Investigation of mechanisms regulating cell proliferation in the zebrafish developmental program
Amin, Shivas Rajni
Doctor of Philosophy
Vertebrate development requires that cell proliferation be properly coordinated with morphogenesis, the process by which an embryo acquires form, and cell specification, the process by which unique cellular characteristics arise. My work has focused on the investigation of specific genetic networks that we have found to be involved in the regulation of cell proliferation during zebrafish (Danio rerio) development. We have identified two genes, wee1 and lmo4b, that are involved in two distinct, proliferative regulatory mechanisms during development. My work demonstrates that wee1 is required for the progression of the cell cycle after the midblastula transition (MBT). Loss of wee1 abolishes a temporally acquired G2/M checkpoint resulting in widespread cell death. We also found that the wee1-dependent G2/M checkpoint is required for a developmentally programmed deceleration of the cell cycle. In addition, my work shows that lmo4b functions in a spatial manner by restricting the expression of the neural proliferative transcription factor, six3. Loss of lmo4b results in the expansion of neural tissue at the expense of non-neural tissue through the deregulation of six3. This work highlights two cell cycle regulatory mechanisms, wee1 and lmo4b, involved in the zebrafish developmental program that are necessary for proper morphogenesis and cell specification. My analysis of wee1 indicates that temporal maintenance of the G2/M phase transition is the focal point of cell cycle regulation during gastrulation. Following gastrulation, the expression of spatially restricted genes, such as lmo4b, is required to modulate the G1/S phase transition. This research assists in the establishment of a model for cell cycle regulation during zebrafish development.