Diel variability in catch rate of juvenile flatfish on two small nursery grounds (Port Erin Bay, Isle of Man and Porto Pirn Bay, Faial, Azores)

Variation in beach seine catches was examined in two juvenile flatfish populations (Port Erin, Isle of Man and Porto Pirn, Azores) to determine the importance of diel cycles while controlling for tidal rhythmicity. At Port Erin sampling was undertaken at each low water on consecutive days over a 2-week period in May/June and September 1991. There was no periodicity in the catches of plaice ( Pleuronectes platessa ) in May/June, but in September catches were higher at night. Other flatfish species ( Limanda limanda, Pleuronectes flesus, Scophthalmus maximus and S. rhombus ) sampled at Port Erin were nocturnal. At Porto Pirn, Azores, fish were sampled over 24 h each month from July 1989 to June 1990 and at each low water over a 2-week period in July 1991. The only flatfish species present was Bothuspodas , which had a diurnal pattern in catches over a 1-year period. Sampling at low water in July gave high catches at both midnight and midday.     

Allozyme differentiation within and between red drum (Sciaenops ocellatus) from the Gulf of Mexico and Atlantic Ocean

Nine polymorphic nuclear-gene (allozyme) loci were surveyed among 491 red drum ( Sciaenops ocellatus ) sampled in 1988 and 1989 from nearshore localities in the northern Gulf of Mexico (Gulf) and the Atlantic coast of the southeastern United States (Atlantic). Data were combined with those from a previous study to generate a data set of 762 individuals representing 11 sample localities in the Gulf and 175 individuals representing five sample localities in the Atlantic. The combined data set included individuals from the 1986 and 1987 year classes and permitted rigorous testing of both temporal and spatial genetic heterogeneity. Average heterozygosity-per-locus values (estimated using 33 assumed monomorphic loci) were 0·048 (Gulf red drum) and 0·046 (Atlantic red drum). Tests of heterogeneity in allele frequencies between year classes at individual localities and across regions (Gulf and Atlantic) were non-significant. Tests of spatial (geographic) heterogeneity indicated that red drum are weakly subdivided: genetically-differentiated subpopulations occur in the northern Gulf and along the south-eastern Atlantic coast. Genetic data were consistent with the hypothesis that red drum within the Gulf and along the Atlantic coast comprise singie subpopulalions. Genetic differences between Gulf and Atlantic red drum seem likeiy to stem from historical or recent interactions between dispersal and impediments to gene flow.     

Keepers of maize in Chiapas,Mexico

This study concerns the knowledge and selection of biological diversity of maize (Zea mays) within its center of domestication in Mesoamerica. Maize farmers in central Chiapas of Southern México keep local varieties (landraces) belonging to six races and four race mixtures. Fifteen local varieties are recognized. In spite of widespread adoption of a modern, high yielding variety, maize farmers continue to select local varieties for specific soils and because of agronomic and use criteria. Farmers maintain maize varieties primarily through seed selection. Spatial and temporal separation do not seem sufficient to maintain varieties. The management of improved varieties can lead from a uniform population to a heterogeneous one as hybridization with local maize populations occurs.     

Contrasting rates of nucleotide substitution in the X-Linked and Y-Linked zinc finger genes

