Mammalian Tolloid-like 1 (mTll1) is one of the four Tolloid proteins that are pleiotropic, astacin-like metalloproteases. This protein is expressed at high levels in the granular layer of the cerebellum of adult mice (30) and in the hippocampus of both juvenile and adult mice (31). The hippocampus is a direct target of stress hormones (32). Cerebellum plays important roles in emotion processing and fear conditioning through connecting with the hypothalamic-pituitary-adrenal axis (33). Studies have found that the development of cerebellum is more dependent on environmental factors than most other brain regions (34). It has been consistently shown that children and adolescents with a history of maltreatment have decreased cerebellar volume (35,36). Although TLL1 has not been previously associated with PTSD, functional studies suggest that glucocorticoids, which regulate stress response in mammals, could decrease mTll1 expression in vitro (31). An elevated number of hippocampal neurons expressing mTll1 were found in mice with increased neurogenesis, which is related to the stress response (31,37). Research on reptilian orthology of TLL1 isolated from turtle showed that the gene cleaves the precursor pro-brain-derived neurotrophic factor
