Stitching the seams together

Epithelial cell shape changes are important in many developmental processes, including the formation of the postembryonic epidermis in nematodes. On p. 223, Masako Asahina and colleagues describe the involvement of the nuclear hormone receptor NHR-25 in this process. The worm epidermis consists of the hyp 7 syncytium, the hypodermal cells of the head and tail, interfacial epithelial cells, the ventral P cells, and the seam cells. The authors use RNAi to show that in absence of NHR-25 the seam cells do not elongate properly and fail to reestablish the contacts with neighbouring seam cells that are lost following each asymmetric cell division. This compromises the fate of seam-cell anterior daughters and produces a cuticle that has abnormal ridges. Unexpectedly, the loss of cell-cell contacts does not prevent the unique seam cell V5.p producing the neuroblast needed for formation of the postdeirid, a sensory organ, which was previously seen in seam-cell ablation experiment. Silencing of nhr-25 also disrupts epidermal cell morphology and moulting, and the authors conclude that NHR-25 plays distinct roles in cell-shape dynamics and moulting during epidermal development.