Haploid cells have only one set of chromosomes, and therefore are a valuable tool in genetic screening and transgenic animal production. In previous studies, mammalian haploid embryonic stem cells have been established. However, since haploid embryonic stem cells undergo spontaneous diploidization during culture and differentiation, there are challenges in establishing haploid somatic cells and somatic cell-based genetic screening system.
Recently, Dr. Qi Zhou and his team from the Institute of Zoology, Chinese Academy of Sciences (CAS), discovered, through cell cycle analysis using live cell imaging, that mitotic slippage is the primary cause of diploidization of mouse haploid embryonic stem cells. By screening with small molecule inhibitors involved in metaphase regulation, they found that the CDK1 and ROCK pathways are the key pathways in regulating diploidization of haploid embryonic stem cells. Through ROCK inhibition, haploid embryonic stem cells can differentiate into haploid somatic cells of all three germ layers, including neural stem cells (which can further differentiate into mature neurons and astrocytes), cardiomyocytes and islet cells. Moreover, using piggyBac transposon-based insertional mutagenesis, they generated a haploid neural cell library harboring genome-wide mutations for genetic screening, and identified the important role of Park2 gene in Mn2+-mediated toxicity as a proof of concept through screening.
The findings not only expand the application of haploid cell technology to somatic cell types, but also shed light on the mechanisms of ploidy maintenance. The relevant paper entitled "Generation of mouse haploid somatic cells by small molecules for genome-wide genetic screening" is published online in Cell Reports on August 29, 2017 (http://www.cell.com/cell-reports/fulltext/S2211-1247(17)31101-4).
The research is supported by Ministry of Science and Technology, National Natural Science of China, and CAS Strategic Priority Research Program.
Diagram: Establishment and genetic screening of haploid somatic cells.