An Ancient Duplication of Exon 5 in the Snap25 Gene Is Required for Complex Neuronal Development/Function

Alternative splicing is an evolutionary innovation to create functionally diverse proteins from a limited number of genes. SNAP-25 plays a central role in neuroexocytosis by bridging synaptic vesicles to the plasma membrane during regulated exocytosis. The SNAP-25 polypeptide is encoded by a single copy gene, but in higher vertebrates a duplication of exon 5 has resulted in two mutually exclusive splice variants, SNAP-25a and SNAP-25b. To address a potential physiological difference between the two SNAP-25 proteins, we generated gene targeted SNAP-25b deficient mouse mutants by replacing the SNAP-25b specific exon with a second SNAP-25a equivalent. Elimination of SNAP-25b expression resulted in developmental defects, spontaneous seizures, and impaired short-term synaptic plasticity. In adult mutants, morphological changes in hippocampus and drastically altered neuropeptide expression were accompanied by severe impairment of spatial learning. We conclude that the ancient exon duplication in the Snap25 gene provides additional SNAP-25-function required for complex neuronal processes in higher eukaryotes

Influenza A virus infection and NMDA receptor function : A behavioral and molecular study of relevance for schizophrenia

Schizophrenia is a neuropsychiatric disorder characterized by positive and negative symptoms, as well as cognitive dysfunctions. There is no single cause of schizophrenia, instead complex combinations of genetic and environmental factors may contribute to the disorder, including exposure to viral infections or other environmental insults during early life. Discoveries during the last 30 years have provided increasing evidence for a glutamatergic hypofunction in schizophrenia. This hypothesis arose from the finding that non-competitive N-methyl-d-aspartate (NMDA) receptor antagonists, such as ketamine and phencyclidine (PCP) can reproduce schizophrenia-like symptoms including cognitive dysfunctions in man. This observation, has led to a search for schizophrenia-related animal models based on NMDA-receptor blockade. The main aim of these studies was to investigate if exposure to influenza A virus during early life can result in cognitive dysfunctions during adult life. In addition, to allow studies on the potential role of NMDA receptor systems for cognition, a novel NMDA receptor hypofunction model was developed. Both acute and repeated treatment with NMDA receptor antagonists is known to produce a dose-related spectrum of motor dysfunctions that interfere with cognitive performance in rodents. For this reason, PCP was examined in a dose-dependent study to establish the dose-range of cognitive impairments versus motor side effects. Repeated administration of the 0.5 mg/kg dose of PCP impaired spatial learning and long-term memory without affecting non-spatial learning. The PCP-induced impairments in learning and memory were prevented by concomitant treatment with the atypical antipsychotic drug clozapine (0.5 mg/kg), but not with the typical antipsychotic haloperidol (0.05 mg/kg). To avoid testing with the drug on board , the effects of repeated administration of PCP on cognitive and social behavior were examined 24 h after the final dose of PCP. In addition, this study examined the effect of such treatment on the expression of two genes involved in neuronal plasticity and learning. Repeated doses of PCP (1 and 2 mg/kg) produced long-term impairments in spatial learning and working memory performance in the water maze task, without any apparent sensorimotor deficits. Furthermore, mice treated with 2 mg/kg of PCP spent less time in active social interaction, and showed increased non-social and aggressive behaviors. These behavioral effects were associated with altered expression of the genes encoding Arc and spinophilin. The alterations in Arc transcripts were observed in areas associated with spatial learning such as the CA1 region of the hippocampus and in the retrosplenial cortex. To examine if exposure to a maternal infection affects gene expression in the offspring, pregnant C57BL/6 mice were instilled intranasally with influenza A/WSN/33 virus on day 14 of gestation. Differential gene expression in the brains of the offspring could be detected at postnatal days 90 and 280, but not earlier. Thus, a maternal influenza A virus infection can give rise to alterations in gene expression that become apparent only after a considerable period of latency. A subsequent study examined the effects of an influenza A virus infection in 3-4-day old C57BL/6 or immunodeficient (Tap1-/-) mice. This infection led to transient changes in expression of several genes associated with schizophrenia in C57BL/6 mice while Tap1-/- mice exhibited more enduring changes. Whereas infected C57BL/6 mice were deficient only in the long-term memory task, infected Tap1-/- mice showed deficits in working memory performance. The olfactory tract provides an interesting route of invasion for studies of viruses to the brain. Therefore, mice were injected with influenza A virus into the olfactory bulbs at 5-6 weeks of age. Sixteen to eighteen weeks after the infection these mice showed impaired spatial learning and reduced anxiety-like behavior. Moreover, genes encoding synaptic regulatory proteins were differentially expressed in the amygdala, the hypothalamus and the cerebellum in these mice. Finally, to link early life virus infection to possible changes in NMDA receptor function, a subchronic dose of PCP (2 mg/kg) was given to control mice and mice infected on day 3. The marked impairment in cognition by subchronic PCP was confirmed in control mice. Virus infected mice tended to be more susceptible to these PCP-induced deficits in cognition and showed a clear difference in the pattern of motor activity compared to control mice. In conclusion this thesis shows that (i) repeated low dose of PCP impairs cognitive functions and is reversed by clozapine; (ii) repeated administration of PCP can produce long-term effects on cognition, social behavior and gene expression after termination of the treatment; (iii) influenza A virus infections can cause alterations in the expression of (schizophrenia-associated) genes and behavior. The effect of the infection appears to be influenced by the timing and route of infection; and (iv) mice infected with a virus during early life appear more susceptible to repeated PCP treatment in adulthood

