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Biomedical subjects

E Nevo

Publications and source records attributed to E Nevo.

At least 181 records · Page 10Linked to original sources
PubMed1985

Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi).

The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi; Rodentia) both have degenerated eyes as a convergent adaptation to subterranean life. The rudimentary eye lenses of these blind mammals no longer function in a visual process. The crystallin genes, which display a lens-specific expression pattern, were studied in these blind mammals and in related species with normal eyes by hybridizing their genomic DNAs with probes obtained from cDNA clones for alpha A-, alpha B-, and beta Bp-crystallins from calf and gamma 3-crystallin from the rat. For all crystallin genes examined, the hybridization signals of mole and mole rat genomic DNA were comparable, respectively, with those of shrew and of rat and mouse, normal-vision representatives of the orders Insectivora and Rodentia. The expression of the crystallins at the protein level was tested by using antiserum specific for alpha-crystallin in immunofluorescence reactions on lens sections of mole and mole rat eyes and by using antisera against the beta- and gamma-crystallins on sections of the mole eye. All antisera gave positive fluorescence reactions exclusively with lens tissue of these blind mammals, indicating that the crystallins are still normally expressed despite the fact that these lenses have had no function in a visual process in these mammals for at least many million years. These findings apparently imply that some unknown selective advantage has conserved the crystallin genes and their expression after the loss of normal function of the lenses.

Adaptation, Physiological↗
PubMed1985

Mole rat hemoglobin: primary structure and evolutionary aspects in a second karyotype of Spalax ehrenbergi, Rodentia, (2n = 52).

The hemoglobins of the four karyotypes of Spalax ehrenbergi (2n = 52, 54, 58, 60) did not show any differences in their electrophoretic pattern and in high performance liquid chromatography. The complete amino-acid sequence of mole rat hemoglobin (Spalax ehrenbergi), chromosome species 2n = 52, is presented. It was elucidated by automatic Edman degradation of the chains, the tryptic peptides, and the C-terminal peptide obtained by acid hydrolysis of the Asp-Pro bond in beta-chains. The alpha- and beta-chains are identical with those of the chromosome species 2n = 60. A comparison of the hemoglobins of mole rat, mouse, and other rodents shows homology but no indication of adaptation to subterranean life. In all probability alpha 11(A9)Arg and alpha 120(H3)Gly, unique in mole rat among all mammalian hemoglobins, are not involved in high oxygen affinity. The construction of a phylogenetic tree by the maximum parsimony method, based on hemoglobin sequences, made it possible to show that Rodentia originated as a monophyletic clade, and to find the phylogenetic relationship of Spalacidae to other Rodentia (Mus, Rattus, Ondatra, Mesocricetus, Citellus, and Cavia). Among all rodents the slowest rate of nucleotide replacements occurred in the lineage to Spalax (20%) and the fastest in the lineage to Cavia (59%).

Amino Acid Sequence↗
PubMed1984

Adaptive respiratory variation in 4 chromosomal species of mole rats.

Oxygen and carbon dioxide pressures were measured in subcutaneous gas pockets of 4 chromosomal species of the Spalax ehrenbergi complex. Oxygen pressures of 11.8, 13.6, 16.9, and 17.2 torr and CO2 pressures of 84.2, 82.9, 80.1, and 64.1 torr were measured for the chromosomal species 2n = 52, 54, 58, and 60, respectively. The differences between the 4 chromosomal species in their subcutaneous gas tension appear to reflect adaptive respiratory variation associated with geographic variation in climate. It underlies an important respiratory physiological correlate of ecological speciation in the extremely hypoxic and hypercapnic subterranean environment.

Animals↗
PubMed1984

Photoperiod perception in the blind mole rat (Spalax ehrenbergi, Nehring): involvement of the Harderian gland, atrophied eyes, and melatonin.

