Sequencing and analysis of the gastrula transcriptome of the brittle star Ophiocoma wendtii

Background The gastrula stage represents the point in development at which the three primary germ layers diverge. At this point the gene regulatory networks that specify the germ layers are established and the genes that define the differentiated states of the tissues have begun to be activated. These networks have been well-characterized in sea urchins, but not in other echinoderms. Embryos of the brittle star Ophiocoma wendtii share a number of developmental features with sea urchin embryos, including the ingression of mesenchyme cells that give rise to an embryonic skeleton. Notable differences are that no micromeres are formed during cleavage divisions and no pigment cells are formed during development to the pluteus larval stage. More subtle changes in timing of developmental events also occur. To explore the molecular basis for the similarities and differences between these two echinoderms, we have sequenced and characterized the gastrula transcriptome of O. wendtii. Methods Development of Ophiocoma wendtii embryos was characterized and RNA was isolated from the gastrula stage. A transcriptome data base was generated from this RNA and was analyzed using a variety of methods to identify transcripts expressed and to compare those transcripts to those expressed at the gastrula stage in other organisms. Results Using existing databases, we identified brittle star transcripts that correspond to 3,385 genes, including 1,863 genes shared with the sea urchin Strongylocentrotus purpuratus gastrula transcriptome. We characterized the functional classes of genes present in the transcriptome and compared them to those found in this sea urchin. We then examined those members of the germ-layer specific gene regulatory networks (GRNs) of S. purpuratus that are expressed in the O. wendtii gastrula. Our results indicate that there is a shared ‘genetic toolkit’ central to the echinoderm gastrula, a key stage in embryonic development, though there are also differences that reflect changes in developmental processes. Conclusions The brittle star expresses genes representing all functional classes at the gastrula stage. Brittle stars and sea urchins have comparable numbers of each class of genes and share many of the genes expressed at gastrulation. Examination of the brittle star genes in which sea urchin orthologs are utilized in germ layer specification reveals a relatively higher level of conservation of key regulatory components compared to the overall transcriptome. We also identify genes that were either lost or whose temporal expression has diverged from that of sea urchins

To Act or Not to Act, That Is the Question? Barriers and Facilitators of Bystander Intervention

A promising line of inquiry in sexual violence prevention involves training potential bystanders to intervene in situations where there is risk for violence. Theories of bystander intervention often discuss barriers to helping behavior, but there has been little empirical inquiry into this question. We will present findings of a study of both barriers and facilitators of helping behavior in the context of sexual violence among first-semester college students. Two hundred and forty-two first year college students completed surveys during their first year of college. Measures included assessment of bystander behavior, perceived barriers to helping, as well as a variety of other variables identified in the literature as key correlates of helping. Quantitative and qualitative analyses were used to (a) describe barriers and facilitators of helping, (b) examine the relationship between barriers and self-reports of helping, and (c) model individual differences in helping behavior. In quantitative analyses, barriers, as assessed in this study, were better predictors of helping behavior directed at strangers than helping of friends. Results suggested that open-ended responses about the facilitators and barriers to helping for sexual violence map well onto social-psychological models of bystander behavior, and that greater prosocial tendencies, an intrapersonal variable, increase actual helping behavior. A more specific understanding of what promotes and hinders helping can be used to enhance prevention education efforts focused on increasing helpful bystander actions