Ten-eleven translocation (TET) methylcytosine dioxygenase has potential as an active eraser to regulate the genomic DNA methylation status. We herein cloned chicken TET (cTET) family genes, and confirmed their functions. Quantitative reverse-transcription PCR showed that cTET1 was strongly expressed in erythrocytes throughout development. This cTET1 1 expression pattern, together with the results of methylated or hydroxymethylated DNA immunoprecipitation, suggests that cTET1 contributes to demethylation around the promoter region of the definitive-type-beta-globin gene beta A in erythroid cells. The knockdown of cTET1 in T2ECs chicken erythroid progenitor cells suppressed the induction of beta A expression under differentiation conditions. These results suggest that cTET1 plays an important role in erythroid cell differentiation. (C) 2017 Elsevier Inc. All rights reserved.