The mixed-lineage leukaemia gene (MLL/HRX/ALL-1) is disrupted by chromosomal translocation in human acute leukaemias that often display mixed lymphoid-myeloid phenotypes and present in infancy. MLL possesses a highly conserved SET domain also found in Drosophila trithorax (trx) and Polycomb group (Pc-G) genes, which are known to regulate homeotic genes (HOM-C) in a positive or negative fashion, respectively. Mll was targeted in mice by homologous recombination in embryonic stem (ES) cells to assess its role in pattern development. Mll heterozygous (+/-) mice had retarded growth, displayed haematopoietic abnormalities, and demonstrated bidirectional homeotic transformations of the axial skeleton as well as sternal malformations. Mll deficiency (-/-) was embryonic lethal. Anterior boundaries of Hoxa-7 and Hoxc-9 expression were shifted posteriorly in Mll +/- embryos, but their expression was abolished in Mll -/- embryos. Thus Mll is required for proper segment identity in mammals, displays haplo-insufficiency, and positively regulates Hox gene expression.

Unlike humans, who have a continuous row of teeth, mice have only molars and incisors separated by a toothless region called a diastema. Although tooth buds form in the embryonic diastema, they regress and do not develop into teeth. Here, we identify members of the Sprouty (Spry) family, which encode negative feedback regulators of fibroblast growth factor (FGF) and other receptor tyrosine kinase signaling, as genes that repress diastema tooth development. We show that different Sprouty genes are deployed in different tissue compartments--Spry2 in epithelium and Spry4 in mesenchyme--to prevent diastema tooth formation. We provide genetic evidence that they function to ensure that diastema tooth buds are refractory to signaling via FGF ligands that are present in the region and thus prevent these buds from engaging in the FGF-mediated bidirectional signaling between epithelium and mesenchyme that normally sustains tooth development.

Exposure to ultraviolet B (UVB) radiation from the sun can result in sunburn, premature aging and carcinogenesis, but the mechanism responsible for acute inflammation of the skin is not well understood. Here we show that RNA is released from keratinocytes after UVB exposure and that this stimulates production of the inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) from nonirradiated keratinocytes and peripheral blood mononuclear cells (PBMCs). Whole-transcriptome sequencing revealed that UVB irradiation of keratinocytes induced alterations in the double-stranded domains of some noncoding RNAs. We found that this UVB-damaged RNA was sufficient to induce cytokine production from nonirradiated cells, as UVB irradiation of a purified noncoding RNA (U1 RNA) reproduced the same response as the one we observed to UVB-damaged keratinocytes. The responses to both UVB-damaged self-RNAs and UVB-damaged keratinocytes were dependent on Toll-like receptor 3 (TLR3) and Toll-like receptor adaptor molecule 1 (TRIF). In response to UVB exposure, Tlr3−/− mice did not upregulate TNF-α in the skin. Moreover, TLR3 was also necessary for UVB-radiation–induced immune suppression. These findings establish that UVB damage is detected by TLR3 and that self-RNA is a damage-associated molecular pattern that serves as an endogenous signal of solar injury.

SUMMARY The generation of human induced Pluripotent Stem (iPS) cells holds great promise for development of regenerative medicine therapies to treat a wide range of human diseases. However, the generation of iPS cells in the absence of integrative DNA vectors remains problematic. Here we report a simple, highly reproducible RNA-based iPS generation approach that utilizes a single, synthetic self-replicating VEE-RF RNA replicon that expresses four reprogramming factors, OCT4, KLF4, SOX2 with c-MYC or GLIS1 at consistent high levels prior to regulated RNA degradation. A single VEE-RF RNA transfection into newborn or adult human fibroblasts resulted in efficient generation of iPS cells with all the hallmarks of stem cells, including cell surface markers, global gene expression profiles and in vivo pluripotency to differentiate into all three germ layers. The VEE-RF RNA-based approach has broad applicability for the generation of iPS cells for ultimate use in human stem cell therapies in regenerative medicine.