Divergent Hemogen genes of teleosts and mammals share conserved roles in erythropoiesis: analysis using transgenic and mutant zebrafish

Hemogen is a vertebrate transcription factor that performs important functions in erythropoiesis and testicular development and may contribute to neoplasia. Here we identify zebrafish Hemogen and show that it is considerably smaller (∼22 kDa) than its human ortholog (∼55 kDa), a striking difference that is explained by an underlying modular structure. We demonstrate that Hemogens are largely composed of 21-25 amino acid repeats, some of which may function as transactivation domains (TADs). Hemogen expression in embryonic and adult zebrafish is detected in hematopoietic, renal, neural and gonadal tissues. Using Tol2- and CRISPR/Cas9-generated transgenic zebrafish, we show that Hemogen expression is controlled by two Gata1-dependent regulatory sequences that act alone and together to control spatial and temporal expression during development. Partial depletion of Hemogen in embryos by morpholino knockdown reduces the number of erythrocytes in circulation. CRISPR/Cas9-generated zebrafish lines containing either a frameshift mutation or an in-frame deletion in a putative, C-terminal TAD display anemia and embryonic tail defects. This work expands our understanding of Hemogen and provides mutant zebrafish lines for future study of the mechanism of this important transcription factor.

Summary: Transgenic and mutant zebrafish lines were created to characterize the expression and functions of Hemogen, a transcription factor involved in the formation of red blood cells and other processes.

Assisted protein folding at low temperature: evolutionary adaptation of the Antarctic fish chaperonin CCT and its client proteins

Eukaryotic ectotherms of the Southern Ocean face energetic challenges to protein folding assisted by the cytosolic chaperonin CCT. We hypothesize that CCT and its client proteins (CPs) have co-evolved molecular adaptations that facilitate CCT–CP interaction and the ATP-driven folding cycle at low temperature. To test this hypothesis, we compared the functional and structural properties of CCT–CP systems from testis tissues of an Antarctic fish, Gobionotothen gibberifrons (Lönnberg) (habitat/body T = −1.9 to +2°C), and of the cow (body T = 37°C). We examined the temperature dependence of the binding of denatured CPs (β-actin, β-tubulin) by fish and bovine CCTs, both in homologous and heterologous combinations and at temperatures between −4°C and 20°C, in a buffer conducive to binding of the denatured CP to the open conformation of CCT. In homologous combination, the percentage of G. gibberifrons CCT bound to CP declined linearly with increasing temperature, whereas the converse was true for bovine CCT. Binding of CCT to heterologous CPs was low, irrespective of temperature. When reactions were supplemented with ATP, G. gibberifrons CCT catalyzed the folding and release of actin at 2°C. The ATPase activity of apo-CCT from G. gibberifrons at 4°C was ∼2.5-fold greater than that of apo-bovine CCT, whereas equivalent activities were observed at 20°C. Based on these results, we conclude that the catalytic folding cycle of CCT from Antarctic fishes is partially compensated at their habitat temperature, probably by means of enhanced CP-binding affinity and increased flexibility of the CCT subunits.

Evolution and function of the globin intergenic regulatory regions of the antarctic dragonfishes (Notothenioidei: Bathydraconidae)

As the Southern Ocean cooled to -1.8 °C over the past 40 My, the teleostean clade Notothenioidei diversified and, under reduced selection pressure for an oxygen-transporting apparatus, became less reliant on hemoglobin and red blood cells. At the extreme of this trend, the crown group of Antarctic icefishes (Channichthyidae) lost both components of oxygen transport. Under the decreased selection scenario, we hypothesized that the Antarctic dragonfishes (Bathydraconidae, the red-blooded sister clade to the icefishes) evolved lower blood hemoglobin concentrations because their globin gene complexes (α- and β-globin gene pairs linked by a regulatory intergene) transcribe globin mRNAs less effectively than those of basal notothenioids (e.g., the Nototheniidae [notothens]). To test our hypothesis, we 1) sequenced the α/β-intergenes of the adult globin complexes of three notothen and eight dragonfish species and 2) measured globin transcript levels in representative species from each group. The typical nototheniid intergene was ∼3-4 kb in length. The bathydraconid intergenes resolved into three subclasses (long [3.8 kb], intermediate [3.0 kb], and short [1.5-2.3 kb]) that corresponded to the three subclades proposed for the taxon. Although they varied in length due to indels, the three notothen and eight dragonfish intergenes contained a conserved ∼90-nt element that we have previously shown to be required for globin gene transcription. Using the quantitative polymerase chain reaction, we found that globin mRNA levels in red cells from one notothen species and from one species of each dragonfish subclade were equivalent statistically. Thus, our results indicate that the bathydraconids have evolved adult globin loci whose regulatory intergenes tend to be shorter than those of the more basal nototheniids yet are equivalent in transcriptional efficacy. Their low blood hemoglobin concentrations are most likely due to reduction in hematocrit.

