Dapper Antagonist of Catenin-1 Cooperates with Dishevelled-1 during Postsynaptic Development in Mouse Forebrain GABAergic Interneurons

Synaptogenesis has been extensively studied along with dendritic spine development in glutamatergic pyramidal neurons, however synapse development in cortical interneurons, which are largely aspiny, is comparatively less well understood. Dact1, one of 3 paralogous Dact (Dapper/Frodo) family members in mammals, is a scaffold protein implicated in both the Wnt/β-catenin and the Wnt/Planar Cell Polarity pathways. We show here that Dact1 is expressed in immature cortical interneurons. Although Dact1 is first expressed in interneuron precursors during proliferative and migratory stages, constitutive Dact1 mutant mice have no major defects in numbers or migration of these neurons. However, cultured cortical interneurons derived from these mice have reduced numbers of excitatory synapses on their dendrites. We selectively eliminated Dact1 from mouse cortical interneurons using a conditional knock-out strategy with a Dlx-I12b enhancer-Cre allele, and thereby demonstrate a cell-autonomous role for Dact1 during postsynaptic development. Confirming this cell-autonomous role, we show that synapse numbers in Dact1 deficient cortical interneurons are rescued by virally-mediated re-expression of Dact1 specifically targeted to these cells. Synapse numbers in these neurons are also rescued by similarly targeted expression of the Dact1 binding partner Dishevelled-1, and partially rescued by expression of Disrupted in Schizophrenia-1, a synaptic protein genetically implicated in susceptibility to several major mental illnesses. In sum, our results support a novel cell-autonomous postsynaptic role for Dact1, in cooperation with Dishevelled-1 and possibly Disrupted in Schizophrenia-1, in the formation of synapses on cortical interneuron dendrites.     

The effects of date of planting on field establishment of serotinous cape Proteaceae

Season of fire have marked effects on the germination and establishment of serotinous shrubs of the family Proteaceae in fynbos vegetation. To investigate reasons for this, we simulated the effects of different fire seasons by planting seeds into cleared fynbos and then followed their progress. Four species of Proteaceae were planted monthly at four sites over two and a half years. Exclosures were used to exclude rodent seed predators. Germination was confined largely to the three winter months (June–Aug.). Seeds planted from January–June had higher germination than those planted in the second half of the year. Higher levels of regeneration noted after fires in the first half of the year, were previously hypothesised to be results of predation. However, we obtained similar results despite the exclusion of seed predators. Monthly minimum temperature was strongly correlated with germination percentage but monthly rainfall was not. Loss of seed viability may be important, in determining post-fire seedling densities. Differential seedling mortality of earlier and late germinants appears to be unimportant in determining establishment levels. Our results nevertheless support the current practice of restricting management fires in fynbos to the summer-autumn period.     

Effects of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea on the Cell Cycle in Euglena gracilis

The cell cycle of the photosynthetic unicellular alga Euglena gracilis growing in phototrophic medium is regulated by light. To investigate the relationship of this cell cycle response to light stimulated photosynthesis, we have tested the effect of the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on Euglena cell cycle transit. While DCMU does not block light stimulated cells from entering the S phase of the cell cycle, it does inhibit the transit through G₂/M. The specificity of this response and its relationship to photosynthesis was studied by looking at the effect of DCMU on dark grown wild-type cells, and on two bleached variants of Euglena (W₃BUL and W₁₀BSmL) that lack chloroplasts. The drug does block G₂/M in these cells, but not entrance into the cell cycle. Our studies show that entrance of cells into the cell cycle from a quiescent state does not require active photosynthesis, and that DCMU has effects on G₂/M transit that are independent of the photosynthetic capacity of the cells.     

Effects of lignin on the anaerobic degradation of (ligno) cellulosic wastes by rumen microorganisms

Summary There appeared to be a clear correlation between the lignin content (% of TS) of several waste and natural materials and their degradability by rumen microorganisms. Materials with lignin contents higher than 25% were not degraded within 72 h. The effects of Kraft pine lignin and some lignin monomers on filter paper degradation, methane production and CMCase activity were tested. Testing these compounds in concentrations comparable to natural conditions showed minor effects. At higher concentrations p-coumaric acid strongly inhibited cellulose degradation and methane production in batch cultures. Influence of lignin compounds on degradation is discussed in relation to structural effects and enzyme or growth inhibition.     

Calmodulin Acts as an intermediary for the effects of calcium on gap junctions from crayfish lateral axons

Summary Lateral axons from the abdominal nerve cord of cray-fish were internally perfused with the calcium receptor calmodulin (CaM) in solutions with low (pCa>7.0) or high (pCa 5.5) calcium concentrations and studied electrophysiologically and morphologically. Results from these experiments show that when the internal solution contains calcium-activated calmodulin (Ca²⁺-CaM) the junctional resistance between the axons increases from control values of about 60 to 500–600 k in 60 min. In contrast, axons perfused with calmodulin in low calcium solutions maintain their junctional resistance at control levels during the 60-min perfusion. Similar results are obtained when only one or both coupled axons are perfused.The morphological study shows that in the perfused axons the axoplasmic organelles are replaced or grossly perturbed by the perfusion solution up to the region of the synapses. Additionally, in axons perfused with Ca²⁺-CaM there are regions where the synaptic gap between the membranes decreases from a control 4–6 to 2–3 nm. Both electrophysiological and morphological results can be interpreted as indicating that calcium-activated calmodulin acts directly on the junctional channels to induce their closure.     

Lowering of pH does not directly affect the junctional resistance of crayfish lateral axons

Summary The effect of pH was tested on the junction between crayfish lateral axons. By means of a glass capillary inserted into one of the axons, one side of the nunction was perfused with solutions of known pH while the junctional resistance,R _j, was monitored. Integrity of the gap junction was checked electron microscopically.R _j remained unchanged when the pH of the perfusate was lowered from 7.1 to 6.0. However, when the pH of the unperfused side of the junction was lowered by substituting acetate for chloride in the external solution,R _j rose, attesting to the integrity of the junction and its capacity to uncouple in the perfused state. We suggest that H⁺ does not affect the junctional channels directly, but acts through an intermediary which is inactivated or removed by the perfusion.     

Temporal Patterns of Reported Single-Vehicle Car and Truck Accidents in Texas, U.S.A. During 1980-1983

Reported single car and truck accidents due specifically to driver 'fatigue' for the 4-year span of 1980-1983 were analyzed for 24-hr, 7-d and 1-yr patterns. Three types of data were examined: (1) accidents in rural Texas, (2) accidents only in San Antonio, the fourth largest city in Texas and (3) accident ratio (number of accidents per time interval divided by traffic volume for the interval) in this city.

A statistically significant seasonal variation of relatively low amplitude with peaks in May and July was detected only for accidents in rural areas. High-amplitude periodicities of 7 d were evident in all the data sets, with a peak on the weekend. A very prominent 24-hr pattern was detected as well, with the acrophase determined by single cosinor around 0300. A slight secondary peak in accidents, around 1500, was evident in the data from the rural areas. This secondary peak represented a 12-hr rhythm in addition to the 24-hr. Overall, features of the temporal patterns in accidents over 24 hr and over the year in urban and rural areas differed only slightly. Accident ratios yielded results similar to accident frequencies. However, with regard to the rural data, the shape of the 24-hr temporal pattern varied with driver age; older drivers exhibited a flatter curve with a more pronounced afternoon rather than early morning (around 0300) peak.