Distinct Expression and Localization of Diacylglycerol Kinase Isozymes in Rat Retina

Abstract

Recent studies have revealed that phosphoinositide (PI) signaling molecules are expressed in mammalian retinas, suggesting their importance in its signal transduction. We previously showed that diacylglycerol kinase (DGK) isozymes are expressed in distinct patterns in rat retina at the mRNA level. However, little is known about the nature and morphological aspects of DGKs in the retina. For this study, we performed immunohistochemical analyses to investigate in the retina the expression and localization of DGK isozymes at the protein level. Here, we show that both DGKβ and DGKι localize in the outer plexiform layer, within which photoreceptor cells make contact with bipolar and horizontal cells. These isozymes exhibit distinct subcellular localization patterns: DGKι localizes to the synaptic area of bipolar cells in a punctate manner, whereas DGKβ distributes diffusely in the subsynaptic and dendritic regions of bipolar and horizontal cells. However, punctate labeling for DGKϵ is evident in the outer limiting membrane. DGKζ and DGKα localize predominantly to the nucleus of ganglion cells. These findings show distinct expression and localization of DGK isozymes in the retina, suggesting a different role of each isozyme.

The Roles of Diacylglycerol Kinases in the Central Nervous System: Review of Genetic Studies in Mice

“…Gene expression profiling of a mouse brain has shown that DGKa is expressed throughout the entire brain (17). In the retinas, DGKa is also expressed in ganglion cells in the ganglion cell layer (GCL) and inner plexiform layer (IPL) (18).…”

“…In the retinas, DGKb is strongly expressed in the rod and cone bipolar cells and horizontal cells of the outer plexiform layer (OPL) and moderately expressed in the inner nuclear layer (INL) and IPL (18).…”

“…DGKe is abundantly expressed in the retina, especially in the INL, outer nuclear layer (ONL), and inner segment layer (ISL), and it is the only isoform expressed in pho toreceptors (18,19,64). In the brain, DGKe is also expressed and distributed in the Purkinje cells of the cerebellum, the pyramidal cells of the hippocampus, the mitral cells of the olfactory bulb, and the neurons of the substantia nigra (27,64).…”

“…Furthermore, in the retinas, DGKz is expressed in the GCL, OPL, INL, and IPL and localized in rod and cone bipolar cells, hori zontal cells, amacrine cells, and ganglion cells (18,19).…”

“…In the brain, DGKi is strongly expressed in the hippocampal calcium region and dentate gyrus, and it is moderately expressed in the cortex and striatum (76). In the retinas, its expression is detected mainly in the postsybaptic region of rod bipolar dendrites in the OPL (18).…”