A model for cleavage plane determination in early amphibian and fish embryos

Current models for cleavage plane determination propose that metaphase spindles are positioned and oriented by interactions of their astral microtubules with the cellular cortex, followed by cleavage in the plane of the metaphase plate [1, 2]. We show that in early frog and fish embryos, where cells are unusually large, astral microtubules in metaphase are too short to position and orient the spindle. Rather, the preceding interphase aster centers and orients a pair of centrosomes prior to nuclear envelope breakdown, and the spindle assembles between these prepositioned centrosomes. Interphase asters center and orient centrosomes with dynein-mediated pulling forces. These forces act before astral microtubules contact the cortex; thus, dynein must pull from sites in the cytoplasm, not the cell cortex as is usually proposed for smaller cells. Aster shape is determined by interactions of the expanding periphery with the cell cortex or with an interaction zone that forms between sister-asters in telophase. We propose a model to explain cleavage plane geometry in which the length of astral microtubules is limited by interaction with these boundaries, causing length asymmetries. Dynein anchored in the cytoplasm then generates length-dependent pulling forces, which move and orient centrosomes.

A genomic fossil reveals key steps in hemoglobin loss by the antarctic icefishes

Antarctic icefishes are the only vertebrates that do not have hemoglobin and erythrocytes in their blood. These startling phenotypes are associated in several icefish species with deletions of juvenile and adult globin loci, which in red-blooded teleosts are typically composed of tightly linked pairs of alpha- and beta-globin genes. It is unknown if the loss of hemoglobin expression in icefishes was the direct result of such deletions or if other mutational events compromised globin chain synthesis prior to globin gene loss. In this study, we show that 15 of the 16 icefish species have lost the adult beta-globin gene but retain a truncated alpha-globin pseudogene. Surprisingly, a phylogenetically derived icefish species, Neopagetopsis ionah, possesses a complete, but nonfunctional, adult alphabeta-globin complex. This cluster contains 2 distinct beta-globin pseudogenes whose phylogenetic origins span the entire Antarctic notothenioid radiation, consistent with an origin via introgression. Maximum likelihood ancestral state reconstruction supports a scenario of icefish globin gene evolution that involves a single loss of the transcriptionally active adult alphabeta-globin cluster prior to the diversification of the extant species in the clade. Through lineage sorting of ancestral polymorphism, 2 types of alleles became fixed in the clade: 1) the alpha-globin pseudogene of the majority of species and 2) the inactive alphabeta-globin complex of N. ionah. We conclude that the globin pseudogene complex of N. ionah is a "genomic fossil" that reveals key intermediate steps on the pathway to loss of hemoglobin expression by all icefish species.

Characterization of the cytoplasmic chaperonin containing TCP-1 from the Antarctic fish Notothenia coriiceps

The cytoplasmic chaperonin containing TCP-1 (CCT) plays a critically important role in the folding and biogenesis of many cytoskeletal proteins, including tubulin and actin. For marine ectotherms, the chronically cold Southern Ocean (-2 to +2 degrees C) poses energetic challenges to protein folding, both at the level of substrate proteins and with respect to the chaperonin/chaperone folding system. Here we report the partial functional and structural characterization of CCT from an Antarctic notothenioid fish, Notothenia coriiceps. We find that the mechanism of folding by the Antarctic fish CCT differed from that of mammalian CCT: (1) the former complex was able to bind denatured beta-tubulin but (2) when reconstituted with rabbit Cofactor A, failed to release the protein to yield the tubulin/cofactor intermediate. Moreover, the amino acid sequences of the N. coriiceps CCT beta and theta chains contained residue substitutions in the equatorial, apical, and intermediate domains that would be expected to increase the flexibility of the subunits, thus facilitating function of the chaperonin in an energy poor environment. Our work contributes to the growing realization that protein function in cold-adapted organisms reflects a delicate balance between the necessity of structural flexibility for catalytic activity and the concomitant hazard of cold-induced denaturation.

