Source: Academia Sinica

Cell division is a fundamental process for life. Besides mitosis in somatic cells and meiosis in germ cells, a research team led by Dr. Chen-Hui Chen at the Institute of Cellular and Organismic Biology, Academia Sinica discovered a deviant form of cell division in live zebrafish larvae that accounts for a drastic increase of cell number during development. The study is published in April 2022 in the journal Nature.

As an animal’s surface area expands during development, skin cell populations must quickly respond to maintain sufficient epithelial coverage. Despite much progress in our understanding of skin cell behaviors in vivo, it remains unclear how cells collectively act to satisfy coverage demands at an organismic level. Here, we created a multicolor cell membrane tagging system, palmskin, to monitor the entire population of superficial epithelial cells (SECs) in developing zebrafish larvae. Using time-lapse imaging, we found that many SECs readily divide on the animal body surface; during a specific developmental window, a single SEC can produce a maximum of four progeny cells over its lifetime on the surface of the animal. Remarkably, EdU assays, DNA staining, and Hydroxyurea treatment revealed that these terminally differentiated skin cells continue splitting despite an absence of DNA replication, causing up to 50% of SECs to exhibit a reduced genome size. 

Based on a simple mathematical model and quantitative analyses of cell volumes and apical surface areas, we propose that ‘asynthetic fission’ is utilized as an efficient mechanism for expanding epithelial coverage during rapid growth. Furthermore, global or local manipulation of body surface growth affects the extent and mode of SEC division, presumably through tension-mediated activation of stretch-activated ion channels. We speculate that this frugal yet flexible mode of cell proliferation might also occur in contexts other than zebrafish skin expansion.

This study is supported by Academia Sinica Career Development Award, the Institute of Cellular and Organismic Biology at Academia Sinica, and the Ministry of Science and Technology, Taiwan.