An X-autosome fusion chromosome of Caenorhabditis elegans

Summary The translocation mnT12(IV;X) is a fusion of holocentric chromosomes IV and X, the breakpoints occurring near the left end of IV and the right end of X. Animals homozygous for mnT12 are viable and fertile; they contain five pairs of chromosomes rather than the normal set of six pairs. The mnT12 chromosome is larger than all wild-type chromosomes and thus identifies linkage groups IV and X cytologically. Hermaphrodites heterozygous for mnT12 show high frequency meiotic nondisjunction both between mnT12 and the X chromosome, which results in a high incidence of male self progeny (27% compared to the wild-type incidence of 0.2%), and between mnT12 and chromosome IV, which results in a high incidence of self progeny essentially trisomic for chromosome IV (karyotype IV/mnT12/mnT12). The viability of chromosome IV trisomics has been confirmed by constructing animals trisomic for only normal copies of chromosome IV; these animals are morphologically wild type. Meiotic chromosome disjunction in mnT12 homozygotes appears to be normal, although the frequency of recombination between markers that are normally X-linked is significantly reduced. Males of genotype IV/mnT12/0 are fertile. They can be thought of as having a neo-X(mnT12) neo-Y(normal IV) karyotype since it is possible to maintain a male-hermaphrodite stock of C. elegans consisting of such males and hermaphrodites carrying two neo-X chromosomes and no neo-Y; the organism is thus converted from an XO:XX type of sex determination to an XX:XX system.     

Soil respiration of Alaskan tundra at elevated atmospheric carbon dioxide concentrations

Summary CO₂ efflux from tussock tundra in Alaska that had been exposed to elevated CO₂ for 2.5 growing seasons was measured to assess the effect of long- and short-term CO₂ enrichment on soil respiration. Long-term treatments were: 348, 514, and 683 μll⁻¹ CO₂ and 680 μll⁻¹ CO₂+4°C above ambient. Measurements were made at 5 CO₂ concentrations between 87 and 680 μll⁻¹ CO₂. Neither long- or short-term CO₂ enrichment significantly affected soil CO₂ efflux. Tundra developed at elevated temperature and 680 μll⁻¹ CO₂ had slightly higher, but not statistically different, mean respiration rates compared to untreated tundra and to tundra under CO₂ control alone.     

Extracellular Overflow of Neuroactive Amino Acids During Severe Insulin-Induced Hypoglycemia: In Vivo Dialysis of the Rat Hippocampus

Hypoglycemia-evoked changes in levels of extracellular excitatory and inhibitory amino acids were studied using the microdialysis technique. A newly designed dialysis probe was inserted stereotaxically into the rat hippocampus. Animals were then subjected to insulin-induced hypoglycemia; then blood glucose levels were restored by glucose injections after a 30-min period of isoelectric electroencephalography. Dialysates were collected before, during, and after the isoelectric period. Amino acids in the dialysates were analyzed by liquid chromatography and fluorescence detection following automatic precolumn derivatization with o-phthaldialdehyde. During the isoelectric phase, the concentration of aspartate increased 15-fold, whereas glutamate, gamma-amino-butyric acid, taurine, and phosphoethanolamine levels were elevated three- to sixfold. Smaller increases were observed for nonneuroactive amino acids such as asparagine, alanine, and phenylalanine. In contrast to all other amino acids, the glutamine content was reduced to less than 30% of preisoelectric values. The concentrations of the neuroactive amino acids were restored to normal in the post-isoelectric phase. These data demonstrate that there is an extracellular overflow of neuroactive amino acids, especially aspartate, during severe hypoglycemia.     

Correlation of Rates of Calcium Entry and Release of Endogenous Norepinephrine in Rat Brain Region Synaptosomes

Voltage-dependent 45Ca2+ uptake and endogenous norepinephrine (NE) release were measured simultaneously in synaptosomes isolated from rat hypothalamus, brainstem, and cerebellum at 1, 3, 5, 15, and 30 s. In synaptosomes depolarized by 125 mM KCl, 45Ca2+ uptake and NE release exhibited fast and slow components. Rates of NE release and 45Ca2+ uptake were fastest from 0 to 1 s. NE release and 45Ca2+ uptake rates from 1 to 5 s were less than 15% of 0-1 s rates. Both resting (5 mM KCl) and depolarization-induced (125 mM KCl) NE release paralleled 45Ca2+ uptake from 1 to 30 s. Voltage-dependent NE release was approximately 1% and 2% of total synaptosomal NE content at 1- and 30-s measurement intervals, respectively, and did not differ between the three brain regions studied. Calcium and potassium dependence studies showed that NE release was stimulated by increased potassium and that depolarization-induced NE release was dependent on the presence of external calcium. These results show that calcium-dependent NE release from synaptosomes is correlated with calcium entry. Both processes exhibit fast and slow temporal components.     

