Biology subjects

Oakey, J.

Publications and source records attributed to Oakey, J..

3 recordsLinked to original sources

bioRxiv2019

Microtubule growth rates are sensitive to global and local changes in microtubule plus-end density

The microtubule (MT) cytoskeleton plays critically important roles in numerous cellular functions in eukaryotes, and it does so across a functionally diverse and morphologically disparate range of cell types [1]. In these roles, MT assemblies must adopt distinct morphologies and physical dimensions to perform specific functions [2-5]. As such, these macromolecular assemblies--as well as the dynamics of the individual MT polymers from which they are made--must scale and change in accordance with cell size and geometry. As first shown by Inoue using polarization microscopy, microtubules assemble to a steady state in mass, leaving enough of their subunits soluble to allow rapid growth and turnover. This suggests some negative feedback that limits the extent of assembly, for example decrease in growth rate, or increase in catastrophe rate, as the soluble subunit pool decreases. Such feedbacks might be global or local. Although these ideas have informed the field for decades, they have not been observed experimentally. Here we describe an experimental system designed to examine these long-standing ideas and determine a role for MT plus-end density in regulating MT growth rates.

molecular biology↗

bioRxiv2019

The perinuclear ER scales nuclear size independently of cell size in early embryos

SUMMARYNuclear size plays pivotal roles in gene expression, embryo development, and disease. A central hypothesis in organisms ranging from yeast to vertebrates is that nuclear size scales to cell size. This implies that nuclei may reach steady state sizes set by limiting cytoplasmic pools of size-regulating components. By monitoring nuclear dynamics in early sea urchin embryos, we found that nuclei undergo substantial growth in each interphase, reaching a maximal size prior to mitosis that declined steadily over the course of development. Manipulations of cytoplasmic volume through multiple chemical and physical means ruled out cell size as a major determinant of nuclear size and growth. Rather, our data suggest that the perinuclear endoplasmic reticulum, accumulated through dynein activity, serves as a limiting membrane pool that sets nuclear surface growth rate. Partitioning of this local pool at each cell division modulates nuclear growth kinetics and dictates size scaling throughout early development.

cell biology↗

bioRxiv2019

Cytoplasmic volume and limiting nucleoplasmin scale nuclear size during Xenopus laevis development

How nuclear size is regulated relative to cell size is a fundamental cell biological question. Reductions in both cell and nuclear sizes during Xenopus laevis embryogenesis provide a robust scaling system to study mechanisms of nuclear size regulation. To test if the volume of embryonic cytoplasm is limiting for nuclear growth, we encapsulated gastrula stage embryonic cytoplasm and nuclei in droplets of defined volume using microfluidics. Nuclei grew and reached new steady-state sizes as a function of cytoplasmic volume, supporting a limiting component mechanism of nuclear size control. Through biochemical fractionation, we identified the histone chaperone nucleoplasmin (Npm2) as a putative nuclear size-scaling factor. Cellular amounts of Npm2 decrease over development, and nuclear size was sensitive to Npm2 levels both in vitro and in vivo, affecting nuclear histone levels and chromatin organization. Thus, reductions in cell volume with concomitant decreases in Npm2 amounts represent a developmental mechanism of nuclear size-scaling that may also be relevant to cancers with increased nuclear size.

cell biology↗