Nuclear movements are important for a wide range of cellular and developmental processes, but whereas the intracellular mechanisms of nuclear movement have been studied in detail, the role of surrounding cells remains poorly understood. Now, on , Carl-Philipp Heisenberg and colleagues reveal that, during zebrafish gastrulation, the nuclear movements seen in the yolk syncytial layer(YSL) are guided by surrounding tissues. Some yolk syncytial nuclei (YSN) are located below a tissue called the mesendoderm, which contains mesoderm and endoderm progenitors. During gastrulation, the movements of these YSN and of the mesendoderm are very similar. The authors demonstrate that these movements are coordinated, and that the mesendoderm directs YSN movements by modulating cortical flow (a concerted flow of actin filaments associated with the plasma membrane) within the YSL, which contains the YSN. They also find that the coordinated movement of the YSN and the mesendoderm requires E-cadherin. Thus,they propose, nuclear movements can be guided by surrounding tissues and are mediated by cortical flow.
