No abstract

DNA in situ hybridization with human chromosome specific DNA libraries was applied to compare the karyotypes of humans (Homo sapiens, 2n = 46) and cats (Felis catus, 2n = 38). For the autosomes alone, 30 segments of conserved synteny were revealed. The arrangement of these segments in the feline karyotype differs by only seven single chromosome breaks and one intrachromosomal inversion from their arrangement in humans. Comparison of these data with those recently obtained for pig and those available from conventional gene mapping studies in mice and cattle has allowed us to develop a model of karyotype evolution in mammals. The cat and human karyotypes, with 36 and 44 autosomes respectively, were found to be very similar to a putative ancient mammalian founder karyotype. It would appear that during evolution to the human karyotype the status quo has been conserved for at least some 100-120 million years. There has been no need to alter the well-balanced gene arrangement of the mammalian founder karyotype.

In evolutionary terms, insectivores are thought to be close to primates. Through ZOO-FISH analysis using human chromosome-specific painting probes, the syntenic relationship between the human and common shrew, Sorex araneus, karyotypes was studied. The human karyotype was found to be conserved in the shrew, with 32 autosomal segments of common synteny. Special arrangements, already known from similar studies on other species, were noted: fusions of HSA 16 and 19, HSA 3 and 21, and HSA 14 and 15. Only 10 breaks are necessary to transform the human karyotype into the karyotype of the common shrew. Together with known ZOO-FISH data from species belonging to other orders, this puts the human karyotype arrangement near the basis of all mammalian karyotypes. Human chromosome 2 was found to be conserved in its entirety as a single chromosome arm in the shrew. Evidence is presented that the same fusion of two original chromosomal segments formed the shrew chromosome ortholog of HSA 2 as the fusion that occurred during primate evolution to form human chromosome 2. This is a remarkable example of chromosomal coevolution.

The POU proteins BRN-3a, -3b and -3c are transcription factors encoded by separate genes that are differentially expressed during neural development. Comparison of genomic and cDNA sequences revealed similar exon/intron structures for Brn-3a and -3c genes, whereas the Brn-3b gene appeared to contain an intronless coding region. Fluorescence in situ hybridization experiments with mouse chromosomes showed that Brn-3a maps to mouse chromosome 14E1-3, Brn-3b to XF1-5 and Brn-3c to 18B3-E1.

Fragile sites are induced in chromosome 16 (band q22) of lymphocytes from some individuals, when the lymphocyte cultures are treated with the oligopeptide antibiotic distamycin A. These induced fragile sites are inherited in a Mendelian fashion; there are interfamilial differences in their appearance. The interactions between distamycin A and chromosomal DNA and the possible composition of the DNA at the induced fragile sites are discussed.