The role of centrosomally segregated RNAs and organizer signaling in patterning the Ilyanassa embryo

Thesis (Ph. D.)--University of Rochester. Dept. of Biology, 2012.During embryogenesis of all animals, a combination of intrinsic factors segregated via asymmetric cell division and cell-cell signaling are required for patterning the embryos. Results from fate mapping, cell ablation and transplantation experiments have shown that Ilyanassa embryo is particularly reliant on cell-autonomous cues for patterning. During early cleavages, a series of asymmetric cell division along the animal-vegetal axis produces micromere quartets with different developmental potential. Recently, a novel mechanism was discovered where RNAs are asymmetrically segregated via centrosomal localization. Different RNAs are segregated into different subsets of cells, in a quartet-specific manner, suggesting a role in patterning the early micromeres with different developmental potential. In addition to asymmetrically segregated RNAs, the main inductive signaling, coming from the 3D macromere, the organizer, is required for establishing the dorsalventral axis by inducing the neighboring dorsal and lateral cells to pursue dorsal cell fates. The results from a collection of embryological and molecular studies generated the following model for cell fate specification in the Ilyanassa embryo: at their birth, different micromere quartets inherit different subsets of centrosomal-mediated segregated RNAs, which pre-pattern the micromere quartets with different developmental potentials. These asymmetrically segregated RNAs are then differentially regulated by the organizer signaling to select for either dorsal or ventral fates. Background information for my work is discussed in Chapter 1, including the importance of asymmetric cell division and the advantages of using the Ilyanassa embryo as a model organism to study asymmetric cell division and cell fate specification. In Chapter 2, I show that Tis11, a RNA segregated to the ventral 3rd quartet, plays an important role in the normal esophagus development. Then, in Chapter 3, I discuss a screen for segregated RNAs that are regulated by the organizer signaling and required in cell fate specification. In Chapter 4, I describe the observations on the clonal contributions and behaviors of the first four quartet micromeres and the fourth quartet macromeres, at four different developmental time points. Last, I make some concluding comments on my work in Chapter 5