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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.11.035 Byline: Atsuko Yamazaki (a), Rika Kawabata (a), Kosuke Shiomi (a), Jun Tsuchimoto (a), Masato Kiyomoto (b), Shonan Amemiya (c), Masaaki Yamaguchi (a) Keywords: Kruppel-like; Mesoderm specification; Delta/Notch signaling; Effector; 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). Author Affiliation: (a) Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan (b) Tateyama Marine Laboratory, Marine and Coastal Research Center, Ochanomizu University, Kou-yatsu, Tateyama 294-0301, Japan (c) Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Misaki, Miura 238-0225, Japan Article History: Received 22 June 2007; Revised 6 November 2007; Accepted 20 November 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.12.038 Byline: Hiroaki Nakano (a)(b)(c), Naoyuki Murabe (a), Shonan Amemiya (b), Yoko Nakajima (a) Keywords: Larval nervous system; Auricularia; Doliolaria; Pentacutula; Apical ganglia; Development; Metamorphosis; Sea cucumber; Echinoderm Abstract: The nervous system development of the sea cucumber Stichopus japonicus was investigated to explore the development of the bilateral larval nervous system into the pentaradial adult form typical of echinoderms. The first nerve cells were detected in the apical region of epidermis in the late gastrula. In the auricularia larvae, nerve tracts were seen along the ciliary band. There was a pair of bilateral apical ganglia consisted of serotonergic nerve cells lined along the ciliary bands. During the transition to the doliolaria larvae, the nerve tracts rearranged together with the ciliary bands, but they were not segmented and remained continuous. The doliolaria larvae possessed nerves along the ciliary rings but strongly retained the features of auricularia larvae nerve pattern. The adult nervous system began to develop inside the doliolaria larvae before the larval nervous system disappears. None of the larval nervous system was observed to be incorporated into the adult nervous system with immunohistochemistry. Since S. japonicus are known to possess an ancestral mode of development for echinoderms, these results suggest that the larval nervous system and the adult nervous system were probably formed independently in the last common ancestor of echinoderms. Author Affiliation: (a) Department of Biology, Keio University, Yokohama 223-8521, Japan (b) Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, FSB-501, Kashiwa, Chiba 277-8562, Japan (c) Kristineberg Marine Research Station, SE 450 34, Fiskebackskil, Sweden Article History: Received 21 July 2005; Revised 3 November 2005; Accepted 14 December 2005

Coelomogenesis in the isocrinid sea lily, Metacrinus rotundus, is described through the swimming larval stages. After the late gastrula stage, the archenteron separates from the ectoderm to form an archenteral sac, which develops into a dumbbell shape consisting of anterior and posterior lobes, and a middle part connecting both lobes. The anterior and posterior lobes, and the middle part, become separated into an axo‐hydrocoel, the left and right somatocoels and an enteric sac, respectively. The hydrocoel forms from the left lower edge of the axo‐hydrocoel and becomes separated from the axocoel by the late dipleurula stage, when chambered organs and coelom X bud off from the anterior tip of the right and left somatocoels, respectively. Coelom X does not occur in comatulid crinoids (feather stars), and its fate is unclear. The pore canal extends from the axocoel. The hydrocoel differentiates into a crescent shape at the overtime semidoliolaria stage, a few days after the semidoliolaria becomes competent to settle. Coelomogenesis in M. rotundus is much simpler than in the comatulids and probably represents the ancestral mode of the crinoids. As each portion of the dumbbell sac differentiates almost in situ into each coelom, presumptive fates in the sac are easily followed in M. rotundus. [ABSTRACT FROM AUTHOR]

The early stalked stages of an isocrinid sea lily, Metacrinus rotundus, were examined up to the early pentacrinoid stage. Larvae induced to settle on bivalve shells and cultured in the laboratory developed into late cystideans. Three-dimensional (3D) images reconstructed from very early to middle cystideans indicated that 15 radial podia composed of five triplets form synchronously from the crescent-shaped hydrocoel. The orientation of the hydrocoel indicated that the settled postlarvae lean posteriorly. In very early cystideans, the orals, radials, basals and infrabasals, with five plates each in the crown, about five columnals in the stalk, and five terminal stem plates in the attachment disc, had already formed. In mid-cystideans, an anal plate appeared in the crown. Late cystideans cultured in the field developed into pentacrinoids about 5 months after settlement. These pentacrinoids shared many crown structures with adult sea lilies. On the other hand, many features of the stalk differed from those in adult isocrinids, while sharing many characteristics with the stalk of feather star pentacrinoids, including disc-like proximal columnals, high and slender median columnals, synarthrial articulations developmentally derived from the symplexial articulations, limited formation of cirri only in the proximal columnal(s), and an attachment disc. On the basis of these findings, phylogenetic relationships among extant crinoid orders are discussed. [ABSTRACT FROM AUTHOR]

Sea lilies or stalked crinoids are capable of regenerating not only all their arms but also their crowns. Experiments with the species Metacrinus rotundus provide the first evidence that autotomy, or the voluntary detachment and subsequent regrowth of a body part, does occur among sea lilies. Moreover, the upper most region of the sea-lily stalk including the basal plates is able to regrow the entire crown. Food and materials from the stalk, particularly the upper five centimeters, are used to regenerate the crown.

Embryos and larvae of an isocrinid sea lily, Metacrinus rotundus, are described by scanning electron microscopy. Around hatching (35 h after fertilization), the outer surface of the gastrula becomes ubiquitously covered with short cilia. At 40 h, the hatched swimming embryo develops a cilia-free zone of ectoderm on the ventral side. By 3 days, the very early dipleurula larva develops a cilia-free zone ventrally, densely ciliated regions laterally, and a sparsely ciliated region dorsally. At this stage, the posterior and anterior ciliary bands first appear: the former runs along a low ridge separating the densely from the sparsely ciliated epidermal regions, while the latter is visible, at first discontinuously, along the boundary between the densely ciliated lateral regions and the cilia-free ventral zone. In the late dipleurula larva (5 days after fertilization), the anterior and posterior loops of ciliary bands are well defined. The transition from the dipleurula to the semidoliolaria larva occurs at 6 days as the posterior loop becomes rearranged to form incompletely circumferential ciliary bands. The larva becomes competent to settle at this stage. The arrangement of the ciliary bands on the semidoliolaria is maintained during the second week of development, while the larva retains its competence to settle. The larval ciliary patterns described here are compared with those of stalkless crinoids and eleutherozoan echinoderms. The closest morphological similarities are between M. rotundus and the basal eleutherozoan class Asteroidea. [ABSTRACT FROM AUTHOR]