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Juvenile growth of the tropical sea urchin Lytechinus variegatus exposed to near-future ocean acidification scenarios.

ABSTRACT: To evaluate the effect of elevated pCO(2) exposure on the juvenile growth of the sea urchin Lytechinus variegatus, we reared individuals for three months in one of three target pCO(2) levels: ambient seawater (380 µatm) and two scenarios that are projected to occur by the middle (560 µatm) and end (800 µatm) of this century. At the end of 89 days, urchins reared at ambient pCO(2) weighed 12% more than those reared at 560 µatm and 28% more than those reared at 800 µatm. Skeletons were analyzed using scanning electron miscroscopy, revealing degradation of spines in urchins reared at elevated pCO(2) (800 µatm). Our results indicate that elevated pCO(2) levels projected to occur this century may adversely affect the development of juvenile sea urchins. Acidification-induced changes to juvenile urchin development would likely impair performance and functioning of juvenile stages with implications for adult populations.

SUBMITTER: Albright R

PROVIDER: S-EPMC3401588 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Juvenile growth of the tropical sea urchin Lytechinus variegatus exposed to near-future ocean acidification scenarios.

Albright Rebecca R Bland Charnelle C Gillette Phillip P Serafy Joseph E JE Langdon Chris C Capo Thomas R TR

Journal of experimental marine biology and ecology 20120608

To evaluate the effect of elevated pCO(2) exposure on the juvenile growth of the sea urchin Lytechinus variegatus, we reared individuals for three months in one of three target pCO(2) levels: ambient seawater (380 µatm) and two scenarios that are projected to occur by the middle (560 µatm) and end (800 µatm) of this century. At the end of 89 days, urchins reared at ambient pCO(2) weighed 12% more than those reared at 560 µatm and 28% more than those reared at 800 µatm. Skeletons were analyzed us ...[more]

PMID: 22833691

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Project description:Using standard morphometric methods and gene expression profiling with a DNA microarray, we explored the impacts of high CO2 conditions on development of the sea urchin, Lytechinus pictus, a pelagic larvae that forms a calcium carbonate endoskeleton. Larvae were raised from fertilization to pluteus stage in seawater with elevated CO2 conditions based upon IPCC emissions scenarios B1 (540ppm CO2) and A1FI (970ppm CO2). Larval L. pictus were cultured in seawater treated with three different concentrations of CO2. We aerated water in culture chambers with air that had been mixed to different CO2 concentrations chosen from IPCC predictions of future atmospheric CO2 levels (28). The B1 scenario, one of the most optimistic, predicts a stabilization of atmospheric CO2 levels at ~540 ppm by 2100, and the A1F1 scenario, which, reflecting a more âbusiness as usualâ scenario, predicts atmospheric CO2 levels of ~970 ppm by 2100. Compressed air (~380 ppm CO2) was used as a control condition. The culture chambers were 20 L buckets medified to allow aeration bubbles of the experimental gas to mix with and gently stir the culture water without contacting the larvae. Replacement seawater (0.35 Î¼m filtered) was added at a constant rate of 0.5 L hr-1. Water pH of each chamber was monitored daily using a Radiometer Analytical PHM240 pH meter. Adult L. pictus were maintained in flowing seawater at ambient temperature (~15-18 ÂºC) and fed kelp until use. Spawning was induced by coelomic injection of 0.5 M KCl, and eggs were collected in 0.35 Î¼m-filtered seawater. Eggs from 5 females were combined in approximately equal concentrations. Sperm from a single male was collected in the same way, diluted with filtered seawater and added to the egg mixture; thus, all the larvae are half-siblings. Immediately following fertilization, embryos were split into 12 culture chambers providing four replicates of the three CO2 treatments. At the 48 hour time point, a sample of 40,000 larvae was removed from each of the 8 cultures in the 380 and 970 ppm treatments and stored in1 mL Trizol at -80 ÂºC for later RNA analysis. The larval cDNA samples from each treatment were competitively hybridized on each microarray following a balanced incomplete block design (BIBD) with respect to the assignment of treatments to arrays. In this way, differential expression between all pairs of treatments is estimated with equal precision. Although dye swaps of technical replicates were not used, treatment and dye effects are orthogonal to one another, i.e. treatment effects can be estimated independently of dye effects.