bloodthirsty, an RBCC/TRIM gene required for erythropoiesis in zebrafish

The Antarctic icefishes (family Channichthyidae, suborder Notothenioidei) constitute the only vertebrate taxon that fails to produce red blood cells. These fishes can be paired with closely related, but erythrocyte-producing, notothenioids to discover erythropoietic genes via representational difference analysis. Using a B30.2-domain-encoding DNA probe so derived from the hematopoietic kidney (pronephros) of a red-blooded Antarctic rockcod, Notothenia coriiceps, we discovered a related, novel gene, bloodthirsty (bty), that encoded a 547-residue protein that contains sequential RING finger, B Box, coiled-coil, and B30.2 domains. bty mRNA was expressed by the pronephric kidney of N. coriiceps at a steady-state level 10-fold greater than that found in the kidney of the icefish Chaenocephalus aceratus. To test the function of bty, we cloned the orthologous zebrafish gene from a kidney cDNA library. Whole-mount in situ hybridization of zebrafish embryos showed that bty mRNA was present throughout development and, after the mid-blastula transition, was expressed in the head and in or near the site of primitive erythropoiesis in the tail just prior to red cell production. One- to four-cell embryos injected with two distinct antisense morpholino oligonucleotides (MOs) targeted to the 5'-end of the bty mRNA failed to develop red cells, whereas embryos injected with 4- and 5-bp mismatch control MOs produced wild-type quantities of erythrocytes. The morphant phenotype was rescued by co-injection of synthetic bty mRNA containing an artificial 5'-untranslated region (UTR) with the antisense MO that bound the 5'-UTR of the wild-type bty transcript. Furthermore, the expression of genes that mark terminal erythroid differentiation was greatly reduced in the antisense-MO-treated embryos. We conclude that bty is likely to play a role in differentiation of the committed red cell progenitor.

Posttranslational Modification of Brain Tubulins from the Antarctic Fish Notothenia coriiceps: Reduced C-Terminal Glutamylation Correlates with Efficient Microtubule Assembly at Low Temperature

We have shown previously that the tubulins of Antarctic fish assemble into microtubules efficiently at low temperatures (-2 to +2 degrees C) due to adaptations intrinsic to the tubulin subunits. To determine whether changes in posttranslational glutamylation of the fish tubulins may contribute to cold adaptation of microtubule assembly, we have characterized C-terminal peptides from alpha- and beta-tubulin chains from brains of adult specimens of the Antarctic rockcod Notothenia coriiceps by MALDI-TOF mass spectrometry and by Edman degradation amino acid sequencing. Of the four fish beta-tubulin isotypes, nonglutamylated isoforms were more abundant than glutamylated isoforms. In addition, maximal glutamyl side-chain length was shorter than that observed for mammalian brain beta tubulins. For the nine fish alpha-tubulin isotypes, nonglutamylated isoforms were also generally more abundant than glutamylated isoforms. When glutamylated, however, the maximal side-chain lengths of the fish alpha tubulins were generally longer than those of adult rat brain alpha chains. Thus, Antarctic fish adult brain tubulins are glutamylated differently than mammalian brain tubulins, resulting in a more heterogeneous population of alpha isoforms and a reduction in the number of beta isoforms. By contrast, neonatal rat brain tubulin possesses low levels of glutamylation that are similar to that of the adult fish brain tubulins. We suggest that unique residue substitutions in the primary structures of Antarctic fish tubulin isotypes and quantitative changes in isoform glutamylation act synergistically to adapt microtubule assembly to low temperatures.

Designing a safer workplace: importance of job autonomy, communication quality, and supportive supervisors

The direct and indirect effects of work characteristics on self-reported safe working were investigated in a longitudinal study of frontline manufacturing employees (N = 161). The work characteristics included job autonomy, role overload, role conflict, supportive supervision, training adequacy, job security, and communication quality. Job autonomy and communication quality were positively associated with safe working after prior levels of these variables were controlled for, and supportive supervision had a lagged positive effect on safe working 18 months later. Additional analyses showed that organizational commitment fully mediated the effect of job autonomy on safe working and partially mediated the effect of communication quality on safe working. The study suggests that work characteristics are important antecedents of safe working.

