Retrotransposon Gag-like protein 9 (RTL9)

Retrotransposon Gag-like protein 9 (RTL9) is a eutherian-conserved protein encoded by the human gene RTL9 (also known as RGAG1, SIRH10, among other aliases)[1][4]. It belongs to the family of retrovirus-derived Gag-like LTR retrotransposon products, specifically related to the Ty3/gypsy retrotransposon family, but has lost essential structural or enzymatic functions of its viral ancestor[3][5]. RTL9 protein is highly expressed in the testis and at low levels in the brain, heart, and ovary[1][4]. Functional studies in mice indicate that RTL9 is a microglia-expressed protein localized in lysosomes, where it promotes degradation of fungal zymosan—a complex fungal cell wall component—thus contributing to brain innate immunity against fungal pathogens[1]. Knockout of Rtl9 leads to failure of zymosan degradation in microglial lysosomes, implicating its essential role in this context, though the precise biochemical mechanism remains unclear and it is not currently considered to have enzymatic activity[1]. There are no known approved drugs, biomarkers, safety concerns, or direct therapeutic relevance for human disease at this time[4][6].

Other names

RGAG1KIAA1318Mart9Mar9SIRH10retrotransposon Gag domain-containing protein 1tumor antigen BJ-HCC-23Sushi-Ichi retrotransposon homolog 10mammalian retrotransposon-derived 9MAR9MART9retrotransposon gag domain containing 1retrotransposon gag domain-containing protein 1tumor antigen BJHCC23