Mechanisms of Scale Invariance in Embryonic Patterning Systems

Abstract

Embryos pattern themselves with remarkable consistency and readily adjust their patterning programs to drastic changes in embryo size. This robustness of pattern formation, termed scale invariance, requires cells to determine their precise location within the organism. Recent technological advances in genetics, molecular biology, and imaging have enabled unprecedented insights into how cells send and receive patterning signals. In this dissertation, I examine how vertebrate embryos convey, interpret, and regulate positional information. In Chapter II, I use novel embryological techniques, genetic perturbations, and confocal fluorescence microscopy to explore how signaling by the morphogen Sonic Hedgehog enables scale-invariant patterning of the ventral spinal cord. We find that Sonic Hedgehog represses the positive signaling regulator Scube2 and explore its function. In addition, we demonstrate that this self-regulation of morphogen signaling is necessary for pattern scaling. In Chapter III, we uncover the gene expression of single cells during vertebrate development and map the cell state landscape of early patterning. We then focus on how cell state landscapes change when critical patterning cues are disrupted via targeted mutagenesis with CRISPR Cas9. In Appendix 3, my colleagues and I use the scale invariance of somite patterning to gain new insights into patterning mechanisms with live imaging, pharmacological interventions, and embryological manipulations. We find that Fibroblast Growth Factor signaling gradients in the presomitic mesoderm are scale-invariant and make important refinements to the existing clock and wavefront model. We then test the predictions of our mathematical model against proposed alternatives and observe “echos” in somite patterning, which are uniquely predicted by our model. Taken together, this work yields new insights into the mechanism of vertebrate patterning and provides a valuable genomic resource for the scientific community.