RESUMEN
Ca2+/calmodulin-dependent protein kinase II (CAMK2) is a key player in synaptic plasticity and memory formation. Mutations in Camk2a or Camk2b cause intellectual disability in humans, and severe plasticity and learning deficits in mice, indicating unique functions for each isoform. However, considering the high homology between CAMK2A and CAMK2B, it is conceivable that for critical functions, one isoform compensates for the absence of the other, and that the full functional spectrum of neuronal CAMK2 remains to be revealed.Here we show that germline as well as adult deletion of both CAMK2 isoforms in male or female mice is lethal. Moreover, Ca2+-dependent activity as well as autonomous activity of CAMK2 is essential for survival. Loss of both CAMK2 isoforms abolished LTP, whereas synaptic transmission remained intact. The double-mutants showed no gross morphological changes of the brain, and in contrast to the long-considered role for CAMK2 in the structural organization of the postsynaptic density (PSD), deletion of both CAMK2 isoforms did not affect the biochemical composition of the PSD. Together, these results reveal an essential role for CAMK2 signaling in early postnatal development as well as the mature brain, and indicate that the full spectrum of CAMK2 requirements cannot be revealed in the single mutants because of partial overlapping functions of CAMK2A and CAMK2B.SIGNIFICANCE STATEMENT CAMK2A and CAMK2B have been studied for over 30 years for their role in neuronal functioning. However, most studies were performed using single knock-out mice. Because the two isoforms show high homology with respect to structure and function, it is likely that some redundancy exists between the two isoforms, meaning that for critical functions CAMK2B compensates for the absence of CAMK2A and vice versa, leaving these functions to uncover. In this study, we generated Camk2a/Camk2b double-mutant mice, and observed that loss of CAMK2, as well as the loss of Ca2+-dependent and Ca2+-independent activity of CAMK2 is lethal. These results indicate that despite 30 years of research the full spectrum of CAMK2 functioning in neurons remains to be unraveled.
Asunto(s)
Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/genética , Neuronas/metabolismo , Animales , Encéfalo/crecimiento & desarrollo , Encéfalo/metabolismo , Encéfalo/fisiología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Femenino , Eliminación de Gen , Mutación de Línea Germinal , Potenciación a Largo Plazo , Masculino , Ratones , Ratones Endogámicos C57BL , Neurogénesis , Neuronas/citología , Neuronas/fisiología , Densidad Postsináptica/metabolismoRESUMEN
Genetic approaches using temporal and brain region-specific restricted gene deletions have provided a wealth of insight in the brain regions and temporal aspects underlying spatial and associative learning. However, for locomotion such extensive studies are still scarce. Previous studies demonstrated that Camk2b(-/-) mice, which lack the ß isoform of Calcium/Calmodulin-dependent protein kinase 2 (CAMK2B), show very severe locomotion deficits. However, where these locomotion deficits originate is unknown. Here we made use of novel Camk2b mutants (Camk2b(f/f) and Camk2b(T287A)), to explore the molecular, temporal and brain region-specific requirements of CAMK2B for locomotion. At the molecular level we found that normal locomotion requires Calcium/Calmodulin mediated activation of CAMK2B, but CAMK2B autonomous activity is largely dispensable. At a systems level, we found that global deletion of Camk2b in the adult mouse causes only mild locomotion deficits, suggesting that the severe locomotion deficits of Camk2b(-/-) mice are largely of developmental origin. However, early onset deletion of Camk2b in cerebellum, striatum or forebrain did not recapitulate the locomotion deficits, suggesting that these deficits cannot be attributed to a single brain area. Taken together, these results provide the first insights into the molecular, temporal and region-specific role of CAMK2B in locomotion.
Asunto(s)
Aprendizaje por Asociación/fisiología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/genética , Calcio/metabolismo , Mutación , Aprendizaje Espacial/fisiología , Animales , Mapeo Encefálico , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/deficiencia , Calmodulina/genética , Calmodulina/metabolismo , Cerebelo/metabolismo , Cerebelo/fisiopatología , Cuerpo Estriado/metabolismo , Cuerpo Estriado/fisiopatología , Femenino , Expresión Génica , Isoenzimas/deficiencia , Isoenzimas/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Prosencéfalo/metabolismo , Prosencéfalo/fisiopatología , Prueba de Desempeño de Rotación con Aceleración ConstanteRESUMEN
UBE2A deficiency syndrome (also known as X-linked intellectual disability type Nascimento) is an intellectual disability syndrome characterized by prominent dysmorphic features, impaired speech and often epilepsy. The syndrome is caused by Xq24 deletions encompassing the UBE2A (HR6A) gene or by intragenic UBE2A mutations. UBE2A encodes an E2 ubiquitin-conjugating enzyme involved in DNA repair and female fertility. A recent study in Drosophila showed that dUBE2A binds to the E3 ligase Parkin, which is required for mitochondrial function and responsible for juvenile Parkinson's disease. In addition, these studies showed impairments in synaptic transmission in dUBE2A mutant flies. However, a causal role of UBE2A in of cognitive deficits has not yet been established. Here, we show that Ube2a knockout mice have a major deficit in spatial learning tasks, whereas other tested phenotypes, including epilepsy and motor coordination, were normal. Results from electrophysiological measurements in the hippocampus showed no deficits in synaptic transmission nor in the ability to induce long-term synaptic potentiation. However, a small but significant deficit was observed in mGLUR-dependent long-term depression, a pathway previously implied in several other mouse models for neurodevelopmental disorders. Our results indicate a causal role of UBE2A in learning and mGLUR-dependent long-term depression, and further indicate that the Ube2a knockout mouse is a good model to study the molecular mechanisms underlying UBE2A deficiency syndrome.
Asunto(s)
Aprendizaje/fisiología , Depresión Sináptica a Largo Plazo/fisiología , Memoria/fisiología , Plasticidad Neuronal/fisiología , Enzimas Ubiquitina-Conjugadoras/fisiología , Animales , Enfermedades Genéticas Ligadas al Cromosoma X/genética , Hipocampo/fisiología , Discapacidad Intelectual/genética , Potenciación a Largo Plazo , Masculino , Ratones , Ratones Noqueados , Mutación , Receptores de Glutamato Metabotrópico/metabolismo , Conducta Social , Transmisión Sináptica/fisiología , Enzimas Ubiquitina-Conjugadoras/deficiencia , Enzimas Ubiquitina-Conjugadoras/genéticaRESUMEN
The α isoform of the calcium/calmodulin-dependent protein kinase II (αCaMKII) has been implicated extensively in molecular and cellular mechanisms underlying spatial and contextual learning in a wide variety of species. Germline deletion of Camk2a leads to severe deficits in spatial and contextual learning in mice. However, the temporal and region-specific requirements for αCaMKII have remained largely unexplored. Here, we generated conditional Camk2a mutants to examine the influence of spatially restricted and temporally controlled expression of αCaMKII. Forebrain-specific deletion of the Camk2a gene resulted in severe deficits in water maze and contextual fear learning, whereas mice with deletion restricted to the cerebellum learned normally. Furthermore, we found that temporally controlled deletion of the Camk2a gene in adult mice is as detrimental as germline deletion for learning and synaptic plasticity. Together, we confirm the requirement for αCaMKII in the forebrain, but not the cerebellum, in spatial and contextual learning. Moreover, we highlight the absolute requirement for intact αCaMKII expression at the time of learning.