Gene Expression Variability and Nuclear Territory Autonomy in Syncytia

合胞体中基因表达变异与核领域自主

Title Gene expression variability and nuclear territory autonomy in syncytia Project Summary Syncytia are large, multinucleate cells that are found widely across biology. Algae, fungi, protists, and human tissues like muscle and placenta are all composed of syncytia. Such organization has even been proposed to be the ancestral eukaryotic state. Despite its prevalence across kingdoms of life, the organization and regulation of syncytial cells remain understudied. How do multiple nuclei shape the composition and function in syncytia? Syncytial algal and mammalian muscle cells show distinct gradients of local composition. Nuclei sharing the same cytoplasm in these cells show distinct transcriptional profiles. Work in the Gladfelter lab showed that in the syncytial fungus Ashbya gossypii, nuclei show asynchronous nuclear division, suggesting that cell-cycle signals are not shared in neighboring nuclei in these cells. Overall, these pieces of evidence suggest that the cytosolic composition in syncytial cells is highly heterogeneous despite lacking physical barriers to diffusion across the cell, and that syncytial nuclei can show autonomy in gene expression. It is unknown how the composition of nuclear-proximal cytosolic territories is regulated in syncytia, and how this impacts nuclear territory function. Extensive work in the Gladfelter lab has revealed that spatial clustering and non-random localization of transcripts underlies nuclear-autonomous division in Ashbya. Such non-random localization is mediated by the formation of RNA-protein condensates consisting of Whi3 protein. Whi3 condensates also modulate proper branching morphology in Ashbya by clustering transcripts involved in polar growth at hyphal tips. How Whi3 localization modulates translation from these transcripts in unknown. In general, it is unknown how nuclear territory composition and function are regulated by local variation in transcription and translation. In this proposal I will examine how local composition is influenced by spatial variability in transcription and translation in the genetically tractable model syncytial fungus Ashbya. In Aim 1 I will investigate sources of transcription variation between nuclei and the consequences of such variation on local territory function. By modulating transcription locally, I expect to establish the role of nuclear autonomous transcription in controlling variation in local biochemical function. In Aim 2 I will investigate the role of Whi3 condensation on spatial biases in translation. I will use manipulate Whi3 condensation locally to study the impact of condensates on local translation. In Aim 3 I will investigate which biochemical processes are globally coordinated versus those that are locally responsive across syncytial nuclei. This will reveal nuclear populations that show active or repressed transcription, and biochemical processes that are locally regulated. Upon the completion of this work, I expect to dissect the contribution of variation in transcription and regulated local translation in shaping the functionality of nucleus-associated cytosolic territories in Ashbya. The rationale for the proposed work is that it will provide insight into how local autonomy of nuclear territories can shape the biology of large multinucleate cells. Overall, this work will provide insights into organization and regulation of a widespread yet poorly understood cell-type.