We have sequenced the entire exon (1,180 bp) encoding the zinc finger domain of the X-linked and Y-linked zinc finger genes (ZFX and ZFY, respectively) in the orangutan, the baboon, the squirrel monkey, and the rat; a total of 9,442 by were sequenced. The ratio of the rates of synonymous substitution in the ZFY and ZFX genes is estimated to be 2.1 in primates. This is close to the ratio of 2.3 estimated from primate ZFY and ZFX intron sequences and supports the view that the male-to-female ratio of mutation rate in humans is considerably higher than 1 but not extremely large. The ratio of synonymous substitution rates in ZFY and ZFX is estimated to be 1.3 in the rat lineage but 4.2 in the mouse lineage. The former is close to the estimate (1.4) from introns. The much higher ratio in the mouse lineage (not statistically significant) might have arisen from relaxation of selective constraints. The synonymous divergence between mouse and rat ZFX is considerably lower than that between mouse and rat autosomal genes, agreeing with previous observations and providing some evidence for stronger selective constraints on synonymous changes in X-linked genes than in autosomal genes. At the protein level ZFX has been highly conserved in all placental mammals studied while ZFY has been well conserved in primates and foxes but has evolved rapidly in mice and rats, possibly due to relaxation of functional constraints as a result of the development of X-inactivation of ZFX in rodents. The long persistence of the ZFY-ZFX gene pair in mammals provides some insight into the process of degeneration of Y-linked genes.Correspondence to: W.-H. Li     

Evolution of secondary structure in the family of 7SL-like RNAs

Primate and rodent genomes are populated with hundreds of thousands copies of Alu and B1 elements dispersed by retroposition, i.e., by genomic reintegration of their reverse transcribed RNAs. These, as well as primate BC200 and rodent 4.5S RNAs, are ancestrally related to the terminal portions of 7SL RNA sequence. The secondary structure of 7SL RNA (an integral component of the signal recognition particle) is conserved from prokaryotes to distant eukaryotic species. Yet only in primates and rodents did this molecule give rise to retroposing Alu and B1 RNAs and to apparently functional BC200 and 4.5S RNAs. To understand this transition and the underlying molecular events, we examined, by comparative analysis, the evolution of RNA structure in this family of molecules derived from 7SL RNA.RNA sequences of different simian (mostly human) and prosimian Alu subfamilies as well as rodent B1 repeats were derived from their genomic consensus sequences taken from the literature and our unpublished results (prosimian and New World Monkey). RNA secondary structures were determined by enzymatic studies (new data on 4.5S RNA are presented) and/or energy minimization analyses followed by phylogenetic comparison. Although, with the exception of 4.5S RNA, all 7SL-derived RNA species maintain the cruciform structure of their progenitor, the details of 7SL RNA folding domains are modified to a different extent in various RNA groups. Novel motifs found in retropositionally active RNAs are conserved among Alu and B1 subfamilies in different genomes. In RNAs that do not proliferate by retroposition these motifs are modified further. This indicates structural adaptation of 7SL-like RNA molecules to novel functions, presumably mediated by specific interactions with proteins; these functions were either useful for the host or served the selfish propagation of RNA templates within the host genome.Abbreviations FAM fossil Alu element - FLAM free left Alu monomer - FRAM free right Alu monomer - L-Alu left Alu subunit - R-Alu right Alu subunit Correspondence to: D. LabudaDedicated to Dr. Robert Cedergren on the occasion of his 25th anniversary at the University of Montreal     

The complete nucleotide sequence and gene organization of carp (Cyprinus carpio) mitochondrial genome

The complete sequence of the carp mitochondrial genome of 16,575 base pairs has been determined. The carp mitochondrial genome encodes the same set of genes (13 proteins, 2 rRNAs, and 22 tRNAs) as do other vertebrate mitochondrial DNAs. Comparison of this teleostean mitochondrial genome with those of other vertebrates reveals a similar gene order and compact genomic organization. The codon usage of proteins of carp mitochondrial genome is similar to that of other vertebrates. The phylogenetic relationship for mitochondrial protein genes is more apparent than that for the mitochondrial tRNA and rRNA genes.Correspondence to: F. Huang     

Inhibition of Glutamate Dehydrogenase in Brain Mitochondria and Synaptosomes by Mg2+ and Polyamines: A Possible Cause for Its Low In Vivo Activity

