, selected cholinergic marker enzymes such as choline acetyl transferase and acetyl cholinesterase have shown no alterations in young children with Down syndrome. The pace of the neuronal transformations is related to stage of maturation. With early growth and development, the normal dendritic tree continuously expands. In Down syndrome, at 4 months of age, the neurons show a relatively expanded dendritic tree, but during the first year the dendrites stop growing and become atrophic relative to control neurons. Accompanying these neuronal irregularities are subtle alterations of other cell types: astrocyte, oligodendrogliocyte, microglia, and endothelial cell. In early infancy, one of the astrocytic markers, GFAP, is not altered, but there is greater expression of S-100 protein in the temporal lobe in Down syndrome. Oligodendrogliocyte dysfunction is reflected in delayed myelination in pathways of frontal and temporal lobes. Microglia appear more prominent in Down syndrome. A minority of children with Down syndrome have vascular dysplasias and focal calcification of basal ganglia. In young children, expression of beta-amyloid in Down syndrome is no different than in normal children but disappears after age two, only to reappear in adults. As some of these studies suggest, the identification of genes on chromosome 21 and the determination of the gene product allow the production of specific antibodies and, through immunohistochemical techniques, the identification of the expression of these proteins in both normal development and Down syndrome. Specifically, the localization and appearance in development of proteins such as the beta-subunit of S-100, beta-amyloid (A4 protein), superoxide dismutase, and OK-2 are providing the means for better understanding the morphogenesis of the cellular and eventually molecular basis for the mental retardation in Down syndrome.

Human chromosome 21 gene expression atlas in the mouse

Abstract: Genome-wide expression analyses have a crucial role in functional genomics. High resolution methods, such as RNA in situ hybridization provide an accurate description of the spatiotemporal distribution of transcripts as well as a three-dimensional 'in vivo' gene expression overview. We set out to analyse systematically the expression patterns of genes from an entire chromosome. We chose human chromosome 21 because of the medical relevance of trisomy 21 (Down's syndrome). Here we show the expression analysis of all identifiable murine orthologues of human chromosome 21 genes (161 out of 178 confirmed human genes) by RNA in situ hybridization on whole mounts and tissue sections, and by polymerase chain reaction with reverse transcription on adult tissues. We observed patterned expression in several tissues including those affected in trisomy 21 phenotypes (that is, central nervous system, heart, gastrointestinal tract, and limbs). Furthermore, statistical analysis suggests the presence of some regions of the chromosome with genes showing either lack of expression or, to a lesser extent, co-expression in specific tissues. This high resolution expression 'atlas' of an entire human chromosome is an important step towards the understanding of gene function and of the pathogenetic mechanisms in Down's syndrome.

Mapping of human chromosomal regions related to neoplasia: evidence from chromosomes 1 and 17.

Abstract: In clonal aberrations leading to an excess or partial excess of chromosome 1, trisomy for bands 1q25-1q32 was noted in the myeloid cells from all of 34 patients who had various disorders such as acute leukemia, polycythemia vera, and myelofibrosis. This was not the result of a particularly fragile site in that region of the chromosome because the break points in reciprocal translocations that involve it occurred almost exclusively in the short arm. Two consistent rearrangements that have been observed in chromosome 17 produced either duplication of the entire long arm or a translocation of the distal portion of the long arm to chromosome 15. The nonrandom chromosomal changes found in hematologic disorders can now be correlated with the gene loci on these chromosomes or chromosomal segments. Seventy-five genes related to various metabolic enzymes have been mapped; it may be significant that chromosomes carrying gene loci related to nucleic acid metabolism are more frequently involved in hematologic disorders (and other malignancies as well) than are gene loci related to intermediary or carbohydrate metabolism. Furthermore, the known virus-human chromosome associations are closely correlated with the chromosomes affected in hematologic disorders. If one of the effects of carcinogens (including viruses) is to activate genes that regulate host cell DNA synthesis, and if translocations or duplications of specific chromosomal segments produce the same effect, then either of these mechanisms might provide the affected cell with a proliferative advantage.