title: Larval mesenchyme cell specification in the primitive echinoid occurs independently of the double-negative gate.
abstract: Echinoids (sea urchins) are divided into two major groups - cidaroids (a 'primitive' group) and euechinoids (a 'derived' group). The cidaroids are a promising model species for understanding the ancestral developmental mechanisms in echinoids, but little is known about the molecular mechanisms of cidaroid development. In euechinoids, skeletogenic mesenchyme cell specification is regulated by the double-negative gate (DNG), in which hesC represses the transcription of the downstream mesenchyme specification genes (alx1, tbr and ets1), thereby defining the prospective mesenchyme region. To estimate the ancestral mechanism of larval mesenchyme cell specification in echinoids, the expression patterns and roles of mesenchyme specification genes in the cidaroid Prionocidaris baculosa were examined. The present study reveals that the expression pattern and function of hesC in P. baculosa were inconsistent with the DNG model, suggesting that the euechinoid-type DNG is not utilized during cidaroid mesenchyme specification. In contrast with hesC, the expression patterns and functions of alx1, tbr and ets1 were similar between P. baculosa and euechinoids. Based on these results, we propose that the roles of alx1, tbr and ets1 in mesenchyme specification were established in the common ancestor of echinoids, and that the DNG system was acquired in the euechinoid lineage after divergence from the cidaroid ancestor. The evolutionary timing of the establishment of the DNG suggests that the DNG was originally related to micromere and/or primary mesenchyme cell formation but not to skeletogenic cell differentiation.
authors.affiliation: Research Center for Marine Biology, Graduate School of Life Sciences, Tohoku University, 9 Sakamoto, Asamushi, Aomori, Aomori 039-3501, Japan yama0205@gmail.com.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Yamazaki
authors.affiliation: Department of Pharmacy, Faculty of Pharmaceutical Sciences, Aomori University, 2-3-1 Kobata, Aomori, Aomori 030-0943, Japan.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Kidachi
authors.affiliation: Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Research Center for Marine Biology, Graduate School of Life Sciences, Tohoku University, 9 Sakamoto, Asamushi, Aomori, Aomori 039-3501, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Minokawa
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002070:Butadienes; D002454:Cell Differentiation / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D017403:In Situ Hybridization; D007814:Larva / Q000502:physiology; D008648:Mesoderm / Q000502:physiology*; D008969:Molecular Sequence Data; D060172:Morpholinos / Q000235:genetics; D009570:Nitriles; D016133:Polymerase Chain Reaction; D012617:Sea Urchins / Q000254:growth & development*; D017422:Sequence Analysis, DNA
chemical_list: D002070:Butadienes; D060172:Morpholinos; D009570:Nitriles; C113580:U 0126
keywords: Cidaroid; Echinoderm; Evolution; Mesoderm; Prionocidaris baculosa; Sea urchin