HOXA9 and leukemia: Interestingly, KEGG enrichment analysis identified many amino acid metabolic pathways significantly overexpressed in Tg(drl:hoxa9;hsp70:meis1), such as tryptophan metabolism, glycine and serine, glutamate, and arginine metabolism (electronic supplementary material, figure S4), indicating that the dysregulated amino acid metabolism is probably involved in the myeloid malignancies in Tg(drl:hoxa9;hsp70:meis1), which is consistent with recent studies showing the elevated amino acid metabolism in leukaemia stem cells and primary blasts [51,52].