Elucidate mechanisms of nuclear size control: Interspecies nuclear scaling in Xenopus is regulated by lamin import, however it is unknown if lamins are sufficient to regulate nuclear size or if other cargos are involved. We are testing if import of individual cargos into nuclei assembled in Xenopus egg extract is sufficient to control nuclear size. Nuclear import also contributes to changes in nuclear size during early Xenopus development, however import mechanisms do not fully account for the over five-fold reduction in nuclear envelope (NE) surface area from the fertilized one-cell embryo to the gastrula. Extracts from different stage embryos are being used to assess how changes in nuclear export activity and nuclear membrane structure and composition contribute to developmental nuclear scaling.
Investigate how nuclear size impacts development and cell function: The concentrations of two transport factors, importin a and Ntf2, are sufficient to account for interspecies nuclear scaling in Xenopus. Both factors modulate the rate of lamin import, with importin a increasing overall import rates and Ntf2 reducing import based on cargo size. It is unknown if these same factors regulate nuclear size in other systems. We are addressing this question in cultured mammalian cells where the levels and activities of nuclear scaling factors can be altered and effects on nuclear size can be quantified. The effects of nuclear size on cell function have been difficult to study because mechanisms of nuclear size regulation were largely unknown. With a handle on some of the factors that control nuclear size, we are investigating how altering nuclear size affects developmental timing and patterning in Xenopus embryos and cell size, proliferation, and invasive potential in tissue culture.
Investigate how nuclear size affects subnuclear organization: Nuclear size is thought to regulate the three-dimensional organization of chromatin and the association of specific gene regions with the NE. In turn, this organization can influence gene expression patterns. To investigate this idea, we are utilizing new techniques for measuring changes in global chromatin conformations and gene expression profiles.