Evolutionary introduction of asymmetric cell division in regulative embryos

Earth hosts millions of species, allowing energy and nutrients to flow through the ecosystem and creating a vital environment for life to thrive. How did this diversity of life develop on Earth? This project addresses this fundamental question in cell and developmental biology by examining changes in the developmental programs of echinoderms, marine organisms such as sea urchins and sea stars, as a model system. Echinoderms are ideal models because embryos from each species are accessible and show gradual changes in their developmental programs depending on their evolutionary distances. For example, sea urchins are considered more derived than sea stars within echinoderms, with an evolutionary divergence estimated around 500 million years ago. The research focuses on a cell type called micromeres, which is unique to sea urchins and absent in other echinoderms. Micromeres act as a signaling center, significantly altering the developmental program in the sea urchin embryo. The research aims to understand how these unique cells evolved and their potential role in species divergence, therefore, seeking to explore the essential mechanisms that allow Earth to host millions of living organisms, including humans. Additionally, the project emphasizes outreach: sharing findings through laboratory tours, mentoring local students and teachers, and engaging undergraduate students in research. These efforts aim to promote scientific interest at various levels throughout the year. Mosaic embryos typically contain pre-localized factors in zygotes that determine embryonic polarity and cell fates. In contrast, regulative embryos have limited pre-localized factors, suggesting that another mechanism may control the establishment of initial polarity, which remains largely unknown. This research aims to identify the mechanism behind regulative embryonic development and how different species acquire distinct developmental styles, using echinoderm embryos as a model system. Aim 1 will examine how the regulation of conserved polarity factors involved in asymmetric cell divisions contributes to the initial establishment of polarity in the embryo, influencing the regulative nature of embryogenesis in the sea urchin. The researchers will perform overexpression and knockdown of polarity factors and cytoskeletal components, combined with time-lapse imaging during and after fertilization. These experiments will reveal how polarity factors and cytoskeletal elements regulate each other to establish embryonic polarity without pre-localized maternal factors. Aim 2 will investigate how the molecular evolution of polarity factors affects the divergence of developmental programs across different echinoderm species. This will be done through introduction of these factors into other echinoderm species to analyze changes in downstream developmental pathways, using single-cell (sc)RNA-seq and real-time imaging or fluorescent in situ hybridization (FISH) of key markers for development. Echinoderm embryos are ideal for this study because of their optical transparency and the well-understood effects of asymmetric cell division, which can be experimentally tested. Additionally, some echinoderms naturally exhibit an evolutionary transition in their developmental processes, making them an excellent model for comparative developmental biology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.