“Our real teacher has been and still is the embryo, who is, incidentally, the only teacher who is always right.” - Dr. Viktor Hamburger
Goals: 1. Determine how two populations of stem cells cooperatively migrate and differentiate into sensory neurons in vivo. 2. Quantitatively compare neural crest stem cell and neural crest-derived cancer migration in vivo to uncover new druggable targets for inhibiting metastasis. 3. Understand how olfactory neuronal turnover is initiated and maintained throughout adulthood.
Overview: We apply high-resolution live imaging of vertebrate model organisms to quantitatively study embryonic development and pediatric cancer, with a focus on how neural crest stem cells migrate long distances (akin to cancer metastasis) and differentiate into a variety of specialized cell types. Our entirely in vivo, system-wide approach is inspired by important, challenging long-term goals of biomedical research, namely to prevent and/or repair human birth defects and pediatric cancer progression. To achieve these goals, we must first understand how vertebrate embryonic development goes awry, which, in turn, requires understanding how development occurs correctly in its natural, in vivo environment. Therefore, we are elucidating the multicellular dynamics and fate determination underpinning stem cell migration and differentiation into neurons, including remarkable similarities to cancer cell migration and remission.We take advantage of easily accessed and manipulated neural crest migratory streams, the developing olfactory system, and the surrounding neural crest-derived mesenchyme in zebrafish as our combined experimental canvas, with the use of other model organisms as needed. Much of our work is highly interdisciplinary and benefits from synergistic interactions with several research groups (list of collaborators below). Details: By revealing the origins of vertebrate sensory neurons and the molecular and cellular processes driving the remarkable transformation from stem cell to neuron, we can better comprehend general mechanisms of neurogenesis and the potential for regeneration. Olfactory sensory neurons are particularly unique in their regenerative capacity throughout adulthood, with a completely new set of neurons present in the human nose every month. Thus, there is significant translational value in understanding the origins and differentiation pathways of these unusual derivatives.
The neural crest is a highly migratory, multipotent stem cell population that contributes to a variety of tissues in the developing embryo - including a significant portion of the peripheral nervous system - and is critically important for craniofacial development as a whole. In addition, neural crest-derived cells can give rise to neuroblastoma, the most common type of cancer in the first year of human life. Intriguingly, neuroblastoma shares many common features - both genetic and phenotypic - with the neural crest, and over 60% of neuroblastomas metastasize, with behavior reminiscent of neural crest migration.
Our previous work has revealed a novel contribution of the cranial neural crest to olfactory sensory neurons (an unexpected fate as opposed to the expected formation of craniofacial mesenchyme) via dynamic, precisely orchestrated cell migration and differentiation (Saxena et al., eLife 2013). Now, we are working to further uncover the molecular, cellular, and system-wide changes underlying this intricate developmental process, including how two tightly intermingled populations (neural crest- and placode-derived) communicate and assemble during olfactory organogenesis and what role is played in olfactory development by the surrounding neural crest-derived mesenchymal nasal cavity. Additionally, we have crossed multiple transgenic lines into the pigmentation-deficient Casper background. This setup permits live imaging and precise, two-photon laser-based perturbation of stem cell movement/differentiation in juveniles and adults. Inflicting injury and tracking recovery via live imaging allows for an in-depth look at regeneration. We are examining where stem cells reside, how they reenter the cell cycle and migrate to form neurons and mesenchymal derivatives, and which molecular pathways are conserved in adult regeneration vis-à-vis embryonic development. We are also using these tools to shed light on the understudied field of in vivo metastatic migration with the goal of discovering new inhibitors of cancer metastasis. Given the poor clinical prognosis post-metastasis, inhibiting migration and thus restricting malignant cells to their point of origin may prove highly effective at improving patient outcomes.
Neural crest and placodal progenitor cells communicate actively with their craniofacial surroundings to cooperatively guide olfactory development. Therefore, rather than study cells in vitro where context is missing, our approach makes use of live vertebrates to yield a system-wide overview of frontonasal development, i.e. how cells and signaling molecules interact with and influence each other over space and time. These data are compiled using molecular, genetic, and physical (laser-induced) perturbation combined with high-resolution imaging and downstream quantitative analysis. Our imaging toolkit includes the regular use of confocal, light sheet, and lattice light sheet (LLS) microscopy. LLS, a novel derivative of Bessel plane SR-SIM developed by Dr. Eric Betzig's group at HHMI Janelia Research Campus, has a core advantage of obtaining multiple scales and types of data - e.g., cell-cell interactions, subcellular localization, and cytoskeletal dynamics - while maintaining developmental fidelity, and its high resolution in all four dimensions allows for accurate tracking, segmentation, and analysis of multicellular behavior (see Videos for examples).By studying developmental, regenerative, and cancer biology completely in vivo, we aim to uncover insights into how neurons are formed, how complex neuronal networks are assembled and maintained, and how neural crest migration and cancer metastasis are commonly regulated.