The effects of diatom oxylipin 2-trans-4-trans decadienal on gene expression during development and growth of the tunicate Ciona intestinalis

Abstract

Diatoms, a major class of unicellular photosynthetic algae, have traditionally been considered as principal components of planktonic crustacean copepod diets, enhancing their fecundity and development. This idea largely persisted until 1993 when a world-wide group of researchers reported what is now known as the diatom-copepod paradox (Ban et al, 1997). Although copepods consume diatoms to a large extent, they are not an optimal food for copepod growth, because their consumption leads to longer generation times and increased mortality rates in the offspring (Ianora et al., 2004; Poulet et al., 1994). The anti-proliferative effect of diatoms on copepod reproduction is caused by the presence of antimitotic compounds, which reduce egg viability in copepods by blocking mitotic divisions during embryogenesis (Poulet et al., 1994). These inhibitory effects are correlated to the production of polyunsaturated aldehydes (PUAs) (Miralto et al., 1999; d'Ippolito et al., 2002a; Ianora et al., 2004), which are produced by diatoms in response to physical damage as occurs during copepod grazing (Pohnert, 2000). PUAs have been demonstrated to have similar effects on benthic invertebrates such as polychaetes (Caldwell, 2005), sea urchins (Romano et al, 2010) and tunicates (Tosti et al., 2003). In these organisms PUAs induce the disruption of gametogenesis, gamete functionality, fertilization, embryonic mitosis, and larval fitness and competence (reviewed by Caldwell, 2009). The cell targets of these compounds, however, remains largely unknown. The aim of this thesis was to identify, on a large scale, the genes targeted by the diatom PUA 2-trans-4-trans-decadienal (DD) using the tunicate Ciona intestinalis. The tools, techniques and genomic resources available for Ciona, as well as the suitability of Ciona embryos for medium-to high-throughput strategies, are key to their employment as model organisms in different fields, including the investigation of toxic agents that could interfere with developmental processes. Here it is demonstrated that DD can induce developmental aberration in Ciona larvae in a dose dependent manner. Moreover, through a preliminary analysis of microarray experiments, DD is demonstrated to affect the expression level of genes involved in stress response, developmental processes and cell adhesion.