Abstract
Purpose :
Very little is currently known about the molecular factors that control the fates of the many types of retinal ganglion cells (RGCs) during retinal development. By using a mouse knockout of Satb2 (Satb2fl/fl) and ectopic Satb2 expression, this study investigates the role of the transcription factor Satb2 in direction-selective RGC (DS-RGC) specification.
Methods :
Satb2 conditional KO and the Pax6-Cre mice were bred. Expression of the DS-RGC marker CART was examined through immunofluorescence on P10 eye sections from mice that had Satb2 knocked out early in development and littermate controls. In order to visualize the axonal connections in the brain, Satb2fl/fl; Pax6-Cre mice were crossed to the DRD4-GFP line, in which a population of DS-RGCs are labeled with GFP. The GFP+ axons target the lateral geniculate nucleus (LGN) and superior colliculus (SC). All RGCs in the resulting mice were labeled with a whole-eye fill and their brains were harvested at P10 to investigate axon targeting in LGN and SC.
Satb2 ectopic expression in the retina was performed in vivo through a lentiviral vector delivery at E15.5. A virus that expresses only a fluorescent reporter was used as a control. We quantified the population of cells infected with Satb2 and control virus that coexpressed CART in P8 retinal sections.
Results :
There is a dramatic loss of CART+ cells in the Satb2 KO retina when compared to wildtype (n=3 retinas of each type). Ectopic Satb2 expression in a random population of RGCs doubles the number of CART positive RGCs compared to RGCs infected with control virus. In the Satb2 knockout mice, there is a complete loss of GFP+ inputs to the LGN and SC (n=4 mice).
Conclusions :
Our results are consistent with the hypothesis that Satb2 plays a role in establishing DS-RGC identity. The loss of CART+ RGCs in the Satb2 KO retina indicates that Satb2 is necessary for the expression of CART in DS-RGCs. The increase in number of cells expressing CART in a random group of Satb2-virus infected RGCs indicates that Satb2 is also sufficient for inducing CART expression in DS-RGCs. The lack of GFP+ axons in the SC and LGN of KO mice suggests that Satb2 may be an upstream regulator of Drd4 and thus disrupts GFP expression, or more interestingly, Satb2 is also regulating genes involved in axon targeting. Together, this evidence supports the idea that Satb2 is a regulator of at least some aspects of DS-RGC fate.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.