Fig. 1: Genetic ablation of either Nme1 or Nme2 confers strong metastatic activity to UV-induced melanomas in hepatocyte growth factor (HGF): p16^−/− (HP) mice.

a Organisation of the Nme1 and Nme2 genes and strategy for selective disruption of each in transgenic mouse strains. “Nme1:Nme2” depicts the genomic Nme1: Nme2 locus in the mouse. The structural Nme1 gene is denoted in yellow, with exons represented by blue squares. Translational initiation (ATG) and termination (TGA, TAG) codons are also identified within both genes. Nme2 is denoted in green, with exons represented by brown squares. The sequence labelled “ΔNme1” portrays the insertion of a LacZ-NEO cassette within intron 1 of the Nme1 gene, preventing transcription for downstream coding exons 2–4 (denoted in the diagram as Δ, and outlined by the translucent blue box) while sparing expression of Nme2.⁸ “ΔNme2” depicts the deletion of exons 4 and 5 within the Nme2 gene, resulting in expression of a truncated transcript that is unstable and poorly translated.⁹ b Diagram illustrates the three strains of mice employed in the study. The “HP” strain was engineered for overexpression of HGF and homozygous deletion of the Ink4a/p16 locus (p16^−/−).¹⁰ Strains “HPN1” and “HPN2” represent hybrid crosses of the HP strain with mice harbouring either the ΔNme1 or ΔNme2 genotypes in the homozygous form (“Nme1^Δ/Δ” or “Nme2^Δ/Δ”), as shown. c Protocol for ultraviolet radiation (UVR) initiation and monitoring of melanomas in HP-based mouse strains. d Images of primary melanomas, lungs, and proximal lymph nodes from representative HP, HPN1 and HPN2 mice (numbers following HP/HPN genotype indicate mouse identifiers). Macroscopic photographs of tissues are displayed in the top set of three images for each mouse, with volumes of primary melanomas (1^o), lung metastasis scores, and lymph-node enlargement scores provided below the corresponding images. Representative microscopic images of haematoxylin/eosin-stained tissue sections are shown below each corresponding macroscopic image (scale bars represent 50 μm). e Summaries of lung metastasis and lymph-node enlargement scores for all melanoma-positive HP, HPN1 and HPN2 mice. Lung metastasis and lymph-node scores for HPN1 and HPN2 mice were compared to those of HP mice using the Mann–Whitney rank-sum test, with probabilities displayed within the corresponding panels.