Student Theses and Dissertations


John Zhao Xue

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Funabiki Laboratory


The eukaryotic nucleus mediates the genomic functions of information storage and gene expression, but must be completely rebuilt after every open mitosis as well as during fertilization. Nuclear abnormalities are observed in many tissue malignancies and congenital disorders, but the causes and effects of such pathologies remain poorly understood. Here we use cell-free Xenopus egg extracts to investigate the contribution of the DNA-binding protein Dppa2 to nuclear assembly. In Dppa2-depleted extracts, nuclei are small and deformed, assemble incomplete nuclear envelopes and fail DNA replication. We show that Dppa2 directly depolymerizes microtubules, and must be localized on DNA to tune local microtubule dynamics for proper nuclear assembly. In the absence of Dppa2, excess microtubules compromise nuclear shape, while ectopically abolishing microtubules retards nuclear expansion. Dppa2 can be bypassed with an appropriate dose oDppa2 nocodazole, but only during a narrow, defined time window. This reveals strict spatial and temporal demands for regulated microtubule dynamics during nuclear formation. We further study the effect of Dppa2 on dynamic microtubule growth reconstituted with purified tubulin, and find that Dppa2 stimulates microtubule catastrophe. This effect is dependent on GTP hydrolysis, and we explore the possibility that Dppa2 activates the intrinsic GTPase activity of microtubule polymers.


A Thesis Presented to the Faculty of The Rockefeller University In Partial Fulfillment of the Requirements for The degree of Doctor of Philosophy

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