Report of the third international workshop on human chromosome 10 mapping and sequencing 1999

Neurophysiological findings in a newborn with chromosome 10 trisomy

The trisomy of the short arm of chromosome 10 is a rare condition. The phenotypic expression of this genetic aberration is characterised by growth and mental retardation with several neurological signs. We report the neurophysiological findings in a newborn affected by 10p chromosome trisomy who developed seizures. Serial EEGs showed a progressive reduction in burst-suppression activity and a slow rhythmic basal activity. At 1 year of age the recording showed for the first time spikes of high amplitude (up to 800 μV) in bilateral frontal regions. These findings could be related to an asymmetrical cerebral maturation in the context of perinatal sufferance and brain malformation due to the genetic aberration.

The DNA sequence and comparative analysis of human chromosome 10

The finished sequence of human chromosome 10 comprises a total of 131,666,441 base pairs. It represents 99.4% of the euchromatic DNA and includes one megabase of heterochromatic sequence within the pericentromeric region of the short and long arm of the chromosome. Sequence annotation revealed 1,357 genes, of which 816 are protein coding, and 430 are pseudogenes. We observed widespread occurrence of overlapping coding genes (either strand) and identified 67 antisense transcripts. Our analysis suggests that both inter- and intrachromosomal segmental duplications have impacted on the gene count on chromosome 10. Multispecies comparative analysis indicated that we can readily annotate the protein-coding genes with current resources. We estimate that over 95% of all coding exons were identified in this study. Assessment of single base changes between the human chromosome 10 and chimpanzee sequence revealed nonsense mutations in only 21 coding genes with respect to the human sequence.

Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA

We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and sub-fractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a K(m) of 41.9 micro M and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution.

Human paralogs of KIAA0187 were created through independent pericentromeric-directed and chromosome-specific duplication mechanisms

KIAA0187 is a gene of unknown function that maps to 10q11 and has been subject to recent duplication events. Here we analyze 18 human paralogs of this gene and show that paralogs of exons 14-23 were formed through satellite-associated pericentromeric-directed duplication, whereas paralogs of exons 1-9 were created via chromosome-specific satellite-independent duplications. In silico, Northern, and RT-PCR analyses indicate that nine paralogs are transcribed, including four in which KIAA0187 exons are spliced onto novel sequences. Despite this, no new genes appear to have been created by these events. The chromosome 10 paralogs map to 10q11, 10q22, 10q23.1, and 10q23.3, forming part of a complex family of chromosome-specific repeats that includes GLUD1, Cathepsin L, and KIAA1099 pseudogenes. Phylogenetic analyses and comparative FISH indicates that the 10q23.1 and 10q23.3 repeats were created in 10q11 and relocated by a paracentric inversion 13 to 27 Myr ago. Furthermore, the most recent duplications, involving the KIAA1099 pseudogenes, have largely been confined to 10q11. These results indicate a simple model for the evolution of this repeat family, involving multiple rounds of centromere-proximal duplication and dispersal through intrachromosomal rearrangement. However, more complex events must be invoked to account for high sequence identity between some paralogs.