Developmental fates of the first four blastomeres of the chaetognath Paraspadella gotoi: relationship to protostomes.
Experimental analysis of the development of chaetognaths is virtually lacking. To elucidate developmental fates, single blastomeres of the 2-cell and 4-cell embryos of Paraspadella gotoi were injected with a lineage-tracing dye (Fluoro-Ruby or DiI). The distribution of the labels was observed in the hatchlings. In a previous study, embryos were injected at the 2-cell stage with Fluoro-Ruby and two sets of complementary labeling patterns (DL and VR, and DR and VL) were found. The same results were obtained when DiI was used as a tracer dye. The 4-cell embryo consists of the animal and vegetal cross-furrow cells in a tetrahedral arrangement and one of the vegetal cross-furrow cells typically contains the germ plasm. When single cells were injected at the 4-cell stage, four labeling patterns were observed (D, V, L and R). These four patterns represent subsets of the four patterns observed in the hatchling injected at the 2-cell stage. The V pattern is probably generated from the blastomere containing the germ plasm. It was found that the positions of the blastomeres at the 4-cell stage corresponded to the future body axes, similar to classic spiralians and modified spiralians such as crustaceans. Furthermore, it was confirmed that second cleavage occurs in a leiotropic fashion, which is seen in the second cleavage of the classic spiralians. Chaetognaths may have some similarities to protostomes in their developmental program.
Shimotori
T
T
Department of Biology, Faculty of Education, Mie University, Tsu, Mie 514-8507, Japan.
Goto
T
T
D000818:Animals; D001757:Blastomeres / Q000502:physiology*; D019521:Body Patterning / Q000502:physiology; D002232:Carbocyanines / Q000378:metabolism; D019070:Cell Lineage / Q000502:physiology*; D003911:Dextrans / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D007448:Invertebrates / Q000196:embryology* / Q000502:physiology; D012235:Rhodamines / Q000378:metabolism
C035005:3,3'-dihexadecylindocarbocyanine; D002232:Carbocyanines; D003911:Dextrans; D005456:Fluorescent Dyes; C067661:Fluoro-Ruby; D012235:Rhodamines