Gamma-tubulin coordinates nuclear envelope assembly around chromatin

Abstract

The cytosolic role of γ-tubulin as a microtubule organizer has been studied thoroughly, but its nuclear function is poorly understood. Here, we show that γ-tubulin is located throughout the chromatin of demembranated Xenopus laevis sperm and, as the nucleus is formed, γ-tubulin recruits lamin B3 and nuclear membranes. Immunodepletion of γ-tubulin impairs X. laevis assembly of both the lamina and the nuclear membrane. During nuclear formation in mammalian cell lines, γ-tubulin establishes a cellular protein boundary around chromatin that coordinates nuclear assembly of the daughter nuclei. Furthermore, expression of a γ-tubulin mutant that lacks the DNA-binding domain forms chromatin-empty nuclear like structures and demonstrate that a constant interplay between the chromatin-associated and the cytosolic pools of γ-tubulin is required and, when the balance between pools is impaired, aberrant nuclei are formed. We therefore propose that the nuclear protein meshwork formed by γ-tubulin around chromatin coordinates nuclear formation in eukaryotic cells.