Primary mesenchyme cell-ring pattern formation in 2D-embryos of the sea urchin

Primary mesenchyme cell (PMC) migration during PMC-ring pattern formation w as analyzed using computer-assisted time-lapse video microscopy in spread e mbryos (2D-embryo) of the sea urchin, Mespilia globulus, and a computer sim ulation. The PMC formed a near normal ring pattern in the 2D-embryos, which were shown to be an excellent model for the examination of cell behavior i n vivo by time-lapse computer analysis. The average migration distance of t he ventro-lateral PMC aggregate-forming cells (AFC) and that of the dorso-v entral PMC cable-forming cells (CFC) showed no significant difference. All PMC took a rather straightforward migration path to their destinations with little lag time after ingression. This in vivo cell behavior fitted well t o a computer simulation with a non-diffusable chemotaxis factor in the cybe r-cell migration field. This simulation suggests that PMC recognize their d estination from a very early moment of cell migration from the vegetal plat e, and implicates that a chemoattractive region is necessary for making the PMC migration pattern. The left- and right-lateral AFC and dorso and ventr al CFC were each derived from an unequally divided one-quarter segment of t he vegetal plate. This suggests that AFC and CFC have a distinctive ancesto r in the vegetal plate, and the PMC are a heterogeneous population at least in terms of their destination in the PMC-ring pattern.