Development in all multi-cellular organisms depends on an asymmetric distribution of patterning molecules that occurs during the earliest cleavage cycles. As a consequence of the early establishment of asymmetry, cells embark on different pathways to ultimately become the recognizable organs of the adult. This proposal focuses on the role of two signaling pathways - signaling through the NMDA receptor and signaling through the NOTCH pathway - in the establishment of asymmetry and cell fate in the mud snail Ilyanassa. Preliminary findings suggest that blocking either of these pathways disrupts important events in determining the fate of particular cells and results in a failure to establish bilateral symmetry in the embryo. The Nagy lab uses Ilyanassa as their model system as their embryos undergo a series of pronounced asymmetric cell divisions and have a distinctive pattern of cell fates, characteristics that make them ideally suited for the proposed research. Significantly, the NMDA receptor is best known for its role in synaptic transmission and memory and learning and has not previously been implicated in early cell division in any animal species. The expected results will broadly impact the scientific community because asymmetric cell cleavage is a fundamental property of stem cells and increasing our understanding of stem cell behavior effects the ability of the scientific community to improve health care through treatments utilizing stem cells. The proposed work forms the basis of graduate and undergraduate training and outreach to local elementary and high schools. As these experiments are straightforward methodologically, they provide an excellent opportunity to introduce student and teachers-in training to the beauty of the invertebrate embryo and to modern methods in cell and molecular biology, imaging, and design and interpretation of scientific experiments. The lab actively participates in programs designed to recruit under-represented minorities from the local high schools and community college for research experiences.
In the most general sense, the aims of this project were to discover how the development of the mud snail is regulated, i.e., how the snail designates one part as its future head, another as its future shell. The genetic hierarchies that determine how variable parts of an organism are determined are best understood in a few model organisms like the fruit fly or the mouse. The degree to which these same genetic programs are used in the development of species throughout the animal kingdom is less well known. We took a close look at how some of the signaling pathways known to regulate cell-cell interactions and to specify whether a cell becomes a particular fate in flies and mouse function in the snail. Surprisingly, we found that serotonin, best known for its role in neuronal signaling, appears to control the position of the mitotic spindle during some of the earliest embryonic cell divisions. Disrupting serotonin signaling disrupts the asymmetry of the early cell divisions and the size of the resultant daughter cells. A role for serotonin in cell division had not been previously reported in any system. Because spindle positioning and asymmetric division play a fundamental role in stem cells and many other developmental processes, these results lay a foundation for future studies to determine the degree to which serotonin functions in regulating the mitotic spindle in other species, including humans. In addition to these scientific findings, the laboratory funded by this grant provided a supportive training environment for of high school students, undergraduates, graduate students and a postdoctoral fellow. Students were trained in hypothesis building, diverse experimental methods, data interpretation, and general principles of molecular, cellular and developmental biology.
