GSK3 and lamellipodial dynamics in migrating neural crest cells

Cell movement is extremely important during development of the human body and during every day biological processes. In addition, cell movements become critically necessary during wound healing and when replacing aging tissues. Finally, cell movements influence how far cancer cells can spread in the body. This is a process that is very difficult to study because it is hard to see inside the live body as cells move around. In this proposal, we use an embryonic cell population called the neural crest to study how cells receive and interpret signals from the environment.

The neural crest is a very interesting cell population which contributes to all kinds of tissues in humans, including bones of the head, nerves, pigmentation and fat. Although these cells become very different, they are all born in the embryo at the edge of the neural plate. They then have to emerge from the neural tube and migrate through the body, in some cases travelling great distances before settling down. For example, the nerves that control bowel movements must travel to the gut, while correctly becoming nerves. When this goes wrong, the bowels don't work, resulting in Hirschsprung's disease. Because neural crest cells travel throughout the body before they differentiate, they are one of the few normal cell populations that are most similar to metastatic tumour cells. In fact, the neural crest cells sometimes reactivate in later life, and can then form highly invasive cancers such as melanoma, neuroblastoma and glioblastoma.

In this project, we are studying the machinery that drives the movement of these cells. We have identified several proteins help the cells to move in a forward direction, but making a broad "footlike" structure that feels its way through surrounding tissues. We want to ask what happens when these proteins are unable to function. Questions include: can the cells reach out and move in the correct direction, can they compensate by using another method of transportation, can they still move as quickly? The answers to these questions will be important for our understanding of how the tissues in the embryo come together and make organs. We will also learn what happens when the process goes wrong (for example, does this cause birth defects) as well as giving us insight into how cancer cells move through the body.

We use the neural crest as a model migratory cell population to provide fundamental insights into higher-level biological problems including wound healing, stem cell mobilization, and metastasis. Neural crest cells are multipotent embryonic cells which give rise to diverse tissues including melanocytes, craniofacial skeleton and peripheral nervous system. During embryogenesis the neural crest cells delaminate from the neural tube, undergo an epithelial to mesenchymal transition (EMT), and migrate to populate distant organs. Thus, neural crest cells are uniquely suited to the study of cell motility and invasion. Our data suggest that glycogen synthase kinase-3 (GSK-3) controls cytoskeletal reorganization and cell motility during migration to target tissues. GSK-3 is a favourite pharmacological target in the treatment of diverse disorders such as cancer metastasis, diabetes, depression and neurodegeneration; thus, a better understanding of the distinct functional requirements of GSK-3 will have broad implications. In this project we propose a novel signal transduction pathway in which GSK3 regulates the actin cytoskeleton via phosphorylation of Lamellipodin, thereby controlling neural crest cell migration. To address this, we combine live imaging and genetic mutants to follow migrating neural crest cells in their native 3D environment. Furthermore, we use molecular and biochemical approaches to unravel the potential role of GSK3 in phosphorylation of lamellipodin and thus control of cytoskeletal dynamics at the leading edge of migrating cells.

Because of the importance of cell movements in development and disease, this proposal will impact a number of areas of basic biology. Our data will also shed new light on neural crest cells which are a specially multipotent cell population, with potential for regeneration. In addition, our project will generate a large data set covering cellular changes in embryonic head development: this will be really useful for clinical geneticists as we identify more candidate disease genes. Finally, glycogen synthase kinase 3 (GSK3) may be controlled by anaplastic lymphoma kinase (ALK); both are important pharmaceutical targets. A better understanding of ALK and GSK-3 roles in in the control of lamellipodia and cell motility will be important in wound healing, neural development, skull development and cancer metastasis.

Our work is likely to have great impact for society:

These benefits are indirect; however, by increasing the genetic information available to biological scientists, we will accelerate our understanding of human development and disease. For example, our data will be immediately available for use in studying important disease processes such as congenital cranial anomalies, plasticity of neural crest stem cells, and migratory cues. Therefore, these studies may have long term global health and economic impacts.

Our work may also have direct medical implications:

Neural crest cells contribute to multiple tissue types in the body. These cells display incredible plasticity, giving rise to diverse tissues ranging from bone and cartilage to adipocytes and neurons. As a result, abnormalities in neural crest development lead to diverse congenital anomalies such as cleft palate, and Hirschsprung's Disease, where enteric innervation of the bowel is missing. Moreover, neural crest derivatives often reactivate during post-natal life, leading to highly invasive tumours such as neuroblastomas and melanomas. Even so, comparatively little is known about the genes important in differentiation of the neural crest. In particular, very little is known about the genetic requirements for migration of the neural crest, especially in mammals. Our project will document the cell behaviour of migrating neural crest cells, identify genetic requirements for GSK-3 and lamellipodin in head development and shed light on molecular control during cell migration. This is the one of the few mammalian systems where cell migration can be studied in the native three-dimensional environment.

In addition, because GSK-3 affects multiple signaling pathways, this project will also provide a wealth of data on intersecting pathways, including those that regulate cell cycle, cytoskeleton and signalling. These data may be useful for understanding neural development, skull and jaw malformations, bone development and regenerative medicine.

An additional aspect of our research is the production of several large datasets documenting the cellular changes at several stages of embryonic head development. The impact of these data will likely be extensive. As mentioned above, the identification of new candidate genes and signals important in congenital anomalies will aid clinicians, geneticists and patient groups, especially as our knowledge of human genetic variations increases exponentially.

The data from this project will be immediately useful. We will present our data at international conferences and we will rapidly publish, in peer-reviewed journals, any data generated. Any tools generated will be available to the academic community for dissemination as well as adaptation for broader uses.