Cold adaptation of microtubule assembly and dynamics. Structural interpretation of primary sequence changes present in the alpha- and beta-tubulins of Antarctic fishes

The microtubules of Antarctic fishes, unlike those of homeotherms, assemble at very low temperatures (-1.8 degrees C). The adaptations that enhance assembly of these microtubules are intrinsic to the tubulin dimer and reduce its critical concentration for polymerization at 0 degrees C to approximately 0.9 mg/ml (Williams, R. C., Jr., Correia, J. J., and DeVries, A. L. (1985) Biochemistry 24, 2790-2798). Here we demonstrate that microtubules formed by pure brain tubulins of Antarctic fishes exhibit slow dynamics at both low (5 degrees C) and high (25 degrees C) temperatures; the rates of polymer growth and shortening and the frequencies of interconversion between these states are small relative to those observed for mammalian microtubules (37 degrees C). To investigate the contribution of tubulin primary sequence variation to the functional properties of the microtubules of Antarctic fishes, we have sequenced brain cDNAs that encode 9 alpha-tubulins and 4 beta-tubulins from the yellowbelly rockcod Notothenia coriiceps and 4 alpha-tubulins and 2 beta-tubulins from the ocellated icefish Chionodraco rastrospinosus. The tubulins of these fishes were found to contain small sets of unique or rare residue substitutions that mapped to the lateral, interprotofilament surfaces or to the interiors of the alpha- and beta-polypeptides; longitudinal interaction surfaces are not altered in the fish tubulins. Four changes (A278T and S287T in alpha; S280G and A285S in beta) were present in the S7-H9 interprotofilament "M" loops of some monomers and would be expected to increase the flexibility of these regions. A fifth lateral substitution specific to the alpha-chain (M302L or M302F) may increase the hydrophobicity of the interprotofilament interaction. Two hydrophobic substitutions (alpha:S187A in helix H5 and beta:Y202F in sheet S6) may act to stabilize the monomers in conformations favorable to polymerization. We propose that cold adaptation of microtubule assembly in Antarctic fishes has occurred in part by evolutionary restructuring of the lateral surfaces and the cores of the tubulin monomers.

Minimizing strain and maximizing learning: the role of job demands, job control, and proactive personality

Using a sample of 268 production employees, this study extended research on R. Karasek's (1979) demands-control model of stress in 2 ways. First, results show that R. Karasek's proposed interaction between demands and control when predicting strain occurred only for more proactive employees. This 3-way interaction helps reconcile previous inconsistent findings about the interaction between demands and control when predicting strain. Second, the study extends research by investigating the demands-control interaction and the moderating influence of proactive personality in relation to learning-oriented outcomes (perceived mastery, role breadth self-efficacy, and production ownership). There were no 3-way interactions among the variables when predicting these learning-oriented outcomes, but all were important predictors. These results show (a) that demands and control can influence learning as proposed in the dynamic version of the demands-control model and (b) that proactive personality plays an important moderating role.

Rushed, unhappy, and drained: an experience sampling study of relations between time pressure, perceived control, mood, and emotional exhaustion in a group of accountants

Experience sampling methodology was used to examine how work demands translate into acute changes in affective response and thence into chronic response. Seven accountants reported their reactions 3 times a day for 4 weeks on pocket computers. Aggregated analysis showed that mood and emotional exhaustion fluctuated in parallel with time pressure over time. Disaggregated time-series analysis confirmed the direct impact of high-demand periods on the perception of control, time pressure, and mood and the indirect impact on emotional exhaustion. A curvilinear relationship between time pressure and emotional exhaustion was shown. The relationships between work demands and emotional exhaustion changed between high-demand periods and normal working periods. The results suggest that enhancing perceived control may alleviate the negative effects of time pressure.

Rushed, unhappy, and drained: an experience sampling study of relations between time pressure, perceived control, mood, and emotional exhaustion in a group of accountants

Experience sampling methodology was used to examine how work demands translate into acute changes in affective response and thence into chronic response. Seven accountants reported their reactions 3 times a day for 4 weeks on pocket computers. Aggregated analysis showed that mood and emotional exhaustion fluctuated in parallel with time pressure over time. Disaggregated time-series analysis confirmed the direct impact of high-demand periods on the perception of control, time pressure, and mood and the indirect impact on emotional exhaustion. A curvilinear relationship between time pressure and emotional exhaustion was shown. The relationships between work demands and emotional exhaustion changed between high-demand periods and normal working periods. The results suggest that enhancing perceived control may alleviate the negative effects of time pressure.