GEOLOGY OF THE HOMO-BEARING PLEISTOCENE DANDIERO BASIN (BUIA REGION, ERITREAN DANAKIL DEPRESSION)

This paper deals with the geological context of the northernmost site in the East Africa Rift system which has yielded Homo erectus-like remains. They are dated ca. 1 Ma and have been found in the deltaic deposits of the Alat Formation belonging to the Dandiero group. This newly defined group crops out extensively in an elongated belt from the Gulf of Zula to the North to the Garsat area to the south. In the Buia-Dandiero area it ranges in age from the Early to the Middle Pleistocene, and incorporates six formations, from bottom up: the fluvial Bukra Sand and Gravel, the deltaic and lacustrine Alat Formation, fluvial Wara Sand and Gravel, the lacustrine Goreya Formation, the fluvio-deltaic Aro Sand and alluvial Addai Fanglomerate. This succession is bounded by two major unconformities, which separate it from the Neoproterozoic basement and from the overlaying Boulder Beds fanglomerate, and has been designated the Maebele Synthem. The latter is the result of two lacustrine transgression and regressions evidenced by two depositional sequences. The unconformities bounding the Maebele Synthem are related to the tectonic history of the basin fill and its substrate. The development of the two sequences was, instead, mainly controlled by lake level fluctuations and, hence, by climatic variations connected with the weakening and strengthening of the monsoons in the northwestern Indian ocean. The environment where the Buia Homo lived was a savannah with some scattered water pools. This environment probably extended farther north along the western coastal plain of the Red Sea, and was a preferential pathway for the dispersal of the hominids from East Africa toward Eurasia.

Cognitive abilities assessed in the Npas4 line.

<p>WT (n = 21), HET (n = 22), and KO (n = 10) mice were tested in the spontaneous alternation test to assess their working memory. (A) The total number of arm entries was not affected by the genotype. (B) The percent of alternation in the Y-maze was significantly above chance level (50%) in WT and HET mice but not in KO mice. *** p<0.001.</p

Cognitive abilities assessed in the Npas4 line.

<p>(A) During the novel object recognition test WT mice (n = 13) performed normally and sniffed a novel object longer than a familiar one; HET mice (n = 15) and KO mice (n = 3) performed poorly and did not show a preference for a novel object over a familiar one. (B-E) c-Fos expression was measured after the object recognition test in Npas4 WT (n = 3), HET (n = 3), and KO (n = 3) mice. The total number of c-Fos positive cells was counted using the stereological method in the CA1, CA2, CA3 regions and the dentate gyrus (DG) of the hippocampus. Pictures are representative pictures of c-Fos staining in the hippocampus. The black arrows represent c-Fos positive cells. The scale bar on the picture represents 100 µm. *** p<0.001; **p<0.01; *p<0.05; T p = 0.097.</p

Anxiety and locomotor activity assessed in the Npas4 line.

<p>(A) Percent of time spent in the center of the open-field: no difference was observed between WT (n = 22), HET (n = 22), and KO (n = 8) mice (B) Total distance traveled in the open-field: KO mice moved a longer distance than the WT. ** p<0.01.</p