Embryonic origin of adult pluripotent stem cells and anatomical systems during planarian embryogenesis

Division Of Basic Sciences - Nci

Investigators

Abstract

We generated a whole-animal scRNA-seq time course data from S. polychroa embryos and young juveniles, Stage 5 (S5) through Juvenile 2 (J2). This data set captures developmental milestones including establishment of the adult body axes, construction of adult anatomical systems, and acquisition of whole-body regeneration competence. Vital embryonic cells in all cell cycle phases were profiled from nine stages, each with two biological replicates. All major anatomical systems (except the reproductive system) are represented in the time course. We are annotating cell clusters using GO term analysis, custom cell-type modules comprised of transcripts with documented tissue-specific expression patterns, and cross-species comparisons with whole-animal S. mediterranea scRNA-Seq atlases using SAMap. To achieve finer granularity, we are subsetting and re-clustering data for major anatomical systems to maximize recovery of molecular signatures for transitional cell states and emerging cell types during development. Through comparisons with S. mediterranea, we anticipate assignation of gene expression signatures for more than 100 distinct cell types/states. We will leverage transcriptional heterogeneity among cycling stem cells to characterize the progenitor repertoire fueling construction of the adult anatomy, and we will document whether or how progenitor subpopulations change during development. Moving forward, we will perform trajectory analysis to generate in silico hypotheses about lineage differentiation programs originating from cycling embryonic stem cells and adult neoblasts. Trajectories will be made for major anatomical systems (e.g., the musculature system), as well as the embryonic stem cell-to-neoblast transition. Our data suggests that major adult lineages are established by Stage 5 that they remain in use throughout embryogenesis. We hypothesize that transcriptional modules used for adult anatomy construction during development remain in use during adulthood for neoblast-driven tissue homeostasis and the regeneration. Comparisons of lineage differentiation programs at different developmental stages will suggest strategies used by planarians, and potentially other animals, to support indeterminate growth and regenerative capacity throughout life.