The evolution of gene expression in mammalian organ development remains largely uncharacterized. Here we report the transcriptomes of seven organs (cerebrum, cerebellum, heart, kidney, liver, ovary and testis) across developmental time points from early organogenesis to adulthood for human, macaque, mouse, rat, rabbit, opossum and chicken. Comparisons of gene expression patterns identified developmental stage correspondences across species, and differences in the timing of key events during the development of the gonads. We found that the breadth of gene expression and the extent of purifying selection gradually decrease during development, whereas the amount of positive selection and expression of new genes increase. We identified differences in the temporal trajectories of expression of individual genes across species, with brain tissues showing the smallest percentage of trajectory changes, and the liver and testis showing the largest. Our work provides a resource of developmental transcriptomes of seven organs across seven species, and comparative analyses that characterize the development and evolution of mammalian organs.

We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation.

These results highlight the importance of considering genetic factors in studies of risk factors for cardiovascular disease.

Immunological tolerance to self-antigen impairs humoral responses to HIV-1.

Computer simulation is a valuable tool in the genetic management of captive populations. It can be used to assess the extent of genetic variability in a colony, to predict the risk of future loss of variability, or to identify likely ancestral sources of traits of interest. "Gene dropping"tis a simulation procedure in which hypothetical alleles are assigned to each colon! founder, and a genotype is created for each descendant by Mendelian segregation of parental alleles. The gene dropping method is applied to analyses of four populations: (1) a colony of small South American marsupials, Monodelphis domesticu; (2) Speke's gazelles, Guzella spekei; (3) Przewalski's horses, Equus przewalskii; and (4) American Standardbred horses.