ABSTRACT
Retinal ganglion cell axons exit the eye, enter the optic stalk, cross the ventral midline at the optic chiasm, and terminate in the optic tectum of the zebrafish. While in the optic stalk, they grow immediately adjacent to cells expressing the powerful retinal axon repellent slit2. The chemokine stromal cell-derived factor-1 (SDF1) is expressed within the optic stalk and its receptor CXCR4 is expressed in retinal ganglion cells. SDF1 makes cultured retinal axons less responsive to slit2. Here, we show that reducing SDF1 signaling in vivo rescues retinal axon pathfinding errors in zebrafish mutants that have a partial functional loss of the slit receptor robo2. In contrast, reducing SDF1 signaling in animals that completely lack the robo2 receptor does not rescue retinal guidance errors. These results demonstrate that endogenous levels of SDF1 antagonize the repellent effects of slit/robo signaling in vivo and that this antagonism is important during axonal pathfinding.
Subject(s)
Chemokines, CXC/physiology , Intracellular Signaling Peptides and Proteins/antagonists & inhibitors , Receptors, Immunologic/antagonists & inhibitors , Signal Transduction/physiology , Zebrafish Proteins/physiology , Animals , Cells, Cultured , Chemokine CXCL12 , Chemokines, CXC/genetics , Gene Expression Regulation, Developmental/physiology , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/physiology , Receptors, CXCR4/biosynthesis , Receptors, CXCR4/genetics , Receptors, Immunologic/biosynthesis , Receptors, Immunologic/genetics , Retinal Ganglion Cells/metabolism , Zebrafish , Zebrafish Proteins/antagonists & inhibitors , Zebrafish Proteins/biosynthesis , Zebrafish Proteins/geneticsABSTRACT
The G protein beta gamma-dimer is required for receptor interaction and effector regulation. However, previous approaches have not identified the physiologic roles of individual subtypes in these processes. We used a gene knockout approach to demonstrate a unique role for the G protein gamma(7)-subunit in mice. Notably, deletion of Gng7 caused behavioral changes that were associated with reductions in the alpha(olf)-subunit content and adenylyl cyclase activity of the striatum. These data demonstrate that an individual gamma-subunit contributes to the specificity of a given signaling pathway and controls the formation or stability of a particular G protein heterotrimer.
