| Early embryos contain mRNA transcripts expressed from two distinct origins; those expressed from the mother's genome and deposited in the oocyte (maternal) and those expressed from the embryo's genome after fertilization (zygotic). The transition from maternal to zygotic control occurs at different times in different animals according to the extent and form of maternal contributions, which likely reflect evolutionary and ecological forces. Because zygotic transcripts can use both transcriptional and post-transcriptional mechanisms while maternal transcripts rely on post-transcriptional regulatory mechanisms these differences between animals may have associated regulatory consequences. We have used genomic data to identify and compare maternal and/or zygotic expressed genes from seven different animals and find evidence for selection acting to shape gene regulatory architecture. We find that mammalian maternal genes are enriched for complex regulatory regions suggesting an increase in specificity for expression. In contrast, the relative lack of specificity of maternal genes observed in egg-laying animals suggests that beyond nutritional content many maternal transcripts may be non-functional. These results provide clear predictive criteria for analysis of additional genomes. |