Abstract: Magnesium and the polyamines putrescine, spermidine, and spermine inhibited the activity of glutamate dehydrogenase in permeabilized rat brain mitochondria in a concentration-dependent manner. The inhibitory effect was observed on both the reductive amination of 2-oxoglutarate and oxidative deamination of glutamate, as well as in the presence and absence of ADP and leucine, the allosteric activators of the enzyme. Kinetic studies at various concentrations of substrates showed that inhibition by magnesium and spermine was very pronounced at 2-oxoglutarate concentrations less than 0.5 m M and NADH levels less than 0.08 m M . The presence of the former compounds also accentuated the inhibitory effect of high concentrations of 2-oxoglutarate (>2.0 m M ) and NADH (>0.32 m M ). Addition of magnesium and spermine to suspensions of synaptosomes decreased the amount of ammonia produced from glutamate. It is suggested that polyamines and magnesium, normal constituents of mammalian brain, are responsible, at least in part, for the low glutamate dehydrogenase activity in vivo.     

Cell Size and the Heat-Shock Response in Rat Brain

Abstract: The expression of mRNAs encoding two members of the heat-shock protein 70 family, the constitutively-expressed heat-shock cognate (hsc70) mRNA and the strictly heat-inducible (hsp70) mRNA, was quantitated in cerebellar and hippocampal cells of rats 3 h after amphetamine-induced or heat-induced hyperthermia. Intracellular heat-shock mRNA levels in specific cell types were compared with those of total polyadenylic acid [poly(A)] mRNA or 18S rRNA in the same cell type. Levels of poly(A) mRNAs, 18S rRNAs, and hsc70 mRNAs were highest in large neurons and lowest in glia. hsp70 mRNAs were also present at highest levels in large neurons, suggesting that hsp70 mRNAs accumulated as rapidly in these cell types as they did in small neurons and glia. However, compared with levels of intracellular poly(A) mRNAs or levels of rRNAs, large neurons contained two- to 12-fold lower levels of hsp70 mRNAs than neurons of intermediate size and five- to 30-fold lower levels than glia. These results suggest that hsp70 mRNAs accumulated as rapidly in large neurons as in small neurons and glia, but that the large size of these neurons precluded intracellular hsp70 mRNA concentrations increasing as quickly. The susceptibility of large neurons to stress-induced cell death could be due, in part, to their inability to synthesize rapidly hsp70 in sufficient amounts to protect these cells from the initial molecular consequences of stress.     

Effect of the Platelet-Activating Factor Antagonist BN 50739 and Its Diluents on Mitochondrial Respiration and Membrane Lipids During and Following Cerebral Ischemia

Abstract: Recent evidence suggests that platelet-activating factor plays a role in ischemia-induced neural injury. The Pulsinelli-Brierley four-vessel occlusion model was used to study the effect of a synthetic platelet-activating factor antagonist, BN 50739, and its solvents, either dimethyl sulfoxide or hydroxypropyl-β-cyclodextrin, on cerebral ischemia-reperfusion. Rats were subjected to either 30 min of ischemia or 30 min of ischemia followed by 60 min of recirculation. Changes in the brain mitochondrial free fatty acid pool size, fatty acyl composition of phospholipids, and respiratory function were monitored. When the BN 50739 (2 mg of BN 50739/kg of body weight i.v.) was administered at the onset of recirculation, it significantly reversed the ischemia-induced accumulation of mitochondrial free fatty acids and loss of polyunsaturated fatty acyl chains from phosphatidylcholine and phosphatidylethanolamine while simultaneously improving mitochondrial respiration. Dimethyl sulfoxide alone decreased the mitochondrial level of malonyldialdehyde and total free fatty acid pool size, but there was no improvement in mitochondrial respiration. Hydroxypropyl-β-cyclodextrin was reported to be pharmacologically inactive and capable of dissolving BN 50739. However, hydroxypropyl-β-cyclodextrin alone also caused a significant increase in content of cerebral mitochondrial membrane free fatty acids and hydrolysis of phosphatidylcholine in normoxic control animals. The overall effect of BN 50739 on mitochondrial structure and energy metabolism supports the hypothesis that platelet-activating factor may play a key role in ischemia-induced cerebral injury.