Loss of Setd4 delays radiation-induced thymic lymphoma in mice

Radiation-induced lymphomagenesis results from a clonogenic lymphoid cell proliferation due to genetic alterations and immunological dysregulation. Mouse models had been successfully used to identify risk and protective factors for radiation-induced DNA damage and carcinogenesis. The mammalian SETD4 is a poorly understood putative methyl-transferase. Here, we report that conditional Setd4 deletion in adult mice significantly extended the survival of radiation-induced T-lymphoma. However, in Tp53 deficient mice, Setd4 deletion did not delay the radiation-induced lymphomagenesis although it accelerated the spontaneous T-lymphomagenesis in non-irradiated mice. The T-lymphomas were largely clonogenic in both Setd4^flox/flox and Setd4^Δ/Δ mice based on sequencing analysis of the T-cell antigen β receptors. However, the Setd4^Δ/Δ T-lymphomas were CD4⁺/CD8⁺ double positive, while the littermate Setd4^flox/floxtumor were largely CD8+ single positive. A genomic sequencing analysis on chromosome deletion, inversion, duplication, and translocation, revealed a larger contribution of inversion but a less contribution of deletion to the overall chromosome rearrangements in the in Setd4^Δ/Δ tumors than the Setd4^flox/flox tumors. In addition, the Setd4^flox/flox mice died more often from the large sizes of primary thymus lymphoma at earlier time, but there was a slight increase of lymphoma dissemination among peripheral organs in Setd4^Δ/Δ at later times. These results suggest that Setd4 has a critical role in modulating lymphomagenesis and may be targeted to suppress radiation-induced carcinogenesis.

Embryogenic stem cell-derived intestinal crypt fission directs de novo crypt genesis

Intestinal epithelial replenishment is fueled by continuously dividing intestinal stem cells (ISCs) resident at the crypt niche. However, the cell type(s) enabling replenishment upon damage and subsequent loss of whole crypts remain largely unclear. Using Set domain-containing protein 4 (Setd4), we identify a small population with reserve stem cell characteristics in the mouse intestine. Upon irradiation-induced injury, Setd4-expressing (Setd4⁺) cells survive radiation exposure and then activate to produce Sca-1-expressing cell types to restore the epithelial wall and regenerate crypts de novo via crypt fission. Setd4⁺ cells are confirmed to originate from the early fetal period, subsequently contributing to the development of embryonic gut and the establishment of postnatal crypts. Setd4⁺ cells are therefore represented as both originators and key regenerators of the intestine.