TY - JOUR T1 - Developmental constraints on genome evolution in four bilaterian model species JF - bioRxiv DO - 10.1101/161679 SP - 161679 AU - Jialin Jiu AU - Marc Robinson-Rechavi Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/07/12/161679.abstract N2 - Developmental constraints on genome evolution have been suggested to follow either an early conservation model or an "hourglass" model. Both models agree that late development (after the morphological ‘phylotypic’ period: both late and post-embryonic development) diverges between species, but debate on which developmental period is the most conserved. Here, based on a modified “Transcriptome Age Index” approach, we analyzed the constraints acting on three evolutionary traits of protein coding genes (strength of purifying selection on protein sequences, phyletic age, and duplicability) in four species: C. elegans, D. melanogaster, D. rerio and M. musculus. In general, we found that both models can be supported from different genomic properties. The evolution of phyletic age and of duplicability follow an early conservation model in all species, but sequence evolution follows different models in different species: an hourglass model in both D. rerio and M. musculus, and an early conservation model in D. melanogaster. Further analyses indicate that stronger purifying selection on sequences in the early development (before the morphological ‘phylotypic’ period) of D. melanogaster and in the middle development (the morphological ‘phylotypic’ period) of D. rerio are driven by temporal pleiotropy of these genes. In addition, inspired by the “new genes out of the testis” hypothesis, we report evidence that expression in late development is enriched with retrogenes. This implies that expression in late development could facilitate transcription, and eventually acquisition of function, of new genes. Thus, it provides a model for why both young genes and high duplicability genes trend to be expressed in late development. Finally, we suggest that dosage imbalance could also be one of the factors that cause depleted expression of young genes and of high duplicability genes in early development, at least in C. elegans. ER -