Figure 6: Comparative Tissue Expression for Human PTL-like Genes (PTL, PLR1, PLR2 and PLR3). Expression ‘heat maps’ (GNF Expression Atlas 2 data) [64] were examined for comparative gene expression levels among human tissues for PTL, PLR1, PLR2 and PLR3 genes showing high (red); intermediate (black); and low (green) expression levels; derived from human genome browser.