MOL BIO COLLOQUIUM
November 4, 2022
Characterizing the transcriptional landscape in electrically stimulated cells
Directed collective cell migration is critical in biological processes such as morphogenesis, cancer cell invasion and wound healing. Specifically, human skin generates an endogenous electrical field that is maintained and upon injury, this transepithelial potential is ‘short circuited’, initiating a current that the cells can sense and electrical fields of ~1V/cm . Cells follow this field in a process called ‘electrotaxis’. There is increasingly promising data that shows application of direct current stimulation to skin wounds can accelerate cell migration by activation of PI3K/PTEN pathway and also mediate the electrotactic response of neutrophils and dermal fibroblasts, both crucial for the healing process. Additionally, our group has shown accelerated in vitro wound closure using converging electric. Because of this potential, there is a plethora research covering the various conditions of electrotaxing cells across different parameters of electrical stimulation, types of electrodes uses and time course However, the exact molecular mechanisms and transcriptional changes that allow for this mode of migration remains elusive as there is no standardization of cells or devices in the literature. Existing research shows that electrotaxis does result in a transcriptional response; however, the exact correlation between migratory response and changes in gene expression is not unified across different stimulation parameters. Elucidating the coupling between transcriptional changes to cell migratory speed will generate an integrated atlas to understand how electrotaxis differs from other migratory responses and identify novel genes to further investigate its interaction with other signaling and metabolic pathways. Using my experimental experience and my lab’s unique expertise for electrotaxis, I plan to: (1) Characterize the biophysical changes across varying stimulation parameters and (2) Map the transcriptional landscape in electrotaxing cells.
Molecular evolution and development of the mammalian gliding membrane
Understanding how genomic changes over evolutionary time lead to phenotypic changes is a central question in evolutionary biology. While many loci responsible for evolutionary trait loss (e.g. flightlessness in birds, loss of limbs in snakes, and pelvic reduction in sticklebacks) have been identified, little is known about gene regulatory network (GRN) changes that lead to the evolution of new traits. Furthermore, the degree of molecular and genomic convergence underlying instances of convergent trait gain is unclear. To address these questions, my dissertation will focus on studying the development and evolution of the mammalian gliding membrane, or patagium, a specialized tissue that has independently evolved in multiple groups of mammals. First, using single-cell RNA and ATACseq, I will identify the cell-type specific GRNs that regulate the formation of the sugar glider patagium, and functionally test components of these GRNs using in vivo transgenic tools. Second, using a combination of comparative genomics, histology, epigenomics, and in vitro assays, I will determine whether bat lateral patagia evolved through shared or distinct molecular mechanisms. Taken together, this study will help dissect the GRNs involved in driving the development of a novel trait in sugar gliders, and help better understand how this trait has convergently evolved in different mammalian lineages.
EMILY KOLENBRANDER HO
Put a (brachyenteron) ring on it: Erk signal interpretation and pattern formation in the early embryo
How do stripes of gene expression form at particular positions in the embryo? Classically, morphogen gradients induce distinct target genes at different embryonic positions that work in combination to establish specific stripes of downstream genes. For example, the posterior gradient of Torso activity in the early Drosophila embryo produces distinct domains of two target genes – tailless (tll) and huckebein (hkb) – that are required to produce a stripe of brachyenteron (byn), a gene involved in gut specification. However, recent live imaging and optogenetic experiments have revealed mysteries about byn patterning that cannot be explained by the classic gradient model. First, byn expression is dynamic, beginning as a cap that later refines into a stripe. Second, even simple, uniform optogenetic inputs are sufficient to rescue normal development, suggesting that the Torso gradient may not be absolutely required for the formation of a byn stripe. Using precision optogenetic control over Erk signaling in live embryos, we identify differential dynamics of byn’s regulators tailless and huckebein that explain the dynamic patterns of byn expression. Further, we find that intracellular diffusion of signaling components produces gradients of Erk activity, even from all-or-none optogenetic inputs. Altogether, this work reveals that formation of the byn stripe is remarkably robust to severe disruption of the signaling gradient.