Tissue-specific modifier alleles determine Mertk loss-of-function traits

Area of Science:

• Genetics
• Immunology
• Ophthalmology

Background:

• Knockout (KO) mouse models are essential for understanding gene function and disease mechanisms.
• The Mertk receptor tyrosine kinase is implicated in phagocytosis and various cellular processes.
• Mertk KO mice have been associated with retinal degeneration and altered anti-tumor immunity.

Purpose of the Study:

• To investigate the precise genetic basis for phenotypes observed in Mertk KO mice.
• To determine if Mertk loss alone is sufficient to cause observed traits.
• To elucidate the role of genetic modifiers in Mertk KO phenotypes.

Main Methods:

• Analysis of the genetic background of commonly used Mertk KO mouse lines.
• Phenotypic characterization of Mertk KO mice with and without functional Tyro3.
• Assessment of anti-tumor immunity in different genetic contexts.

Main Results:

• Widely used Mertk KO mice possess unintended genomic alterations affecting other genes, including Tyro3.
• Retinal degeneration in Mertk KO mice requires the concurrent loss of Tyro3.
• Enhanced anti-tumor immunity in Mertk KO mice is not solely due to Mertk deficiency and is not explained by Tyro3 or macrophage redundancy.

Conclusions:

• Phenotypes attributed to Mertk KO are often influenced by genetic background and epistasis.
• The loss of Mertk alone is insufficient to cause retinal degeneration or fully explain altered anti-tumor immunity.
• Context-dependent epistasis of modifier alleles dictates Mertk KO traits.