AP3 in Neurological Disorders

Burmeister, Margit

Abstract

The P.I. has recently identified the mutant gene in mocha mice as the delta subunit of the adapter-related complex AP-3. They have also found that the ZnT-3 transporter is not transported correctly to synaptic vesicles, resulting in a lack of zinc in cortex and hippocampus. In this application, the P.I. proposes to genetically map all subunits of the AP-3 complex to determine if other mutants with a similar phenotype are caused by mutations in these AP-3 subunit genes, and test for interaction between mocha locus and pale-ear, the mouse homologue of HPS, the gene most commonly mutated in human Hermansky-Pudlak syndrome (HPS). They will focus on the neurological phenotype of mocha, and determine if mocha may be a mouse model for epilepsy, ADHD, autism or other neurological disorders. Mocha mutant mice have an HPS-like phenotype as well as neurological deficits (seizures, hyperactivity, spike-wave discharges, a hypersynchronized electrocortigram, increased auditory gating). In contrast, pearl mice have HPS but none of these neurological phenotypes, which they postulate is because pearl mice miss the non-neuronal form of the beta subunit, Ap3b1, but not the neuronal form of AP-3 beta, Ap3b2, whereas the delta subunit mutated in mocha is ubiquitously expressed. Dr. Burmeister postulates that inactivation of the neuronal form of AP-3 beta will result in a mouse with the neurological defects of mocha without the HPS-like phenotypes and higher fertility and viability than mocha mice. They will prepare a LoxP construct to knock out Ap3b2 in such a way that they can not only generate a complete knockout in ES cells, but also, by mating to mice in which Cre is under region-specific promoters, mice in which the AP-3 complex is missing only in specific brain regions. The P.I. will characterize the behavior of mocha, mh-2J, ZnT-3 deficient mice as well as the proposed knockout mice for the nature of hyperactivity (is it generally more active, has increased startle, or stereotypic behavior), seizure propensity, anxiety, learning and memory and electrophysiological parameters. To determine if AP3B2 plays a role in human neurological disorders, Dr. Burmeister will isolate and characterize the human AP3B2 gene and search for mutations or polymorphisms that may be present in the normal population or in patients. Given the mocha phenotype, it is anticipated that this gene may be involved in human neurological disorders characterized by increased seizure frequency and hyperactivity (e.g. autism, OCD, ADHD and epilepsy). Such polymorphisms will be made available for the scientific community to test as a candidate gene for other neurological or psychiatric disorders if justified by the results of the behavior tests.