gamma-Tubulin small complex formation is essential for early zebrafish embryogenesis

The centrosomal protein gamma-tubulin is part of the cytoplasmic gamma-tubulin small (gamma-TuSCs) and large complexes (gamma TuRCs). Both, molecular and cellular evidence indicate that gamma-tubulin plays a central role in microtubule nucleation and mitotic spindle formation. However, the molecular mechanisms of complex formation and subsequent biological roles in animal development remain unclear. Here, we used gamma-tubulin gene knockdown in the zebrafish early embryo model to gain insights into its activity and cellular contribution during vertebrate embryogenesis. gamma-Tubulin loss-of-function impaired gamma-TuSC formation, impacting the microtubule nucleation rate in vitro. Moreover, decreased gamma-tubulin synthesis caused dramatic defects in nuclear dynamics and cell cycle progression, leading to developmental arrest at the mid-gastrula stage. At the subcellular level, microtubule organization and function were altered, affecting chromosome segregation and triggering cell proliferation arrest and apoptosis. Our results suggest that de novo translated gamma-tubulin participates in gamma-TuSC formation required for early animal development. Importantly, formation of this complex is essential for both centrosome assembly and function, and cell proliferation. Thus, gamma-TuSC integrity appears to be critical for cell cycle progression, and concomitantly, for coordinating the many distinct activities carried out by the early embryo. Our findings identify a novel role for gamma-TuSC in the regulation of early vertebrate embryogenesis, providing molecular and biochemical starting points for future in depth studies of gamma-tubulin functionality and its specific role in development.