Additional Author(s): Jeffrey R.Thompson, Elizabeth Petsios, Eric Erkenbrack, Rex A. Moats, David J.Bottjer, and Eric H. Davidson
Tools & Techniques: Visualizing Genes/ Proteins
Endoderm-derived: Digestive (Gut) Tract
Mesoderm-derived: Muscle; Skeleton
Organism: Sea Urchin
Stage of Development: Larva/Juvenile
This in situ hybridization image is a horizontal cross-section of a 3 weeks post-metamorphosis juvenile pencil urchin (Eucidaris tribuloides). Juvenile skeletogenesis is visualized by expression of sm37, a skeletogenesis gene. At this stage you can see expression in the developing sea urchin shell called a test—particularly the test wall (tw). In addition, sm37 is expressed in the definitive spine (ds) and tubercle (tu)—the skeletal element on which spines mount. Spines provide protection for the sea urchin. The chewing machinery of the sea urchin is called Aristotle’s lantern. Its skeletal components are the teeth (t) and hemipyramids (h). Finally, sm37 is expressed in the pedicellaria (pe), a claw-like defensive structure of the urchin. There is no sm37 expression in the juvenile spine (which has stopped growing by this time; js), spine ligament (sl), epidermis (ep), lantern tracting muscle (lt), interpyramidal muscle (im), gut (g), or pharynx (ph). Further, it is not expressed in the tube feet (also called podia; po) or water canal (wc) which are part of the water vascular system that enables the sea urchin to move.
Gao F, Thompson JR, Petsios E, Erkenbrack E, Moats RA, Bottjer DJ, Davidson EH. Juvenile skeletogenesis in anciently diverged sea urchin clades. Dev Biol. 2015, 400(1):148-58.