title: Large scale comparison of global gene expression patterns in human and mouse.
abstract: BACKGROUND
  It is widely accepted that orthologous genes between species are conserved at the sequence level and perform similar functions in different organisms. However, the level of conservation of gene expression patterns of the orthologous genes in different species has been unclear. To address the issue, we compared gene expression of orthologous genes based on 2,557 human and 1,267 mouse samples with high quality gene expression data, selected from experiments stored in the public microarray repository ArrayExpress.
  
  
  RESULTS
  In a principal component analysis (PCA) of combined data from human and mouse samples merged on orthologous probesets, samples largely form distinctive clusters based on their tissue sources when projected onto the top principal components. The most prominent groups are the nervous system, muscle/heart tissues, liver and cell lines. Despite the great differences in sample characteristics and experiment conditions, the overall patterns of these prominent clusters are strikingly similar for human and mouse. We further analyzed data for each tissue separately and found that the most variable genes in each tissue are highly enriched with human-mouse tissue-specific orthologs and the least variable genes in each tissue are enriched with human-mouse housekeeping orthologs.
  
  
  CONCLUSIONS
  The results indicate that the global patterns of tissue-specific expression of orthologous genes are conserved in human and mouse. The expression of groups of orthologous genes co-varies in the two species, both for the most variable genes and the most ubiquitously expressed genes.
authors.affiliation: European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge CB10 1SD, UK. zheng@ebi.ac.uk
authors.forename: Xiangqun
authors.initials: X
authors.lastname: Zheng-Bradley
authors.forename: Johan
authors.initials: J
authors.lastname: Rung
authors.forename: Helen
authors.initials: H
authors.lastname: Parkinson
authors.forename: Alvis
authors.initials: A
authors.lastname: Brazma
mesh_terms: D000818:Animals; D016000:Cluster Analysis; D030541:Databases, Genetic; D015870:Gene Expression; D020869:Gene Expression Profiling / Q000379:methods*; D015894:Genome, Human; D006801:Humans; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D025341:Principal Component Analysis; D017422:Sequence Analysis, DNA / Q000379:methods