Figure 2.

Model linking trans-splicing to nutrient dependent translational control of maternal mRNA. Growth is characterized by an increase in the production of the protein synthesis machinery (via the translation of TOP mRNAs) and is limited by resource availability. The mTOR pathway mediates the response to nutrient levels by controlling the translation of TOP mRNAs. Egg number in O. dioica is dependent on nutrient levels and the majority of maternal mRNAs and TOP mRNAs are trans-spliced. We propose a model whereby the spliced-leader fulfills the function of the TOP motif and allows the translational control of trans-spliced mRNAs. This allows the animal to adjust reproductive output, and therefore population level, in accordance with dynamic resource levels (including algal blooms) in its environment. Control at the translational level allows a more rapid response to changes in nutrient levels compared to transcriptional control, and this may be of particular importance for organisms with short life cycles.