The involvement of the Harderian gland, atrophied eyes, and melatonin in the perception of photoperiodic changes has been studied in the mole rat, a fossorial blind mammal the thermoregulatory capacity of which is photoperiod-dependent. When transferred from a long photoperiod to a short one, mole rats increase their resistance to cold, a perfectly reversible phenomenon. After 2 weeks under short photoperiod the thermoregulatory capacities of animals without Harderian glands are less than those of the controls. The Harderian gland appears thus to be implicated in the detection of photoperiodic changes. After 5 weeks, however, the Harderianectomized animals had perfectly integrated the photoperiodic change, so demonstrating that other photoreceptor organs exist. The atrophied eyes, which, under these conditions, do not seem to play an important role, are involved when the animals are transferred from short photoperiod to long photoperiod. Melatonin, but not 5-methoxytryptamine, appears to be a crucial compound in such a phenomenon. These results, which demonstrate that in mammals (at least in the mole rat, as in nonmammalian vertebrates), nonocular photoreceptors exist, suggest that the mechanism by which mammals integrate photoperiodic changes is not the same when the animals are transferred from long to short photoperiod as when transferred from short photoperiod to long photoperiod.

5-Methoxytryptamine↗
PubMed1984

Major histocompatibility complex of the mole-rat. I. Serological and biochemical analysis.

The mole-rat, Spalax ehrenbergi, is a complex subterranean rodent species whose habitat is restricted largely to the Middle East and North Africa. We typed over 50 mole-rats with mouse monoclonal and polyclonal antibodies specific for class I and class II major histocompatibility complex (Mhc) molecules. Some of these antibodies were produced against mouse Mhc molecules, others against Mhc molecules of other species. About 25% of the antibodies reacted with mole-rat lymphocytes in the cytotoxic test. Some of the serologically positive antibodies precipitated from a glycoprotein pool of mole-rat spleen cell molecules that corresponded in size with class I and class II molecules of other species. We conclude, therefore, that mole-rats, like other mammals, possess the Mhc which consists of class I and class II loci. We call this Mhc Spalax major histocompatibility (Smh) complex. The occurrence of a large number of different serotypes among the tested animals suggests that Smh loci are polymorphic. This Mhc polymorphism of the mole-rat contrasts with the monomorphism or oligomorphism of the Syrian hamster, a rodent with a similar ecology. Thus far no qualitative correlation could be found between Smh polymorphism and chromosome variation described in this superspecies.

Animals↗
PubMed1984

Biochemical diversity and evolution in the genus Mus.

Thirteen biochemical groups of wild mice from Europe, Asia, and Africa belonging to the genus Mus are analyzed at 22-42 protein loci. Phylogenetic trees are proposed and patterns of biochemical evolution are discussed, as well as the possible contribution of wild mice to the genetic diversity of laboratory stocks.

Alleles↗
PubMed1984

Differential viability of phosphoglucose isomerase allozyme genotypes of marine snails in nonionic detergent and crude oil-surfactant mixtures.

The effects of a nonionic detergent and of crude oil-detergent mixtures in aqueous solutions on the allozyme frequencies of phosphoglucose isomerase (Pgi) genotypes were tested in the Mediterranean marine gastropods Monodonta turbinata and M. turbiformis. Our results indicate differential survivorship of electrophoretical Pgi allozyme genotypes for both detergent alone and for crude oil-detergent mixtures. These results reflect the adaptive nature of some Pgi genotypes in these marine gastropods and seem inconsistent with the neutral theory of allozyme polymorphisms. Furthermore, these findings suggest that allozyme variants demonstrate a differential tolerance to these organic pollutants and can, therefore, be used as detectors of organic pollutants in the sea.

Animals↗
PubMed1984

Mercury selection of allozymes in marine organisms: Prediction and verification in nature.

The geographic distributions of mercury-tolerant allozyme genotypes of the enzyme phosphoglucomutase in the shrimp Palaemon elegans and the enzyme phosphoglucose isomerase in the marine gastropod Monodonta turbinata were compared in a mercury-polluted site versus several unpolluted sites on the Israeli coast of the Mediterranean sea. We conclude that in both phosphoglucomutase and phosphoglucose isomerase, the level of the mercury-tolerant allozyme genotypes was higher in the polluted as compared with the unpolluted sites. These results suggest that mercury selection is operating in nature on allozyme genotypes of these marine organisms along patterns comparable with those found previously in laboratory experiments. We suggest that the enzymes studied here display an adaptive pattern in polluted environments. Therefore, they may be used as potential indicators and monitors of marine pollution.

Journal Article↗
PubMed1984

The primary structure of the hemoglobin of the mole rat (Spalax ehrenbergi, rodentia, chromosome species 60).