Project description:BackgroundGastrulation is a complex orchestration of movements by cells that are specified early in development. Until now, classical convergent extension was considered to be the main contributor to sea urchin archenteron extension, and the relative contributions of cell divisions were unknown. Active migration of cells along the axis of extension was also not considered as a major factor in invagination.ResultsCell transplantations plus live imaging were used to examine endoderm cell morphogenesis during gastrulation at high-resolution in the optically clear sea urchin embryo. The invagination sequence was imaged throughout gastrulation. One of the eight macromeres was replaced by a fluorescently labeled macromere at the 32 cell stage. At gastrulation those patches of fluorescent endoderm cell progeny initially about 4 cells wide, released a column of cells about 2 cells wide early in gastrulation and then often this column narrowed to one cell wide by the end of archenteron lengthening. The primary movement of the column of cells was in the direction of elongation of the archenteron with the narrowing (convergence) occurring as one of the two cells moved ahead of its neighbor. As the column narrowed, the labeled endoderm cells generally remained as a contiguous population of cells, rarely separated by intrusion of a lateral unlabeled cell. This longitudinal cell migration mechanism was assessed quantitatively and accounted for almost 90% of the elongation process. Much of the extension was the contribution of Veg2 endoderm with a minor contribution late in gastrulation by Veg1 endoderm cells. We also analyzed the contribution of cell divisions to elongation. Endoderm cells in Lytechinus variagatus were determined to go through approximately one cell doubling during gastrulation. That doubling occurs without a net increase in cell mass, but the question remained as to whether oriented divisions might contribute to archenteron elongation. We learned that indeed there was a biased orientation of cell divisions along the plane of archenteron elongation, but when the impact of that bias was analyzed quantitatively, it contributed a maximum 15% to the total elongation of the gut.ConclusionsThe major driver of archenteron elongation in the sea urchin, Lytechinus variagatus, is directed movement of Veg2 endoderm cells as a narrowing column along the plane of elongation. The narrowing occurs as cells in the column converge as they migrate, so that the combination of migration and the angular convergence provide the major component of the lengthening. A minor contributor to elongation is oriented cell divisions that contribute to the lengthening but no more than about 15%.

Project description:BackgroundThe sea urchin is a basal deuterostome that is more closely related to vertebrates than many organisms traditionally used to study neurogenesis. This phylogenetic position means that the sea urchin can provide insights into the evolution of the nervous system by helping resolve which developmental processes are deuterostome innovations, which are innovations in other clades, and which are ancestral. However, the nervous system of echinoderms is one of the least understood of all major metazoan phyla. To gain insights into echinoderm neurogenesis, spatial and temporal gene expression data are essential. Then, functional data will enable the building of a detailed gene regulatory network for neurogenesis in the sea urchin that can be compared across metazoans to resolve questions about how nervous systems evolved.ResultsHere, we analyze spatiotemporal gene expression during sea urchin neurogenesis for genes that have been shown to be neurogenic in one or more species. We report the expression of 21 genes expressed in areas of neurogenesis in the sea urchin embryo from blastula stage (just before neural progenitors begin their specification sequence) through pluteus larval stage (when much of the nervous system has been patterned). Among those 21 gene expression patterns, we report expression of 11 transcription factors and 2 axon guidance genes, each expressed in discrete domains in the neuroectoderm or in the endoderm. Most of these genes are expressed in and around the ciliary band. Some including the transcription factors Lv-mbx, Lv-dmrt, Lv-islet, and Lv-atbf1, the nuclear protein Lv-prohibitin, and the guidance molecule Lv-semaa are expressed in the endoderm where they are presumably involved in neurogenesis in the gut.ConclusionsThis study builds a foundation to study how neurons are specified and evolved by analyzing spatial and temporal gene expression during neurogenesis in a basal deuterostome. With these expression patterns, we will be able to understand what genes are required for neural development in the sea urchin. These data can be used as a starting point to (1) build a spatial gene regulatory network for sea urchin neurogenesis, (2) identify how subtypes of neurons are specified, (3) perform comparative studies with the sea urchin, protostome, and vertebrate organisms.

Dataset Information

Juvenile growth of the tropical sea urchin Lytechinus variegatus exposed to near-future ocean acidification scenarios.

Publications

Juvenile growth of the tropical sea urchin Lytechinus variegatus exposed to near-future ocean acidification scenarios.

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