Zebrafish cdc6 hypomorphic mutation causes Meier-Gorlin syndrome-like phenotype

Abstract

Cell Division Cycle 6 (Cdc6) is a component of pre-replicative complex (preRC) forming on DNA replication origins in eukaryotes. Recessive mutations in ORC1, ORC4, ORC6, CDT1 or CDC6 of the preRC in human cause Meier-Gorlin syndrome (MGS) that is characterized by impaired post-natal growth, short stature andmicrocephaly. However, vertebratemodels of MGS have not been reported. Through N-ethyl-N-nitrosoureamutagenesis and Cas9 knockout, we generate several cdc6mutant lines in zebrafish. Loss-of-functionmutations of cdc6, asmanifested by cdc6tsu4305 and cdc6tsu7cd mutants, lead to embryonic lethality due to cell cycle arrest at the S phase and extensive apoptosis. Embryos homozygous for a cdc6 hypomorphicmutation, cdc6tsu21cd, develop normally during embryogenesis. Later on, compared with their wild-type (WT) siblings, cdc6tsu21cdmutant fish show growth retardation, and their body weight and length in adulthood are greatly reduced, which resemble human MGS. Surprisingly, cdc6tsu21cd mutant fish becomemales with a short life and fail tomate withWT females, suggesting defective reproduction. Overexpression of Cdc6mutant forms, whichmimic human CDC6(T323R) mutation found in a MGS patient, in zebrafish cdc6tsu4305 mutant embryos partially represses cell death phenotype, suggesting that the human CDC6(T323R) mutation is a hypomorph. cdc6tsu21cd mutant fish will be useful to detect more tissue defects and developmedical treatment strategies for MGS patients.