UC San Diego

The development of the sea urchin larval body plan is well-understood from extensive studies of embryonic patterning. However, fewer studies have investigated the late larval stages during which the unique pentaradial adult body plan develops. Ancestral and evolved traits exist both in the larval and juvenile echinoderm body plans, so studying juvenile development is necessary to understand echinoderm evolution. In chapter 1, we apply hybridization chain reaction (HCR) in situs to the fast-developing and transparent sea urchin Lytechinus pictus, with a focus on skeletogenic cells. First, we use HCR to provide a detailed staging scheme for the localization of skeletogenic cells around the rudiment and show that many skeletogenic cells unassociated with larval rods appear outside of the rudiment prior to appearing inside. Second, we find co-expression of blastocoelar and skeletogenic cell markers around juvenile skeleton located outside of the rudiment, which is consistent with data showing that cells from the non-skeletogenic mesoderm embryonic lineage reprogram into juvenile skeletogenic cells. Third, we show that downstream biomineralization genes have similar expression patterns during larval and juvenile skeletogenesis, suggesting some conservation of skeletogenic mechanisms in the larva and juvenile. In chapter 2, we use a fluorescent protein that is bright when injected into L pictus and identify cell-type specific reporters to provide tools to lineage trace and understand cell movement prior to and during metamorphosis. This work sets the foundation for subsequent studies of the late larva of L. pictus to better understand juvenile body plan development, patterning, and evolution.