Cellular retinoic acid-binding protein and its relationship to the biological activity of four synthetic retinoids in hamster tracheal organ culture

Summary The mechanism of action of retinoid in reversing keratinization in hamster trachea is yet unknown. The purpose of this study was to determine if cellular retinoic acid binding protein (CRABP) is present in tracheal epithelium following incubation in serum-free, vitamin A-deficient culture medium for 10 days, and if the effectiveness of a retinoid in reversing keratinization in organ culture is correlated with its ability to compete for CRABP sites. The cytosol prepared from tracheal cultures contained CRABP at a concentration of 2.61 pmoles per mg protein. Of the four retinoids with carboxyl end group selected for the study, two of the biological active retinoids competed for the CRABP sites. However, no correlation was observed between the biological activity of the inactive retinoids and their ability to associate with the CRABP sites. These results indicate that even though the action of retinoid may be mediated by retinoid binding protein, it cannot be used as a sole predicator of retinoid response in hamster trachea. This investigation was supported by Contract N01-CP-31012 and U. S. P. H. Grants CA30512 and CA32428, which were awarded by the Division of Cancer Etiology, National Cancer Institute, DHHS. Editor's Statement Tracheal organ cultures provide a useful model for the study of epithelial differentiation and carcinogenesis. Much attention has been given to the action of retinoids in this process. Mehta et al. demonstrate a lack of correlation between biological activity and specific cytosolic binding of members of this class of compounds, pointing out the need for a more complete biochemical understanding of the mechanism of action and active forms of retinoids in this and other systems in vivo and in vitro. David W. Barnes     

Foraging-efficiency-predation-risk trade-off in the grey squirrel

Many animals must often respond to environmental patterns that simulatneously influence both foraging efficiency and predation risk. We noted that grey squirrels (Sciurus carolinensis) sometimes immediately consume food items in areas of relatively great exposure to predators, and at other times carry food items to the safety of a tree prior to consumption. We outlined a hypothesis that the squirrels were somehow trading-off energy intake rate against predation risk. A simple model shows that maximal energetic efficiency is associated with immediate consumption, whereas (under the field conditions studied) carrying items to the safety of trees provides for minimal exposure to predation. Our analysis of the model predicts that the tendency to carry a food item should decrease with distance of food from cover (travel time) and increase with item size (handling time). To test our predictions, we presented free-roaming grey squirrels with patches containing a fixed number of identical food items. We estimated the proportion of items carried to trees before consumption for 12 different combinations of distance to the nearest tree and item size. The results support our hypothesis and indicate that a simple behavioural criterion based solely on foraging rate or time exposed to predators is insufficient to explain the variation in the data.     

An information-theory analysis of task specialization among worker honey bees performing hive duties

Worker honey bees (Apis mellifera) performing field duties are known to possess individual task specializations. However, little evidence has been forthcoming about individual specializations among the younger pre-foraging worker bees performing hive duties. This paper reports results obtained from behavioural observations of worker bees in seven hives. An information-theory analysis of these data reveals that the divergence from independence (D₂) of worker bee identity and behavioural pattern performed has a low value in all of the experimental hives. Young worker bees performing hive duties therefore do not possess detectable individual specializations. Environmental and life-history considerations that may account for this difference in behaviour between field and hive worker bees are discussed.     

Spatial variation in larval concentrations as a cause of spatial variation in settlement for the barnacle,Balanus glandula

Summary Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.     

Monoclonal antibodies to epitopes on different regions of the 200 00 dalton neurofilament protein : Probes for the geometry of the filament

Neurofilaments in mammalian nervous tissues have three subunit proteins. These subunit proteins have apparent molecular masses of 200 (NF200), 150 (NF150) and 68 (NF68) kD. Biochemical assembly studies have indicated that the NF68 protein forms the core of the filament and that the other two proteins are associated proteins. Electron microscopy immunolocalization studies have been performed previously on isolated filaments and on filaments from neurons in culture, and have confirmed the localization of NF68 as a core filament protein and NF200 as a peripheral protein. We have raised two monoclonal antibodies to the NF200 components. Using immunogold labelled protein A, we have been able to localize these antibodies to tissue sections of adult cerebellum at the EM level. With this method, we have found that one of the monoclonal antibodies (NF2) shows a linear arrangement of gold particles directly on the filament, whereas the second monoclonal antibody (NF111) reacts with the filaments to give a periodic arrangement of gold particles. By immunoblotting against chymotryptic fragments of the NF200 protein, we have found that the mAB-NF111 reacts solely with a 160 kD piece, whereas the other monoclonal antibody reacts with both the 160 kD piece and the 40 kD piece. The latter piece was shown to be associated to the filament by binding studies with iodinated NF68. Thus the EM localization studies and the biochemical studies indicate that the two monoclonal antibodies react with different parts of the NF200 molecule, one binding to a part of the molecule which is located closer to the filament, and one to a more peripheral part of the molecule.     

Genetic Variation for the Sex Ratio in NASONIA VITRIPENNIS

We detected genetic variation for the sex ratio in the parasitoid wasp Nasonia vitripennis by analysis of inbred lines and with an artificial selection experiment. Sex ratios differed significantly among five independently isolated lines. Furthermore, sex ratio in broods produced by single females in single hosts shifted from 80-90% female to 50-55% female in 13 to 15 generations in each of two replicate selection lines. The final sex ratios of both selection lines were significantly lower than any of the inbred line sex ratios. Backcrosses revealed that the selection response was due to nuclear genes acting through the female parent. In light of known facultative sex ratio behavior and major genes affecting sex ratio in Nasonia, our results suggest that population and individual sex ratios in this species are molded by processes at both genetic and behavioral levels.