Larval arm resorption proceeds concomitantly with programmed cell death during metamorphosis of the sea urchin Hemicentrotus pulcherrimus

Abstract

Sea urchins are excellent models to elucidate metamorphic phenomena of echinoderms. However, little attention has been paid to the way that their organ resorption is accomplished by programmed cell death (PCD) and related cellular processes. We have used cytohistochemistry and transmission electron microscopy to study arm resorption in competent larvae of metamorphosing sea urchins, Hemicentrotus pulcherrimus, induced to metamorphose by L-glutamine treatment. The results show that: (1) columnar epithelial cells, which are constituents of the ciliary band, undergo PCD in an overlapping fashion with apoptosis and autophagic cell death; (2) squamous epithelial cells, which are distributed between the two arrays of the ciliary band, display a type of PCD distinct from that of columnar epithelial cells, i.e., a cytoplasmic type of non-lysosomal vacuolated cell death; (3) epithelial integrity is preserved even when PCD occurs in constituent cells of the epithelium; (4) secondary mesenchyme cells, probably blastocoelar cells, contribute to the elimination of dying epithelial cells; (5) nerve cells have a delayed initiation of PCD. Taken together, our data indicate that arm resorption in sea urchins proceeds concomitantly with various types of PCD followed by heterophagic elimination, but that epithelial organization is preserved during metamorphosis.

Environmentally relevant cadmium concentrations affect development and induce apoptosis of Paracentrotus lividus larvae cultured in vitro

“…Bar=100 μm feeding behavior which has been shown to be necessary for adult rudiment growth (Yazaki 2002). It is known that sea urchin embryos and larvae can activate physiological mechanisms of programmed cell death at specific developmental stages (Roccheri et al 2002;Sato et al 2006;Vega Thurber and Epel 2007), but an increase of apoptotic processes was observed in response to the accumulation of cadmium in embryos (Agnello et al 2006(Agnello et al , 2007 and larvae (present work). Apoptosis is supposed to be a way of removing cells whose DNA has been heavily damaged by cadmium, as documented in the case of a vertebrate model system (Hamada et al 1997).…”

Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus(Echinodermata: Echinoidea)

“…The major morphological changes that occur during the transition are the resorption of larval tissues, most noticeably the larval arms, and the extrusion and elaboration of the pre-formed juvenile structures, such as the tube feet, which grasp the substrate. In parallel, the larval arms undergo both apoptotic and autophagic cell death [15], and are accompanied by diverse physiological, metabolic and developmental changes (see [16-19] for general description of this process).…”

Effects of dietary microalgae on growth, survival and fatty acid composition of sea urchin Paracentrotus lividus throughout larval development

“…Moreover, programmed cell death (PCD) process was identified in the sea urchin Hemicentrotus pulcherrimus arms concomitantly with metamorphosis (Sato et al, 2006). It seems possible,…”