Progressive Purkinje Cell Degeneration in tambaleante Mutant Mice Is a Consequence of a Missense Mutation in HERC1 E3 Ubiquitin Ligase

The HERC gene family encodes proteins with two characteristic domains: HECT and RCC1-like. Proteins with HECT domains have been described to function as ubiquitin ligases, and those that contain RCC1-like domains have been reported to function as GTPases regulators. These two activities are essential in a number of important cellular processes such as cell cycle, cell signaling, and membrane trafficking. Mutations affecting these domains have been found associated with retinitis pigmentosa, amyotrophic lateral sclerosis, and cancer. In humans, six HERC genes have been reported which encode two subgroups of HERC proteins: large (HERC1-2) and small (HERC3-6). The giant HERC1 protein was the first to be identified. It has been involved in membrane trafficking and cell proliferation/growth through its interactions with clathrin, M2-pyruvate kinase, and TSC2 proteins. Mutations affecting other members of the HERC family have been found to be associated with sterility and growth retardation. Here, we report the characterization of a recessive mutation named tambaleante, which causes progressive Purkinje cell degeneration leading to severe ataxia with reduced growth and lifespan in homozygous mice aged over two months. We mapped this mutation in mouse chromosome 9 and then performed positional cloning. We found a G⇔A transition at position 1448, causing a Gly to Glu substitution (Gly483Glu) in the highly conserved N-terminal RCC1-like domain of the HERC1 protein. Successful transgenic rescue, with either a mouse BAC containing the normal copy of Herc1 or with the human HERC1 cDNA, validated our findings. Histological and biochemical studies revealed extensive autophagy associated with an increase of the mutant protein level and a decrease of mTOR activity. Our observations concerning this first mutation in the Herc1 gene contribute to the functional annotation of the encoded E3 ubiquitin ligase and underline the crucial and unexpected role of this protein in Purkinje cell physiology

Identification and structural characterization of FYVE domain-containing proteins of Arabidopsis thaliana

<p>Abstract</p> <p>Background</p> <p>FYVE domains have emerged as membrane-targeting domains highly specific for phosphatidylinositol 3-phosphate (PtdIns(3)<it>P</it>). They are predominantly found in proteins involved in various trafficking pathways. Although FYVE domains may function as individual modules, dimers or in partnership with other proteins, structurally, all FYVE domains share a fold comprising two small characteristic double-stranded β-sheets, and a C-terminal α-helix, which houses eight conserved Zn²⁺ion-binding cysteines. To date, the structural, biochemical, and biophysical mechanisms for subcellular targeting of FYVE domains for proteins from various model organisms have been worked out but plant FYVE domains remain noticeably under-investigated.</p> <p>Results</p> <p>We carried out an extensive examination of all <it>Arabidopsis </it>FYVE domains, including their identification, classification, molecular modeling and biophysical characterization using computational approaches. Our classification of fifteen <it>Arabidopsis </it>FYVE proteins at the outset reveals unique domain architectures for FYVE containing proteins, which are not paralleled in other organisms. Detailed sequence analysis and biophysical characterization of the structural models are used to predict membrane interaction mechanisms previously described for other FYVE domains and their subtle variations as well as novel mechanisms that seem to be specific to plants.</p> <p>Conclusions</p> <p>Our study contributes to the understanding of the molecular basis of FYVE-based membrane targeting in plants on a genomic scale. The results show that FYVE domain containing proteins in plants have evolved to incorporate significant differences from those in other organisms implying that they play a unique role in plant signaling pathways and/or play similar/parallel roles in signaling to other organisms but use different protein players/signaling mechanisms.</p

The HERC2 ubiquitin ligase is essential for embryonic development and regulates motor coordination

A mutation in the HERC2 gene has been linked to a severe neurodevelopmental disorder with similarities to the Angelman syndrome. This gene codifies a protein with ubiquitin ligase activity that regulates the activity of tumor protein p53 and is involved in important cellular processes such as DNA repair, cell cycle, cancer, and iron metabolism. Despite the critical role of HERC2 in these physiological and pathological processes, little is known about its relevance in vivo. Here, we described a mouse with targeted inactivation of the Herc2 gene. Homozygous mice were not viable. Distinct from other ubiquitin ligases that interact with p53, such as MDM2 or MDM4, p53 depletion did not rescue the lethality of homozygous mice. The HERC2 protein levels were reduced by approximately one-half in heterozygous mice. Consequently, HERC2 activities, including ubiquitin ligase and stimulation of p53 activity, were lower in heterozygous mice. A decrease in HERC2 activities was also observed in human skin fibroblasts from individuals with an Angelman-like syndrome that express an unstable mutant protein of HERC2. Behavioural analysis of heterozygous mice identified an impaired motor synchronization with normal neuromuscular function. This effect was not observed in p53 knockout mice, indicating that a mechanism independent of p53 activity is involved. Morphological analysis showed the presence of HERC2 in Purkinje cells and a specific loss of these neurons in the cerebella of heterozygous mice. In these animals, an increase of autophagosomes and lysosomes was observed. Our findings establish a crucial role of HERC2 in embryonic development and motor coordination