Evolution, organization, and expression of alpha-tubulin genes in the antarctic fish Notothenia coriiceps. Adaptive expansion of a gene family by recent gene duplication, inversion, and divergence

To assess the organization and expression of tubulin genes in ectothermic vertebrates, we have chosen the Antarctic yellowbelly rockcod, Notothenia coriiceps, as a model system. The genome of N. coriiceps contains approximately 15 distinct DNA fragments complementary to alpha-tubulin cDNA probes, which suggests that the alpha-tubulins of this cold-adapted fish are encoded by a substantial multigene family. From an N. coriiceps testicular DNA library, we isolated a 13.8-kilobase pair genomic clone that contains a tightly linked cluster of three alpha-tubulin genes, designated NcGTbalphaa, NcGTbalphab, and NcGTbalphac. Two of these genes, NcGTbalphaa and NcGTbalphab, are linked in head-to-head (5' to 5') orientation with approximately 500 bp separating their start codons, whereas NcGTbalphaa and NcGTbalphac are linked tail-to-tail (3' to 3') with approximately 2.5 kilobase pairs between their stop codons. The exons, introns, and untranslated regions of the three alpha-tubulin genes are strikingly similar in sequence, and the intergenic region between the alphaa and alphab genes is significantly palindromic. Thus, this cluster probably evolved by duplication, inversion, and divergence of a common ancestral alpha-tubulin gene. Expression of the NcGTbalphac gene is cosmopolitan, with its mRNA most abundant in hematopoietic, neural, and testicular tissues, whereas NcGTbalphaa and NcGTbalphab transcripts accumulate primarily in brain. The differential expression of the three genes is consistent with distinct suites of putative promoter and enhancer elements. We propose that cold adaptation of the microtubule system of Antarctic fishes is based in part on expansion of the alpha- and beta-tubulin gene families to ensure efficient synthesis of tubulin polypeptides.

Enhancing role breadth self-efficacy: the roles of job enrichment and other organizational interventions

Role breadth self-efficacy (RBSE) refers to employees' perceived capability of carrying out a broader and more proactive set of work tasks that extend beyond prescribed technical requirements. A newly developed scale of RBSE was internally consistent and distinct from the related concepts of proactive personality and self-esteem. In an initial cross-sectional study (N = 580), work design variables (job enrichment, job enlargement, and membership of improvement groups) were the key organizational predictors of RBSE. These investigations were repeated in a second cross-sectional study (N = 622) and extended by examining change over time (N = 459). The longitudinal analysis showed that increased job enrichment and increased quality of communication predicted the development of greater self-efficacy.

The major adult alpha-globin gene of antarctic teleosts and its remnants in the hemoglobinless icefishes. Calibration of the mutational clock for nuclear genes

The icefishes of the Southern Ocean (family Channichthyidae, suborder Notothenioidei) are unique among vertebrates in their inability to synthesize hemoglobin. We have shown previously (Cocca, E., Ratnayake-Lecamwasam, M., Parker, S. K., Camardella, L., Ciaramella, M., di Prisco, G., and Detrich, H. W., III (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 1817-1821) that icefishes retain inactive genomic remnants of adult notothenioid alpha-globin genes but have lost the gene that encodes adult beta-globin. Here we demonstrate that loss of expression of the major adult alpha-globin, alpha1, in two species of icefish (Chaenocephalus aceratus and Chionodraco rastrospinosus) results from truncation of the 5' end of the notothenioid alpha1-globin gene. The wild-type, functional alpha1-globin gene of the Antarctic yellowbelly rockcod, Notothenia coriiceps, contains three exons and two A + T-rich introns, and its expression may be controlled by two or three distinct promoters. Retained in both icefish genomes are a portion of intron 2, exon 3, and the 3'-untranslated region of the notothenioid alpha1-globin gene. The residual, nonfunctional alpha-globin gene, no longer under positive selection pressure for expression, has apparently undergone random mutational drift at an estimated rate of 0.12-0.33%/million years. We propose that abrogation of hemoglobin synthesis in icefishes most likely resulted from a single mutational event in the ancestral channichthyid that deleted the entire beta-globin gene and the 5' end of the linked alpha1-globin gene.

