title: Migration of sea urchin primordial germ cells.
abstract: BACKGROUND
  Small micromeres are produced at the fifth cleavage of sea urchin development. They express markers of primordial germ cells (PGCs), and are required for the production of gametes. In most animals, PGCs migrate from sites of formation to the somatic gonad. Here, we investigated whether they also exhibit similar migratory behaviors using live-cell imaging of small micromere plasma membranes.
  
  
  RESULTS
  Early in gastrulation, small micromeres transition from non-motile epithelial cells, to motile quasi-mesenchymal cells. Late in gastrulation, at 43 hr post fertilization (HPF), they are embedded in the tip of the archenteron, but remain motile. From 43-49 HPF, they project numerous cortical blebs into the blastocoel, and filopodia that contact ectoderm. By 54 HPF, they begin moving in the plane of the blastoderm, often in a directed fashion, towards the coelomic pouches. Isolated small micromeres also produced blebs and filopodia.
  
  
  CONCLUSIONS
  Previous work suggested that passive translocation governs some of the movement of small micromeres during gastrulation. Here we show that small micromeres are motile cells that can traverse the archenteron, change position along the left-right axis, and migrate to coelomic pouches. These motility mechanisms are likely to play an important role in their left-right segregation.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Campanale
authors.forename: Tufan
authors.initials: T
authors.lastname: Gökirmak
authors.forename: Jose A
authors.initials: JA
authors.lastname: Espinoza
authors.forename: Nathalie
authors.initials: N
authors.lastname: Oulhen
authors.forename: Gary M
authors.initials: GM
authors.lastname: Wessel
authors.forename: Amro
authors.initials: A
authors.lastname: Hamdoun
mesh_terms: D000818:Animals; D002465:Cell Movement / Q000502:physiology; D005854:Germ Cells / Q000166:cytology*; D011554:Pseudopodia / Q000502:physiology; D012617:Sea Urchins / Q000166:cytology* / Q000502:physiology
keywords: cortical bleb; filopodia; live cell imaging; migration; motility; phosphoinositides; primordial germ cell; small micromere