title: Krüppel-like is required for nonskeletogenic mesoderm specification in the sea urchin embryo.
abstract: The canonical Wnt pathway plays a central role in specifying vegetal cell fate in sea urchin embryos. SpKrl has been cloned as a direct target of nuclear beta-catenin. Using Hemicentrotus pulcherrimus embryos, here we show that HpKrl controls the specification of secondary mesenchyme cells (SMCs) through both cell-autonomous and non-autonomous means. Like SpKrl, HpKrl was activated in both micromere and macromere progenies. To examine the functions of HpKrl in each blastomere, we constructed chimeric embryos composed of blastomeres from control and morpholino-mediated HpKrl-knockdown embryos and analyzed the phenotypes of the chimeras. Micromere-swapping experiments showed that HpKrl is not involved in micromere specification, while micromere-deprivation assays indicated that macromeres require HpKrl for cell-autonomous specification. Transplantation of normal micromeres into a micromere-less host with morpholino revealed that macromeres are able to receive at least some micromere signals regardless of HpKrl function. From these observations, we propose that two distinct pathways of endomesoderm formation exist in macromeres, a Krl-dependent pathway and a Krl-independent pathway. The Krl-independent pathway may correspond to the Delta/Notch signaling pathway via GataE and Gcm. We suggest that Krl may be a downstream component of nuclear beta-catenin required by macromeres for formation of more vegetal tissues, not as a member of the Delta/Notch pathway, but as a parallel effector of the signaling (Krl-dependent pathway).
authors.affiliation: Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Yamazaki
authors.forename: Rika
authors.initials: R
authors.lastname: Kawabata
authors.forename: Kosuke
authors.initials: K
authors.lastname: Shiomi
authors.forename: Jun
authors.initials: J
authors.lastname: Tsuchimoto
authors.forename: Masato
authors.initials: M
authors.lastname: Kiyomoto
authors.forename: Shonan
authors.initials: S
authors.lastname: Amemiya
authors.forename: Masaaki
authors.initials: M
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004625:Embryo, Nonmammalian / Q000502:physiology*; D017403:In Situ Hybridization; D051741:Kruppel-Like Transcription Factors / Q000235:genetics*; D007814:Larva / Q000502:physiology; D008648:Mesoderm / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012617:Sea Urchins / Q000196:embryology* / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D018076:DNA, Complementary; D051741:Kruppel-Like Transcription Factors; D012333:RNA, Messenger