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A Phenotyping Regimen for Genetically Modified Mice Used to Study Genes Implicated in Human Diseases of Aging
Published on: July 14, 2016
Genetic and phenotypic analysis of the mouse mutant mh2J, an Ap3d allele caused by IAP element insertion
Prameela Kantheti1, Maria E Diaz, Andrew E Peden
1Mental Health Research Inst., University of Michigan, 205 Zina Pitcher Place, Ann Arbor 48109-0720, USA.
Abstract:
Mocha (mh), a mouse model for Hermansky-Pudlak syndrome (HPS), is characterized by platelet storage pool deficiency, pigment dilution, and deafness as well as neurological abnormalities. The trans-Golgi/endosome adaptor-related complex AP-3 is missing in mh mice owing to a deletion in the gene encoding the delta subunit. Mice mutant for a second allele, mh(2J), are as hyperactive as mh, and display both spike wave absence and generalized tonic clonic seizures, but have less coat color dilution, no hearing loss, and no hypersynchronized EEG. Here we show that the mh(2J) mutation is due to an IAP element insertion in the Ap3d gene leading to a C-terminally truncated protein. Despite correct assembly of the AP-3 complex and localization to the trans-Golgi network and endosomes, AP-3 function in neurons remains impaired. While mh mice show a severe reduction of vesicular zinc (TIMM staining) owing to mislocalization and degradation of the Zinc transporter ZnT-3, the TIMM and ZnT-3 staining patterns in mh(2J) varies, with normal expression in hippocampal mossy fibers, but abnormal patterns in neocortex. These results indicate that the N-terminal portion of the delta subunit is sufficient for AP-3 complex assembly and subcellular localization to the TGN/endosomes, while subsequent function is regulated in part by cell-specific interactions with the C-terminal portion.
Insights
The delta subunit of the AP-3 complex is crucial for neuronal function in Hermansky-Pudlak syndrome (HPS) mouse models. Its C-terminal portion influences zinc transporter regulation and neurological abnormalities.
Area of Science:
- Genetics
- Neuroscience
- Cell Biology
Background:
- Mocha (mh) mice, a model for Hermansky-Pudlak syndrome (HPS), exhibit platelet dysfunction, pigment dilution, deafness, and neurological issues due to a defective AP-3 complex.
- A second allele, mh(2J), shows hyperactivity and seizures but less severe pigment and hearing loss, suggesting distinct functional impacts of the mutation.
Purpose of the Study:
- To investigate the molecular basis of the mh(2J) mutation and its impact on AP-3 complex function in neurons.
- To determine the role of the delta subunit's C-terminal portion in AP-3 complex localization and function, particularly concerning zinc transport.
Main Methods:
- Genetic analysis of the mh(2J) mutation, identifying an IAP element insertion in the Ap3d gene.
- Assessment of AP-3 complex assembly and localization in mh(2J) neurons.
- Analysis of vesicular zinc (TIMM staining) and Zinc transporter ZnT-3 localization in mh and mh(2J) mice.
Main Results:
- The mh(2J) mutation results in a C-terminally truncated delta subunit, yet the AP-3 complex still assembles and localizes to the trans-Golgi network/endosomes.
- Neuronal AP-3 function remains impaired in mh(2J) mice, with altered patterns of vesicular zinc and ZnT-3.
- Unlike mh mice with severe zinc reduction, mh(2J) shows variable ZnT-3 expression, with normal patterns in hippocampal mossy fibers but abnormal patterns in the neocortex.
Conclusions:
- The N-terminal part of the delta subunit is sufficient for AP-3 complex assembly and TGN/endosome localization.
- The C-terminal portion of the delta subunit plays a critical role in regulating AP-3 function in neurons, likely through cell-specific interactions affecting zinc transporter localization.
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