Work characteristics and employee well-being within a context of strategic downsizing

Findings from this 4-year longitudinal study of strategic downsizing suggest that introducing deliberate work organization and change management strategies can combat the negative effects of reduced head count. Results showed that there was no overall decrease in well-being from before to after downsizing for the 139 employees remaining in an organization, despite an increase in work demands. The potential detrimental effect of demands appears to have been offset by improvement in work characteristics arising from initiatives introduced as part of the downsizing strategy. This interpretation is consistent with analyses at the individual level, which showed that high demands were associated with poorer well-being but that increases in control, clarity, and participation were associated with improved well-being.

Work characteristics and employee well-being within a context of strategic downsizing

Findings from this 4-year longitudinal study of strategic downsizing suggest that introducing deliberate work organization and change management strategies can combat the negative effects of reduced head count. Results showed that there was no overall decrease in well-being from before to after downsizing for the 139 employees remaining in an organization, despite an increase in work demands. The potential detrimental effect of demands appears to have been offset by improvement in work characteristics arising from initiatives introduced as part of the downsizing strategy. This interpretation is consistent with analyses at the individual level, which showed that high demands were associated with poorer well-being but that increases in control, clarity, and participation were associated with improved well-being.

Directional Spread of Septoria Leaf Spot in Tomato Rows

Disease severity of Septoria leaf spot in rows of fresh-market tomato plants that were not staked was assessed in 1992 and 1993 following inoculation of the center plant in each row. Both temporal disease increase and spatial disease gradients were best described by the logistic model. Apparent infection rates for Septoria leaf spot epidemics averaged 0.282 day^-1 (SE = 0.015, r² = 0.96, P < 0.0001) in 1992 and 0.260 day^-1 (SE = 0.011, r² = 0.96, P < 0.0001) in 1993. Apparent infection rates remained relatively constant at increasing distances from initial foci. Estimated values for disease gradient slopes 3 to 5 weeks after inoculation ranged from -0.26 to -1.05 m^-1. Velocities of disease spread ranged from 0.3 to 1.3 m/day. Results of analysis of disease severity data for these 2 years suggest that Septoria leaf spot epidemics can develop at rapid rates, but steep disease gradients limit the velocity of spread.

Inner and outer arm axonemal dyneins from the Antarctic rockcod Notothenia coriiceps

Adaptive compensation of enzymatic activities is common among cold-living poikilotherms. Their enzymes often demonstrate higher activities at low temperatures than do homologs from temperate or thermophilic species. To understand the molecular features necessary for cold adaptation of microtubule motor proteins, we have initiated studies of the flagellar dynein ATPases of Antarctic fishes (body temperature range = -1.8 to +2 degrees C). Dyneins were isolated by high-salt extraction of demembranated sperm axonemes from the Antarctic yellowbelly rockcod, Notothenia coriiceps. Although solubilization of inner arms was incomplete, an inner arm dynein was recognized as a discrete complex containing one major dynein heavy chain (DHC) and sedimenting through sucrose gradients at approximately 12 S. Like inner arm dyneins from Chlamydomonas, the fish complex contained an actin-immunoreactive protein of 43 kDa and a 30-kDa protein. One isoform of the inner arm DHC gene family of N. coriiceps was detected by the polymerase chain reaction, and Southern analysis established that this DHC gene is present at one copy per haploid genome. Outer arm dynein was extracted quantitatively by high-salt treatment, contained two DHCs (one major, one minor), and sedimented through sucrose gradients as a polydisperse, aggregating system. Associated with the outer arm DHCs were five presumptive intermediate chains (ICs) of 66-91 kDa, immunologically defined by their cross-reactivity to four monoclonal antibodies specific for ICs from other organisms. The basal (non-microtubule-stimulated) specific ATPase activities of the N. coriiceps inner and outer arm dyneins were approximately 0.07 and approximately 0.04 micromol of P(i) min(-1) mg(-1), respectively, at 0 degrees C, attained their maxima (approximately 0.1 micromol of P(i) min(-1) mg(-1)) at 9 and 19 degrees C, respectively, and at higher temperatures declined substantially. Furthermore, the activities of the fish dyneins at temperatures < or = 15 degrees C were significantly larger than that of outer arm dynein from the mesophile Tetrahymena. These results suggest that the greater catalytic efficiencies of N. coriiceps inner and outer arm dyneins at low temperatures are due to enhanced polypeptide flexibility in the active sites of their protein subunits. We conclude that temperature adaptation of flagellar dyneins from Antarctic fishes is compatible with substantial conservation of primary and quaternary structure.

