Analysis of the CaMKIIα and β splice-variant distribution among brain regions reveals isoform-specific differences in holoenzyme formation

Abstract

Four CaMKII isoforms are encoded by distinct genes, and alternative splicing within the variable linker-region generates additional diversity. The α and β isoforms are largely brain-specific, where they mediate synaptic functions underlying learning, memory and cognition. Here, we determined the α and β splice-variant distribution among different mouse brain regions. Surprisingly, the nuclear variant αB was detected in all regions, and even dominated in hypothalamus and brain stem. For CaMKIIβ, the full-length variant dominated in most regions (with higher amounts of minor variants again seen in hypothalamus and brain stem). The mammalian but not fish CaMKIIβ gene lacks exon v3N that encodes the nuclear localization signal in αB, but contains three exons not found in the CaMKIIα gene (exons v1, v4, v5). While skipping of exons v1 and/or v5 generated the minor splice-variants β’, βe and βe’, essentially all transcripts contained exon v4. However, we instead detected another minor splice-variant (now termed βH), which lacks part of the hub domain that mediates formation of CaMKII holoenzymes. Surprisingly, in an optogenetic cellular assay of protein interactions, CaMKIIβH was impaired for binding to the β hub domain, but still bound CaMKIIα. This provides the first indication for isoform-specific differences in holoenzyme formation.

Heterogeneity in human hippocampal CaMKII transcripts reveals allosteric hub-dependent regulation

“…This splice variant plays an important role in membrane anchoring using its hydrophobic N-terminal domain (28). Finally, it was shown that alternative splicing within the hub might regulate oligomerization (5). Roles for the remaining exons have yet to be delineated.…”

“…CaMKII is expressed throughout the human body, which facilitates its role in these disparate functions. There are four human genes that encode CaMKII: CaMKIIα and β (predominantly in brain), CaMKIIδ (predominant in heart) and CaMKIIγ (multiple organ systems, including egg and sperm) (5)(6)(7). In all four genes, each CaMKII subunit is comprised of a kinase domain, regulatory segment, variable linker region, and a hub domain (Fig.…”

CaMKIIβ in Neuronal Development and Plasticity: An Emerging Candidate in Brain Diseases

“…It should be mentioned that the variable region, where CaMKIIα and β differ most, is subject to alternative splicing in all CaMKII isoforms. Regarding CaMKIIβ, four splicing variants, β, β’, βe, and β’e, were discovered in the brain, but only β and β’variants contain a FABD and are, therefore, able to bind to F-actin [ 10 , 11 , 12 , 13 ] ( Figure 1 A).…”

“…In the mature brain, the full-length variant CaMKIIβ predominate in most brain regions, except in the hypothalamus and brainstem where equal β and β’ are detected [ 11 ]. In the whole embryonic brain, βe predominate at E16 and E18 [ 11 ]. However, in the embryonic cerebral cortex, β and β’ proteins are dominant at E16.5 [ 18 ].…”

Physical Interactions Driving the Activation/Inhibition of Calcium/Calmodulin Dependent Protein Kinase II

“…Their most important difference is the length of the linker, which affects the frequency response of CaMKII to Ca 2+ /CaM pulses [12]. In this work, we study the predominant form of CaMKII found in the brain[13, 14], the α isoform, with a β 7 linker connecting the C and N terminals. This linker has been shown to have a reduced kinase activity [15].…”