Djck1 alpha Is Required for Proper Regeneration and Maintenance of the Medial Tissues in Planarians

CK1 alpha (Casein kinase 1 alpha) is a member of the casein kinase 1(CK1) family that is involved in diverse cellular processes, but its functions remain unclear in stem cell development. Freshwater planarians are capable of whole-body regeneration, making it a classic model for the study of regeneration, tissue homeostasis, and polarity in vivo. To investigate the roles of CK1 alpha in regeneration and homeostasis progress, we characterize a homolog of CK1 alpha from planarian Dugesia japonica. We find that Djck1 alpha, which shows an enriched expression pattern in the nascent tissues, is widely expressed especially in the medial regions of planarians. Knockdown of CK1 alpha by RNAi presents a thicker body due to dorsal hyperplasia, along with defects in the medial tissues including nerve proliferation, missing epidermis, intestine disturbance, and hyper-proliferation during the progression of regeneration and homeostasis. Moreover, we find that the ck1 alpha RNAi animals exhibit expansion of the midline marker slit. The eye deficiency induced by slit RNAi can be rescued by ck1 alpha and slit double RNAi. These results suggest that ck1 alpha is required for the medial tissue regeneration and maintenance in planarian Dugesia japonica by regulating the expression of slit, which helps to further investigate the regulation of planarian mediolateral axis.