Genomic remnants of alpha-globin genes in the hemoglobinless antarctic icefishes

Alone among piscine taxa, the antarctic icefishes (family Channichthyidae, suborder Notothenioidei) have evolved compensatory adaptations that maintain normal metabolic functions in the absence of erythrocytes and the respiratory oxygen transporter hemoglobin. Although the uniquely "colorless" or "white" condition of the blood of icefishes has been recognized since the early 20th century, the status of globin genes in the icefish genomes has, surprisingly, remained unexplored. Using alpha- and beta-globin cDNAs from the antarctic rockcod Notothenia coriiceps (family Nototheniidae, suborder Notothenioidei), we have probed the genomes of three white-blooded icefishes and four red-blooded notothenioid relatives (three antarctic, one temperate) for globin-related DNA sequences. We detect specific, high-stringency hybridization of the alpha-globin probe to genomic DNAs of both white- and red-blooded species, whereas the beta-globin cDNA hybridizes only to the genomes of the red-blooded fishes. Our results suggest that icefishes retain inactive genomic remnants of alpha-globin genes but have lost, either through deletion or through rapid mutation, the gene that encodes beta-globin. We propose that the hemoglobinless phenotype of extant icefishes is the result of deletion of the single adult beta-globin locus prior to the diversification of the clade.

Polymerization of Antarctic fish tubulins at low temperatures: role of carboxy-terminal domains

We have proposed previously that the efficient polymerization of tubulins from Antarctic fishes at low, physiological temperatures (-1.8 to +2 degrees C) may result in part from adaptations (e.g., reductions in acidic residues) located in their carboxy-terminal (C-terminal) tails [Detrich & Overton (1986) J. Biol. Chem. 261, 10922-10930]. To test this hypothesis, we have examined the polymerization of Antarctic fish neural tubulins modified at their C termini by proteolysis or by neutralization of carboxyl groups. Addition of subtilisin to low concentrations of Notothenia coriiceps tubulin induced a biphasic assembly reaction: stage I corresponded to the C-terminal cleavage of beta chains to produce alpha beta s dimers, and stage II coincided with the slower, C-terminal cleavage of alpha chains to yield alpha s beta s. Both stage I and stage II polymers consisted of protofilament sheets and microtubules with attached sheets. The critical concentration for assembly of the stage II polymer was at least 10-fold lower than that of untreated tubulin. Neutralization of Glu and Asp carboxyls in Gobionotothen gibberifrons microtubules by the carbodiimide-catalyzed incorporation of glycine ethyl ester (GEE) moieties produced a tubulin, modified largely in its C termini, that assembled more readily than did control tubulin. When 12 GEE groups were incorporated per dimer, the critical concentrations for assembly of modified tubulin at 5-10 degrees C were 2-3-fold smaller than those for the unmodified protein. Comparably modified bovine tubulin (10 GEE/dimer) assembled at 37 degrees C with a critical concentration 2.6-fold lower than that for the unmodified tubulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Divergent neural beta tubulin from the Antarctic fish Notothenia coriiceps neglecta: potential sequence contributions to cold adaptation of microtubule assembly

The cytoplasmic microtubules of the cold-adapted Antarctic fishes, unlike those of homeotherms and temperate poikilotherms, assemble and function at body temperatures in the range -1.8 to +2 degrees C. To determine whether alterations to the primary sequence of beta tubulin may contribute to enhancement of microtubule assembly at cold temperatures, we have cloned and sequenced a 1.8-kilobase neural beta-chain cDNA, Ncn beta 1, from an Antarctic rockcod, Notothenia coriiceps neglecta. Based on nucleotide sequence homology, Ncn beta 1 probably corresponds to a class-II beta-tubulin gene. The 446-residue beta chain encoded by Ncn beta 1 is closely related (sequence homology approximately 95%) both to the neural class-I/II isotypes and to the neural/testicular class-IV variants of higher vertebrates, but the sequence of its carboxy-terminal isotype-defining region (residues 431-446) has diverged markedly (> or = 25% change relative to the I/II/IV referents). Furthermore, the Ncn beta 1 polypeptide contains six unique amino-acid substitutions (five conservative, one nonconservative) not found in other vertebrate brain isotypes, and the carboxy-terminal region possesses a unique tyrosine inserted at position 442. We conclude that Ncn beta 1 encodes a class-II beta tubulin that contains sequence modifications, located largely in its interdimer contact domain, that may contribute to cold adaptation of microtubule assembly.