Two extremely eurythermal goby fishes, Gillichthys mirabilis and Giffichthys seta, which encounter habitat temperature variations of "30"C, showed seasonal matization of endogenous levels and of onset temperatures for enhanced synthesis of a 90-kDa-class heat shock protein (HSP90). Summer-acclimatized fishes had higher levels of HSP90 in brain tissue than winter-acclimatized specimens, as shown by Western blot analysis. For winter-acclimatized fishes, increased synthesis of HSP90 was observed when the temperature was raised from a control temperature (18C) to 28WC. For summer-acclimatized fish, no significantly increased synthesis of HSP90 occurred until the experimental temperature was raised to 32C. These data suggest that the threshold temperature at which enhanced expression of HSP-encoding genes occurs is not hard-wired genetically but may be subject to acclimatization. A causal relationship between seasonal changes in steady-state levels of HSP90 and the threshold temperature for enhanced HSP90 synthesis is discussed in terms of existing models for the regulation of HSP gene expression.Temperature regulation of gene expression is certain to be critical for the survival and success of ectothermic ("coldblooded") animals living in variable thermal environments. Presently, however, little is known about the interactions between temperature and gene regulation in eukaryotic organisms. The only well-understood example of temperature control of gene expression is that of the heat shock proteins (HSPs), a group of proteins whose synthesis can be induced by increases in temperature and by exposure to a variety of other stresses (e.g., heavy metals and alcohols). In addition to being stress-inducible, HSPs (or their cognates) exist as normal cellular constituents. The HSPs and their cognates have been implicated in various roles, from assisting in protein folding and oligomerization to steroid receptor activation and inactivation (1, 2). Both the HSPs and the heat shock response are highly conserved among phylogenetically divergent organisms (3), which attests to the critical' roles these molecules play in cellular function and adaptation.HSPs may play a role in physiological adaptation to environmental temperature change (e.g., during seasonal or diurnal shifts in ambient temperature). A clear relationship exists between different species' normal body temperatures and the temperatures at which HSP synthesis is induced; in the species so studied, HSP induction occurs at temperatures 5-10°C above normal body temperature (3), with some exceptions (4). Thermal induction may involve either the expression of a type of HSP not previously expressed or the enhanced expression of a class of HSP already present in the cell at some constitutive level. The correlation between normal body (cell) temperature and HSP induction temperature suggests that the HSP gene regulatory processes of different species have different set points (temperature thresholds) for heat-triggered induction of enhanced HSP production. However, ...

Dreissena polymorpha consumed about 6 x 108 Escherichia coli from 20 ml of artificial pondwater (APW) in 30 min under laboratory conditions. The clearance rate per mussel was 143 +/- 25 ml g-1 dry tissue min-1. The E. coli used in these studies ranged from about 1.7 to 2.9 {mu}m in length. 35S-labeled E. coli were used to demonstrate that bacteria-derived nutrients were incorporated into mussel tissue. Electrophoretic analysis of mussel and bacterial proteins on 12% polyacrylamide gels allowed the visual determination of incorporation of labeled amino acids into bivalve proteins and demonstrated that intact bacteria were not simply trapped in mussel tissues. The conversion of bacterial-labeled amino acids into mussel protein was about 26%. Similarly, we demonstrated that D. polymorpha can use other bacterial species ranging in size from about 1.3 to 4.1 μm, including Citrobacter freundii, Enterobacter aerogenes, Serratia marcescens, Bacillus megaterium, and B. subtilus. The ability of D. polymorpha to take up E. coli was compared with that of two other freshwater mussels, Corbicula fluminea and Carunculina texasensis. On a mussel-dry-weight basis, D. polymorpha cleared bacteria 30 to 100 times faster than Corbicula fluminea and Carunculina texasensis, respectively. The ability to filter E. coli appears to be related to the architecture of the cirri on the latero-frontal cells of the gill. Cirri from Corbicula and Dreissena are similar in size, but Dreissena has a larger gill compared to the tissue dry-weight, and has 102 times more cirri than found in Corbicula. Carunculina, the unionid representative, has smaller and fewer cirri, and has relatively limited ability to capture E. coli.

