Phagocytes must clear cellular debris created by developmental events or injury to maintain tissue homeostasis. Massive amounts of cellular debris are created during development of the nervous system. Neuronal debris can be created by the death of entire cells through apoptosis or the selective pruning of neurites through regulated degeneration. The cellular and genetic mechanisms used to recognize and dispose of neuronal debris are not fully understood. In many cases blood-derived professional phagocytes clear neuronal debris; however, it is increasingly appreciated that certain non-professional phagocytic cell types play a major role in nervous system homeostasis. For example, I recently showed using live imaging and genetics in larval zebrafish that vertebrate epidermal cells are the primary phagocyte that clears somatosensory peripheral axon debris. Failure to maintain somatosensory peripheral axons leads to peripheral neuropathies, which are associated with several common human diseases. The experiments proposed in this application will use a combination of cellular, genetic, and computational approaches to further develop the zebrafish epidermis as the premier in vivo model to study clearance of neuronal debris by non-professional phagocytes. I hypothesize that phagocytosis of neuronal debris by the epidermis is critical for two important developmental events. First, widespread apoptosis occurs during neural tube morphogenesis, but the phagocyte responsible for eating this debris has not been identified.
In Aim 1, I will test if the epidermal ectoderm eats neuronal debris during neural tube closure. In collaboration with physicist Dr. Katsushi Arisaka, I will learn how to build and operat a light-sheet microscope, which I will use to image these events with high-temporal resolution across a large swath of the zebrafish embryo. Second, somatosensory neurons undergo significant remodeling during juvenile development.
In Aim 2, I will test if the epidermis clears somatosensory axon debris in juveniles by using a combination of genetics and a novel injury model I developed to live image debris clearance at these later stages.
In Aim 3, I will identify the phagocytic pathways used by the epidermis to recognize neuronal debris through a combination of hypothesis- and discovery-based approaches. In the course of this aim, I will collaborate with computational biologist Dr. Matteo Pellegrini to further strengthen my computational skills in the analysis of large genomic data sets. In addition to these research opportunities, this development award will provide me with critical career training in laboratory leadership and scientific communication. I will use the excellent career development resources available at UCLA to prepare for my goal of starting an independent lab. My co-mentors Drs. Alvaro Sagasti and Luisa Iruela-Arispe will provide critical mentorship training before, during, and after my transition to independence. Together the training facilitated by this award will pave the way for my future research goal of understanding how clearance of neuronal debris by the epidermis regulates nervous system morphogenesis and homeostasis.
Neuronal debris created by apoptotic or degenerative mechanisms during development of the nervous system must be cleared to maintain nervous system homeostasis. I have recently found that vertebrate epidermal cells clear neuronal debris and, in this proposal, I aim to understand the cellular and molecular mechanisms involved. These studies will have implications for several important human diseases, including neural tube defects and peripheral neuropathies.
|Rasmussen, Jeffrey P; Vo, Nhat-Thi; Sagasti, Alvaro (2018) Fish Scales Dictate the Pattern of Adult Skin Innervation and Vascularization. Dev Cell 46:344-359.e4|