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  • 1
    ISSN: 1573-6849
    Keywords: FISH ; Fugu rubripes ; heterochromatin ; Huntingtin ; NOR ; pufferfish ; replication banding ; Tetraodon nigroviridis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Because of its highly compact genome, the pufferfish has become an important animal model in genome research. Although the small chromosome size renders chromosome analysis difficult, we have established both classical and molecular cytogenetics in the freshwater pufferfish Tetraodon nigroviridis (TNI). The karyotype of T. nigroviridis consists of 2n = 42 biarmed chromosomes, in contrast to the known 2n = 44 chromosomes of the Japanese pufferfish Fugu rubripes (FRU). RBA banding can identify homologous chromosomes in both species. TNI 1 corresponds to two smaller FRU chromosomes, explaining the difference in chromosome number. TNI 2 is homologous to FRU 1. Fluorescence in-situ hybridization (FISH) allows one to map single-copy sequences, i.e. the Huntingtin gene, on chromosomes of the species of origin and also on chromosomes of the heterologous pufferfish species. Hybridization of total genomic DNA shows large blocks of (species-specific) repetitive sequences in the pericentromeric region of all TNI and FRU chromosomes. Hybridization with cloned human rDNA and classical silver staining reveal two large and actively transcribed rRNA gene clusters. Similar to the situation in mammals, the highly compact pufferfish genome is endowed with considerable amounts of localized repeat DNAs.
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  • 2
    ISSN: 1573-6849
    Keywords: COPG2 ; Fugu rubripes ; imprinting ; MEST ; Tetraodon nigroviridis ; UCN
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We isolated Fugu genomic clones using the human MEST (Mesoderm-Specific Transcript) cDNA as probe. Sequence analysis revealed the presence of MEST and three additional genes which show homology to plant DNBP (DNA-Binding Protein), vertebrate COPG2 (Coat Protein Gamma 2), as well as to human and mouse UCN (Urocortin). Structures of Fugu and human MEST, COPG2 and UCN genes are very similar. Since MEST and COPG2 are neighboring genes on human chromosome 7q32, we can conclude that we identified their orthologs and that linkage of these genes is evolutionarily conserved in vertebrates. Unlike human MEST which underlies isoform-specific imprinting and is methylated in a parent-of-origin-specific fashion, the CpG island of the Fugu ortholog is completely methylated. The translation start of Fugu MEST is identical to the non-imprinted human isoform which is in good agreement with the assumption that genomic imprinting is restricted to mammals. Comparative mapping of these genes by fluorescence in-situ hybridization to metaphase chromosomes of Fugu rubripes and Tetraodon nigroviridis showed clear signals on one of the smallest acrocentric chromosomal pairs, which in Fugu, can be easily classified by its unique triangular shape.
    Type of Medium: Electronic Resource
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