Nine species of unionids cleared laboratory-raised Escherichia coli from artificial pond water. The six unionid species collected from rivers had higher clearance rates than the three species collected from ponds, when clearance was normalized to millilitres per gram of dry tissue mass per minute. Analysis of variance indicated that all lotic unionids examined form a group with similar clearance rates. When normalized on the basis of gill surface area, rates of clearance by all of the lotic unionids become remarkably similar to one another regardless of mass, but differ significantly from those of the lentic unionids. The cirri found on the laterofrontal cells of the gills of lotic unionids tend to be complex, containing >25 cilia per cirral plate, while the cirri of the unionid species collected from ponds have smaller cirri ( < 16 cilia per cirral plate). There was a strong correlation between cirral surface area (mm2) per milligram of dry tissue and clearance rate among the unionid species studied. As a comparison, Corbicula jluminea and Dreissena polymorpha were also examined and both tended to clear bacteria more rapidly than the lotic unionids.RCsumC : Neuf espkces d'unionidae ont absorb6 tous les Escherichia coli eleves en laboratoire dans I'eau d'un etang artificiel. Les six espkces recoltees dans des rivikres avaient des taux de clearance plus rapides que les trois espkces provenant des ktangs aprks normalisation de la clearance pour l'exprimer en millilitres par gramme de tissu sec par minute. Les resultats d'une analyse de variance indiquent que tous les unionidits lotiques examines forment un groupe dont les taux de clearance sont semblables. En normalisant les donnees en fonction de la surface des branchies, les taux de clearance de tous les unionides lotiques deviennent remarquablement semblables les uns aux autres, quelle que soit la masse, mais diffkrent significativement de ceux des unionides Ienitiques. Les cirres observes sur les cellules latero-frontales des branchies chez les unionides lotiques tendent a etre complexes, contenant >25 cils par plaque, alors que les espkces provenant des etangs ont des cirres plus petits ( > 16 cils par plaque). I1 y a une forte correlation entre la surface du cirre (mm2) par milligramme de tissu sec et le taux de clearance chez les espkces etudiees. Pour fins de comparaison, Corbicula jluminea et Dreissena polymorpha ont egalement ete etudies et les deux espkces ont des taux de clearance de batteries plus rapides que les unionides lotiques. [Traduit par la Redaction]

Microscopic techniques were used to examine the role of gill cirri in particle capture by Dreissena polymorpha. The latero-frontal cirri, formed from two fused ciliary plates, consist of about 40 pairs of cilia. Each cilium in the plate contains a typical 9 + 2 axoneme in the fused region of the cirrus, but the structure of the axoneme in the long, free ciliary tips is reduced. The cilia in a cirrus are graded in length, with the shortest cilia positioned frontally. The cirral cilia move in unison, allowing the cirrus to move from a flexed position with its tip arched over the front of the gill filament, to an extended position with the cirrus projected in the plane of the latero-frontal cell and extending across the interfilament space. In the latter position, the free ciliary tips of opposing and neighboring cirri form a "trap" (net) with a spacing of about 0.5 μm. Observations with laser confocal microscopy indicated that these structures can physically trap particles <1 μm in diameter. Particles captured by the extended cirri are moved to the frontal surface of the gill, where the cirri are swept by the lateralmost frontal cilia. During cirral movement the shift from extended to flexed position is, in part, achieved by the base of the cirrus pivoting at a hinge region. Morphologically, the hinge region shows axonemal specializations that consist of electron-dense plates and other structures of undefined function that may be important in the overall movement of the cirrus. In addition to trapping by cirri, we also observed particles moving in the water currents, particularly in the frontal current located over the apical surface of the filament, suggesting that some particles are captured in these water currents without being physically trapped. Probably, therefore, trapping by the cirri and establishment of water currents by the filaments both participate in the interception of particles by Dreissena polymorpha.