Dan Grimes (Burdine Lab)
Making and Breaking Symmetry in Development, Growth and Disease
The body plans of the vast majority of animal species are based on bilateral symmetry, with a clear left and right side. However, many of these bilaterians, and especially vertebrates, exhibit striking asymmetries between left and right in the positioning and patterning of their internal organs. In humans, for instance, the heart and stomach are positioned to the left side and the liver to the right. By contrast, the musculoskeletal system is symmetrical between left and right. In the talk, I will discuss two topics: 1) the establishment of left-right asymmetry in the embryo and 2) the maintenance of left-right symmetry in the spine during growth. A role for motile cilia and fluid flow in the first, left-right asymmetric patterning, has been long known but our work has recently linked cilia and flow to spinal symmetry as well. Finally, I will report our experiments that implicate Polycystins, large transmembrane proteins with enigmatic functions, to the generation of these symmetries and asymmetries, potentially via mechanosensory function in flow-sensing cells.
Chen Cao (Levine Lab)
A comprehensive four-dimensional single cell transcriptome analysis of a proto-vertebrate
Ascidians have served as a model for understanding the role of localized determinants and cell lineages in animal development for over 100 years. Here we present the complete transcriptomes of 36,244 cells from 9 different developmental stages of Ciona intestinalis, spanning the onset of gastrulation through late tailbud stages. This corresponds to ~4× coverage on average for every cell at every stage of development of ascidian embryogenesis. The reconstructed gene expression lineages confirm and extend classical cell lineages, and were used to determine regulatory cascades and provisional single cell gene networks for a variety of cell types, including different regions of the nervous system. These datasets strengthen the evidence that ascidians possess a number of transitional properties, including a hybrid notochord with features of both cephalochordates and vertebrates. They also provide extensive information about the development of forebrain derivatives such as the hypothalamus, and suggest a model for the evolution of the vertebrate telencephalon. The high-resolution single cell datasets can be used as a roadmap for the reconstruction of gene regulatory networks and cell lineages in vertebrates. This information should also help illuminate vertebrate cell atlas datasets by providing extensive insights into the evolutionary origins of novel cell types.