Zinc finger protein Zfp335 is required for the formation of the naive T cell compartment

The generation of naive T lymphocytes is critical for immune function yet the mechanisms governing their maturation remain incompletely understood. Through ENU mutagenesis screening, we identified a mouse mutant, bloto, characterized by a deficiency in naive T cells. The causative genetic lesion was identified as a hypomorphic mutation in the zinc finger protein Zfp335. Zfp335bloto/bloto mice had a paucity of naive T lymphocytes due to a cell-intrinsic defect in mature thymocytes, as well as in peripheral T cells that have recently undergone thymic egress. The T cell defect in Zfp335bloto/bloto mice could not be explained by altered thymic selection, proliferation or Bcl2-dependent survival. ChIP-seq analysis revealed that Zfp335 binds primarily to promoter regions, and we identified a set of target genes in thymocytes that are enriched in categories related to protein metabolism, mitochondrial function, and transcriptional regulation. Our analysis also showed that Zfp335bloto occupancy at a subset of sites was significantly decreased, and that this reduced binding correlated with deregulated target gene expression. Restoring the expression of one target, Ankle2, partially rescued T cell maturation. Finally, we identified a new DNA recognition motif and demonstrated that it was bound by Zfp335 in vitro. We suggest that Zfp335 binds directly to DNA in a sequence-specific manner to control gene transcription and in doing so, functions as an essential regulator of late-stage intrathymic and post-thymic T cell maturation.