Overexpression of MMACHC Prevents Craniofacial Phenotypes Caused by Knockdown of znf143b

ZNF143 is a sequence-specific DNA binding protein that regulates the expression of protein-coding genes and small RNA molecules. In humans, ZNF143 interacts with HCFC1, a transcriptional cofactor, to regulate the expression of downstream target genes, including MMACHC, which encodes an enzyme involved in cobalamin (cbl) metabolism. Mutations in HCFC1 or ZNF143 cause an inborn error of cobalamin metabolism characterized by abnormal cbl metabolism, intellectual disability, seizures, and mild to moderate craniofacial abnormalities. However, the mechanisms by which ZNF143 mutations cause individual phenotypes are not completely understood. Defects in metabolism and craniofacial development are hypothesized to occur because of decreased expression of MMACHC. But recent results have called into question this mechanism as the cause for craniofacial development. Therefore, in the present study, we implemented a loss of function analysis to begin to uncover the function of ZNF143 in craniofacial development using the developing zebrafish. The knockdown of znf143b, one zebrafish ortholog of ZNF143, caused craniofacial phenotypes of varied severity, which included a shortened and cleaved Meckel's cartilage, partial loss of ceratobranchial arches, and a distorted ceratohyal. These phenotypes did not result from a defect in the number of total chondrocytes but were associated with a mild to moderate decrease in mmachc expression. Interestingly, expression of human MMACHC via endogenous transgene prevented the onset of craniofacial phenotypes associated with znf143b knockdown. Collectively, our data establishes that knockdown of znf143b causes craniofacial phenotypes that can be alleviated by increased expression of MMACHC.