The development of the adult central nervous system of Drosophila requires a precise and reproducible pattern of neuroblast proliferation during postembryonic neurogenesis. We show here that mutations in the minibrain (mnb) gene cause an abnormal spacing of neuroblasts in the outer proliferation center (opc) of larval brain, with the implication that mnb opc neuroblasts produce less neuronal progeny than do wild type. As a consequence, the adult mnb brain exhibits a specific and marked size reduction of the optic lobes and central brain hemispheres. The insufficient number of distinct neurons in mnb brains is correlated with specific abnormalities in visual and olfactory behavior. The mnb gene encodes a novel, cell type-specific serine-threonine protein kinase family that is expressed and required in distinct neuroblast proliferation centers during postembryonic neurogenesis. The mnb kinases share extensive sequence similarities with kinases involved in the regulation of cell division.

No abstract

Volado is a new memory mutant of Drosophila. The locus encodes two isoforms of a new alpha-integrin, a molecule that dynamically mediates cell adhesion and signal transduction. The Volado gene is expressed preferentially in mushroom body cells, which are neurons known to mediate olfactory learning in insects. Volado proteins are concentrated in the mushroom body neuropil, brain areas that contain mushroom body processes in synaptic contact with other neurons. Volado mutants display impaired olfactory memories within 3 min of training, indicating that the integrin is required for short-term memory processes. Conditional expression of a Volado transgene during adulthood rescues the memory impairment. This rescue of memory is reversible, fading over time along with expression of the transgene. Thus the Volado integrin is essential for the physiological processes underlying memory. We propose a model in which integrins act as dynamic regulators of synapse structure or the signalling events underlying short-term memory formation.

Mutations in the gene encoding alpha-synuclein (asyn) causes autosomal-dominant, in the parkin gene autosomal-recessive forms of Parkinson's disease (PD). The pathophysiology of PD is poorly understood, even though published evidence suggests a role for mitochondria in the pathogenesis. To gain insight into the influence of asyn and parkin on mitochondrial integrity and function, we have generated several mono-mutant mouse lines expressing doubly mutated human asyn (hm(2)asyn) under the control of two different promoters, or a targeted deletion of Parkin (Parkin-Exon3-knockout). Both mouse lines were crossed to generate the double-mutant. Here we compare the ultrastructure and functional properties of mitochondria in the substantia nigra (SN), the striatum, the cerebral cortex (Cx) and skeletal muscle of young (2-3 months) and aged (12-14 months) mono- and double-mutants mice. We observed severe genotype-, age- and region-dependent morphological alterations of mitochondria in neuronal somata. The number of structurally altered mitochondria was significantly increased in the SN of both double-mutants and in the Cx of one mono- and one double-mutant line. These alterations coincided with a reduced complex I capacity in the SN, but were neither accompanied by alterations in the number or the size of the mitochondria nor by leakage of cytochrome c, Smac/DIABLO or Omi/HtrA2. None of the transgenic animals developed any gross histopathological abnormalities or overt motor disabilities. Together our results provide compelling evidence that (i) both, asyn and parkin are relevant for mitochondrial integrity, (ii) the influence of these proteins on mitochondria are age- and tissue-specific and (iii) changes of mitochondrial morphology do not inevitably cause functional impairments.

Mutations in the parkin gene are the major cause of early-onset familial Parkinson's disease (PD). We previously reported the generation and analysis of a knockout mouse carrying a deletion of exon 3 in the parkin gene. F1 hybrid pa+/- mice were backcrossed to wild-type C57Bl/6 for three more generations to establish a pa-/-(F4) mouse line. The appearance of tyrosine hydroxylase-positive neurons was normal in young and aged pa-/- (F4) animals. Loss of parkin function in mice did not enhance vulnerability of dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity. However, the pa-/- (F4) mice displayed impaired exploration and habituation to a new environment and exhibited thigmotaxis behaviour in the open field and Morris water maze. Abnormal anxiety-related behaviour of pa-/- (F4) mice was also observed in the light/dark exploration test paradigm. Dopamine metabolism was enhanced in the striatum of pa-/- (F4) mice, as revealed by increased homovanillic acid (HVA) content and a reduced ratio of dihydroxyphenylacetic acid (DOPAC)/HVA. The alterations found in the dopaminergic system could be responsible for the behavioural impairments of pa-/- (F4) mice. Consistent with a recent observation of cognitive dysfunction in parkin-linked patients with PD, our findings provide evidence of a physiological role of parkin in non-motor behaviour, possibly representing a disease stage that precedes dopaminergic neuron loss.

Nineteen GABA A receptor (GABA A R) subunits are known in mammals with only a restricted number of functionally identified native combinations. The physiological role of ␤1-subunit-containing GABA A Rs is unknown. Here we report the discovery of a new structural class of GABA A R positive modulators with unique ␤1-subunit selectivity: fragrant dioxane derivatives (FDD). At heterologously expressed ␣1␤x␥2L (x-for 1,2,3) GABA A R FDD were 6 times more potent at ␤1-versus ␤2-and ␤3-containing receptors. Serine at position 265 was essential for the high sensitivity of the ␤1-subunit to FDD and the ␤1N286W mutation nearly abolished modulation; vice versa the mutation ␤3N265S shifted FDD sensitivity toward the ␤1-type. In posterior hypothalamic neurons controlling wakefulness GABA-mediated whole-cell responses and GABAergic synaptic currents were highly sensitive to FDD, in contrast to ␤1-negative cerebellar Purkinje neurons. Immunostaining for the ␤1-subunit and the potency of FDD to modulate GABA responses in cultured hypothalamic neurons was drastically diminished by ␤1-siRNA treatment. In conclusion, with the help of FDDs we reveal a functional expression of ␤1-containing GABA A Rs in the hypothalamus, offering a new tool for studies on the functional diversity of native GABA A Rs. ␥-Aminobutyric acid (GABA),4 the major inhibitory neurotransmitter in the brain, mediates inhibition via GABA A receptors (GABA A R), heteropentameric proteins constructed from subunits derived from several related gene families with six ␣-, three ␤-, three ␥-, one ␦-, one ⑀-, one -, and one -subunit in mammals. In addition 3 rho ()-subunits contribute to what have been called "GABA C receptors" (1). According to the current model of the GABA A R structure the GABA-binding pocket is formed at the ␣/␤-subunit interface, whereas the benzodiazepine (BZ)-binding pocket is located at the ␣/␥ interface (2) with the subunits arranged pseudo-symmetrically around the ion channel in the sequence ␥-␤-␣-␤-␣ anticlockwise when viewed from the synaptic cleft (3).Functional receptor compositions are restricted in their number and delineated on the basis of several criteria such as (i) capability of selected subunits to form a heteropentamer with defined pharmacological properties, (ii) a similar pharmacological fingerprint must be found in native receptors, and (iii) immunohistochemical co-localization of these subunits must be demonstrated at synaptic or extrasynaptic sites (1). Only few subunit combinations are currently accepted as "identified" native GABA A R subtypes with ␤1-containing receptors not among them (1) mainly because subunit-selective pharmacological tools are missing.In total, the GABA A R incorporates more than ten distinct modulatory binding sites targeted by anticonvulsive, antiepileptic, sedative, hypnotic, and anxiolytic compounds belonging to chemically different structural classes (4 -7) with some of them showing receptor type-specific actions. Benzodiazepine (BZ)-site agonists discriminate ␥2-containing GABA A Rs from recombi...

No abstract

No abstract