Project description:A major challenge in biology is to determine how evolutionarily novel characters originate, however, mechanistic explanations for the origin of novelties are almost completely unknown. The evolution of mammalianM-BM- pregnancy is an excellent system in which to study the origin of novelties because extant mammals preserve major stages in the transition from egg-laying to live-birth. To determine the molecular bases of this transition we characterized the pregnant/gravid uterine transcriptome from tetrapods, including species in the three major mammalian lineages, and used ancestral transcriptome reconstruction to trace the evolutionary history of uterine gene expression. We show that thousands of genes evolved endometrial expression during the origins of mammalian pregnancy, including numerous genes that mediate maternal-fetal communication and immunotolerance.Furthermore we show that thousands of regulatory elements active inM-BM- decidualized human endometrial stromal cellsM-BM- are derived from ancient mammalian transposable elements which provided binding sites for transcription factors that mediate decidualization and endometrial cell-type identity.M-BM- Our results indicate that one of the defining mammalian novelties evolved via domestication of ancient mammalian transposable elements into hormone-responsive regulatory elements throughout the genome. Examination of histone modification and DNAse hypersensitivity in decidualized dESC
Project description:A major challenge in biology is to determine how evolutionarily novel characters originate, however, mechanistic explanations for the origin of novelties are almost completely unknown. The evolution of mammalian pregnancy is an excellent system in which to study the origin of novelties because extant mammals preserve major stages in the transition from egg-laying to live-birth. To determine the molecular bases of this transition we characterized the pregnant/gravid uterine transcriptome from tetrapods, including species in the three major mammalian lineages, and used ancestral transcriptome reconstruction to trace the evolutionary history of uterine gene expression. We show that thousands of genes evolved endometrial expression during the origins of mammalian pregnancy, including numerous genes that mediate maternal-fetal communication and immunotolerance.Furthermore we show that thousands of regulatory elements active in decidualized human endometrial stromal cells are derived from ancient mammalian transposable elements which provided binding sites for transcription factors that mediate decidualization and endometrial cell-type identity. Our results indicate that one of the defining mammalian novelties evolved via domestication of ancient mammalian transposable elements into hormone-responsive regulatory elements throughout the genome.
Project description:There are about 600 loci in the mammalian genome that are annotated as RNA polymerase III genes. These comprise tRNA genes, the genes encoding 5S RNA, the smallest ribosomal RNA, and genes encoding catalytic or structural RNAs involved in processes as diverse as RNA processing or transcription elongation. Most RNA polymerase III genes have similar promoter structures, yet they are transcribed with different efficiencies. Here we have explored how RNA polymerase III occupancy of these genomic loci varies in a normal tissue, the liver, during the transition from a resting state to a proliferating state. We find that after partial hepatectomy, which causes synchronous entry of remaining liver cells into the cell division cycle, there is a tremendous increase in RNA polymerase III occupancy. This increase is, however, not uniform and concerns mostly loci that were lowly occupied by RNA polymerase III in resting liver. The changes in RNA polymerase III occupancy cannot be correlated with changes in RNA polymerase II occupancy around the RNA polymerase III loci nor at nearby RNA polymerase II promoters. RNA polymerase III loci with the largest fold change tend to be located in clusters, with the cluster displaying the largest changes located on chromosome 13. This suggests that increases in RNA polymerase III occupancy during the transition from resting to proliferating state affect mostly genes whose basal rate of transcription is relatively low and which are located in clusters.