In the Eyes of the Beholder-New Knockout Mouse and Re-Evaluation of Phagocytosis versus Anti-Inflammatory Functions of MERTK.

Greg Lemke's laboratory was one of the pioneers of research into the TAM family of receptor tyrosine kinases (RTKs). Not only was cloned in his laboratory, but his group also extensively studied mice knocked out for individual or various combinations of the TAM RTKs , , and . Here we primarily focus on one of the paralogs-MERTK. We provide a historical perspective on rodent models of loss of function and their association with retinal degeneration and blindness. We describe later studies employing mouse genetics and the generation of newer knockout models that point out incongruencies with the inference that loss of MERTK-dependent phagocytosis is sufficient for severe, early-onset photoreceptor degeneration in mice. This discussion is meant to raise awareness with regards to the limitations of the original knockout mouse model generated using 129 derived embryonic stem cells and carrying 129 derived alleles and the role of these alleles in modifying knockout phenotypes or even displaying -independent phenotypes. We also suggest molecular approaches that can further Greg Lemke's scintillating legacy of dissecting the molecular functions of MERTK-a protein that has been described to function in phagocytosis as well as in the negative regulation of inflammation.