The HERC2 ubiquitin ligase is essential for embryonic development and regulates motor coordination

A mutation in the HERC2 gene has been linked to a severe neurodevelopmental disorder with similarities to the Angelman syndrome. This gene codifies a protein with ubiquitin ligase activity that regulates the activity of tumor protein p53 and is involved in important cellular processes such as DNA repair, cell cycle, cancer, and iron metabolism. Despite the critical role of HERC2 in these physiological and pathological processes, little is known about its relevance in vivo. Here, we described a mouse with targeted inactivation of the Herc2 gene. Homozygous mice were not viable. Distinct from other ubiquitin ligases that interact with p53, such as MDM2 or MDM4, p53 depletion did not rescue the lethality of homozygous mice. The HERC2 protein levels were reduced by approximately one-half in heterozygous mice. Consequently, HERC2 activities, including ubiquitin ligase and stimulation of p53 activity, were lower in heterozygous mice. A decrease in HERC2 activities was also observed in human skin fibroblasts from individuals with an Angelman-like syndrome that express an unstable mutant protein of HERC2. Behavioural analysis of heterozygous mice identified an impaired motor synchronization with normal neuromuscular function. This effect was not observed in p53 knockout mice, indicating that a mechanism independent of p53 activity is involved. Morphological analysis showed the presence of HERC2 in Purkinje cells and a specific loss of these neurons in the cerebella of heterozygous mice. In these animals, an increase of autophagosomes and lysosomes was observed. Our findings establish a crucial role of HERC2 in embryonic development and motor coordination

The HERC2 ubiquitin ligase is essential for embryonic development and regulates motor coordination

A mutation in the HERC2 gene has been linked to a severe neurodevelopmental disorder with similarities to the Angelman syndrome. This gene codifies a protein with ubiquitin ligase activity that regulates the activity of tumor protein p53 and is involved in important cellular processes such as DNA repair, cell cycle, cancer, and iron metabolism. Despite the critical role of HERC2 in these physiological and pathological processes, little is known about its relevance in vivo. Here, we described a mouse with targeted inactivation of the Herc2 gene. Homozygous mice were not viable. Distinct from other ubiquitin ligases that interact with p53, such as MDM2 or MDM4, p53 depletion did not rescue the lethality of homozygous mice. The HERC2 protein levels were reduced by approximately one-half in heterozygous mice. Consequently, HERC2 activities, including ubiquitin ligase and stimulation of p53 activity, were lower in heterozygous mice. A decrease in HERC2 activities was also observed in human skin fibroblasts from individuals with an Angelman-like syndrome that express an unstable mutant protein of HERC2. Behavioural analysis of heterozygous mice identified an impaired motor synchronization with normal neuromuscular function. This effect was not observed in p53 knockout mice, indicating that a mechanism independent of p53 activity is involved. Morphological analysis showed the presence of HERC2 in Purkinje cells and a specific loss of these neurons in the cerebella of heterozygous mice. In these animals, an increase of autophagosomes and lysosomes was observed. Our findings establish a crucial role of HERC2 in embryonic development and motor coordination

The HERC2 ubiquitin ligase is essential for embryonic development and regulates motor coordination

A mutation in the HERC2 gene has been linked to a severe neurodevelopmental disorder with similarities to the Angelman syndrome. This gene codifies a protein with ubiquitin ligase activity that regulates the activity of tumor protein p53 and is involved in important cellular processes such as DNA repair, cell cycle, cancer, and iron metabolism. Despite the critical role of HERC2 in these physiological and pathological processes, little is known about its relevance in vivo. Here, we described a mouse with targeted inactivation of the Herc2 gene. Homozygous mice were not viable. Distinct from other ubiquitin ligases that interact with p53, such as MDM2 or MDM4, p53 depletion did not rescue the lethality of homozygous mice. The HERC2 protein levels were reduced by approximately one-half in heterozygous mice. Consequently, HERC2 activities, including ubiquitin ligase and stimulation of p53 activity, were lower in heterozygous mice. A decrease in HERC2 activities was also observed in human skin fibroblasts from individuals with an Angelman-like syndrome that express an unstable mutant protein of HERC2. Behavioural analysis of heterozygous mice identified an impaired motor synchronization with normal neuromuscular function. This effect was not observed in p53 knockout mice, indicating that a mechanism independent of p53 activity is involved. Morphological analysis showed the presence of HERC2 in Purkinje cells and a specific loss of these neurons in the cerebella of heterozygous mice. In these animals, an increase of autophagosomes and lysosomes was observed. Our findings establish a crucial role of HERC2 in embryonic development and motor coordination