Genomics

The DNA sequence and comparative analysis of human chromosome 20. Deloukas, P. et al. Nature 414, 865–871 (2001) [PubMed]

This paper reports the completion of the sequence of the euchromatic portion of human chromosome 20, and the analysis and annotation of the sequence. The value of having finished sequence available is highlighted by the finding of several discrepancies between these results and those reported last year in the draft human sequence analysis. The authors boosted their gene-prediction and gene-annotation analyses by using whole-genome shotgun data from two other vertebrates, the mouse and the pufferfish.

Epigenetics

Differentially methylated forms of histone H3 show unique association patterns with inactive X chromosomes. Boggs, B. A. et al. Nature Genet. 30, 73–76 (2002) [PubMed]

Histone H3 lysine 9 methylation is an epigenetic imprint of facultative heterochromatin. Peters, A. H. et al. Nature Genet. 30, 77–80 (2002) [PubMed]

Mammalian X-chromosome inactivation is an ideal model for studying the link between histone methylation and epigenetic gene regulation, as investigated in these studies. Both teams used antibodies against the methylated form of Lys9 on histone H3 (H3–Lys9) to show that this methylated residue is enriched in heterochromatin on inactive human X chromosomes. As it is retained during mitosis and chromosome condensation, this methylated residue might be a stably propagated epigenetic mark for the inactive X. As Peters et al. found, it is also retained in the absence of the histone methyltransferase, Suv39, in female mouse cells, which abolished H3–Lys9 methylation in constitutive but not in facultative heterochromatin, indicating that a Suv39-independent pathway regulates H3–Lys9 methylation in facultative heterochromatin.

Complex disease

Independent genome-wide scans identify a chromosome 18 quantitative-trait locus influencing dyslexia. Fisher, S. E. et al. Nature Genet. 30, 86–91 (2002) [PubMed]

For conditions such as dyslexia, which have an important genetic component, but are also highly heterogeneous, it is very difficult to identify the key genetic loci. Fisher et al. have tackled this problem with a QTL-based approach in which individuals are assessed using quantitative criteria related to word recognition. In a genome-wide scan, they find evidence to support previous reports of a dyslexia locus on chromosome 6, but also find new QTL, in particular one on chromosome 18.