NRAS and melanoma: Therefore, our hypothesis was that keratinocytic Rxrα ablation when combined with homozygous activated Cdk4R24C/R24C and heterozygous expression of human NRAS (Tyr-NRASQ61K) would result in enhanced formation of spontaneous malignant melanoma, which would be further aggravated/ accelerated by a single neonatal UVB-irradiation in the trigenic mouse model.