Nuclear morphology is typically ellipsoid, and this shape is conserved across tissues and species. Nuclei that are lobular or misshapen are rarely seen in healthy cells, and are more often associated with various disease states. Understanding nuclear shape changes in healthy cells is therefore difficult, as there are few models with which to work. In their Research Article (Arbach et al., 2018), Andrea Wills and colleagues present the first characterisation of elaborately branched nuclear morphologies in a diverse population of healthy epidermal cells that make up the Xenopus tropicalis tail fin. The authors examine the nuclear morphology in the differentiated fin and find that the entire nucleus of fin marginal cells is branched. These cells appear healthy, with active enhancer marks and heterochromatin found throughout the nuclear branches; they are also able to undergo mitosis, and so have active cell cycles. The authors show that the nuclear branching requires intact F-actin, but not microtubules, as well as functional Lamin B1 in the epidermis; mechanical swimming forces, however, are not required, but do contribute to fin morphology. These data provide new insight into the molecular basis for nuclear branching, and introduce a new system for the study of extreme morphological variation in healthy tissue.
