Apoc1 is a marker of phagocytic microglia in retinal development
Author : Dillon Heffernan
Orange High School
The retina is a light-sensitive tissue responsible for transmitting light signals to the brain, which then processes these signals into what we see. Like all tissues, proper blood vessel development, or angiogenesis, is essential for retinal health and development (Reichenback, n.d 2021). Two types of glial cells in the retina, astrocytes, and microglia play unique but critical roles in retinal angiogenesis. Astrocytes provide a physical template for angiogenesis in the nerve fiber layer (top-most level of the retina) starting from the center of the retina, or the optic nerve and proceeding towards the outer edge of the retina, or periphery, shortly after birth in the mouse (Puñal et al., 2019 ). Interestingly, astrocytes are culled over 3-fold from P5 to P14, hereafter referred to as the dead period, and microglia facilitate a significant amount of this astrocyte death by phagocytosing astrocytes (Vecino, n.d 2015). A previous single-cell RNA sequencing experiment from our lab (Duke Kay Lab) identified Apoc1 as a novel marker of phagocytic microglia. The goal of this project was to define Apoc1 expression in microglia spatially and temporally by in situ hybridization at two different mouse retinal development ages, postnatal (P) day 5 and day 17. The images taken at 60x were quantified and displayed that microglia express Apoc1 only during the astrocyte death period and not at P17, which is after retinal angiogenesis has concluded, suggesting it primarily plays a role in microglia that phagocytose astrocytes. It was also concluded that Apoc1 gene expression increases from a central-to-peripheral gradient.