Project description:Transposable elements (TEs) are genetic parasites that can potentially threaten the stability of the genomes they colonize. Nonetheless, TEs persist within genomes and are rarely fully eliminated, diverse TE families coexisting in various copy numbers. The TE replication strategies that enable host organisms to tolerate and accommodate the extensive diversity of TEs, while minimizing harm to the host and avoiding mutual competition among TEs, remain poorly understood. Here, by studying the spontaneous or experimental mobilization of four Drosophila LTR RetroTransposable Elements (LTR-RTEs), we reveal that each of them preferentially targets open chromatin regions characterized by specific epigenetic features. Among these, gtwin and ZAM are expressed in distinct cell types within female somatic gonadal tissues and inserted into the distinct accessible chromatin landscapes of the corresponding stages of embryogenesis. These findings suggest that individual LTR-RTEs exploit unique biological niches, enabling their coexistence within the tightly regulated ecosystem of the same host genome.
Project description:The emergence of the hematopoietic system occurs in temporal waves across different tissues during mouse development. During these waves, the endothelial niche serves as a source of hematopoietic cells and provides molecular cues that potentially shape the tissue-specific lineage output. Although the endothelial-to-hematopoietic transition in the aorta-gonad-mesonephros is well understood, a systematic analysis of hematopoietic progenitors and their endothelial niche across fetal tissues is lacking. Here, we leverage single-cell RNA-sequencing of micro-dissected fetal tissues during their peak of hematopoietic activity to systematically compare hematopoietic progenitors and the endothelial niche. We predict stage-specific interactions accompanying the transition of yolk sac endothelium to primitive and definitive hematopoietic fates and reveal distinct roles for fetal liver vascular niches. Furthermore, we provide in vitro evidence that lipid signaling by sphingosine-1-phosphate producing erythrocyte progenitors supports hematopoietic stem cell expansion in fetal liver. Our resource deciphers the temporal waves of hematopoietic development within distinct vascular niches.