It was noted in the 19th century that morphological differences between species clearly increase — as animals became more advanced on the phylogenetic scale. Understanding the molecular foundations of these patterns (i.e starting from pluripotent embryonic stem cells, how does one cell ‘decide’ to turn into an organ such as brain vs heart vs kidney?) — should facilitate identification of general principles that underlie phenotypic evolution. “Evolution” continues to be a central theme in these GEITP pages.
Authors [see attached article] provide a resource of bulk transcriptomes (the sum total of all the messenger RNA molecules expressed from the genes of an organism, or in this case, within one organ) across developmental stages — covering seven organs from early organogenesis to adulthood in seven species, enabling direct comparisons of expression patterns in organ development within and across mammals (http://evodevoapp.kaessmannlab.org). This resource enabled the authors to analyze the evolution of gene expression within mammalian organs across all the developmental stages.
Specifically, the transcriptomes of cerebrum, cerebellum, heart, kidney, liver, ovary and testis were determined (from early organogenesis to adulthood) for human, rhesus macaque, mouse, rat, rabbit, opossum and chicken. Wow. Comparisons of gene expression patterns identified communications of the developmental stages across these species. Differences in the timing of key events during the development of the gonads were also revealed.
Authors 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, as development proceeds. Authors identified differences in the temporal trajectories of expression of individual genes across species. Brain tissues (both cerebrum and cerebellum) showed the smallest amount of trajectory changes, whereas liver and testis showed the largest percentage. These data should provide a resource — for every developmental biologist — of these developmental transcriptomes of seven organs across seven species. Comparative analyses that characterize the development and evolution of mammalian organs can now be scrutinized in much greater detail. 😊
Nature 25 July 2019; 571: 505-509