Mole rat (Spalax ehrenbergi) hemoglobin consists of only one component. The complete amino-acid sequence of the alpha- and beta-chains of the species with the diploid chromosome number of 60 is presented. Following chain separation by chromatography on carboxymethyl cellulose CM-52, the primary structures were established by automatic Edman degradation on the chains, on the tryptic peptides, and on a peptide obtained by acid hydrolysis of the Asp-Pro bond in beta-chains. The alignment of the peptides was performed by homology with human alpha- and beta-chains. The comparison showed an exchange of 23 residues in the alpha-chains and 26 in the beta-chains. One substitution in the beta-chains concerns the surrounding of the heme. We found two exchanges in each chain in the alpha 1 beta 1-subunit interface and one in the beta-chain alpha 1 beta 2-contact points. Though all binding sites for 2,3-bisphosphoglycerate are unchanged, the mole rat blood has a high oxygen affinity as a part of adaptation to subterranean life under hypoxia and hypercapnia. A comparison of the sequence with known X-ray models of hemoglobins may give an interpretation of this fact. The primary structure of the mole rat hemoglobin shows more similarities with surface rodents, than with the mole, another small mammal, adapted to hypoxia in subterranean tunnels. The adaptation to hypoxia in mole rat and mole must be due to different mechanisms.

Amino Acid Sequence↗
PubMed1983

Photoperiodic effects on thermoregulation in a 'blind' subterranean mammal.

Thermoregulatory responses to changes in photoperiod were studied in the 'blind' mole rat Spalax ehrenbergi (Nehring). Acclimation of cold-sensitive individuals to short photoperiod (8L:16D) at an ambient temperature (Ta) of 22 degrees C increased their thermoregulatory capacity in cold conditions, when compared to individuals which were acclimated to a photoperiod of 12L:12D at the same Ta. Acclimation of cold-resistant individuals to Ta = 17 degrees C but with a photoperiod of 16L:8D caused a decrease in thermoregulatory capacity. Evaluation of the visual pathway through the visual-evoked potentials showed that the mole rat does not respond to flash stimuli and can thus be considered to be effectively blind.

Animals↗
PubMed1983

Selection of allelic isozyme polymorphisms in marine organisms: pattern, theory, and application.

The evolutionary significance of allelic isozyme polymorphisms in several Mediterranean marine organisms was tested initially by post-hoc gene frequency analyses at 11-15 gene loci in natural populations of barnacles, Balanus amphitrite, under thermal [Nevo et al, 1977] and chemical [Nevo et al, 1978] pollutions. We next carried out pre-hoc controlled laboratory experiments to test the effects of heavy metal pollution (Hg, Zn, Cd) on genotypic frequencies of 15 phosphoglucomutase (PGM) genotypes in thousands of individuals of the shrimp Palaemon elegans [Nevo et al, 1980, 1981a, and the present study]. Similarly, we tested the effects of Hg, Zn, Cd, Pb, Cu pollutions on the genotypic and allelic frequencies of five phosphoglucose isomerase (PGI) genotypes in the two close species of marine gastropods, Monodonta turbinata and M turbiformis [Lavie and Nevo, 1982, and the present study]. In both the thermal and chemical pollution studies, we established in repeated experiments statistically significant differences of allele frequencies at 8 out of 11 (73%) and 10 out of 15 (67%) gene loci, respectively, between the contrasting environments in each. While no specific function could be singled out in the post-hoc chemical study due to the complex nature of polluted marine water, temperature could be specified as the primary selective agent in the thermal study. The strongest direct and specific evidence for significant differential survivorship among allelic isozyme genotypes was obtained in the pre-hoc studies in Palaemon and Monodonta. Their differential viability was probably associated with the different degree of heavy metal inhibition uniquely related to each specific pollutant. Furthermore, we demonstrated in the two closely related Monodonta species parallel genotypic differentiation as a response to pollution. Our results are inconsistent with the neutral theory of allelic isozyme polymorphisms and appear to reflect the adaptive nature of the allelic isozyme polymorphisms studied. Allelic isozyme genotypes are sensitive to and vary with the quality and quantity of specific pollutants. Therefore, they can provide precise genetic indicators of the effects of pollution on the short- and long-term genetic changes of populations. Ideally, in different marine species specific genetic loci, either singly or in combination, may prove sensitive markers to different pollutants and could easily be assayed by quick electrophoretic tests and be used as genetic monitors. An extensive search for the appropriate enzymatic systems in various relatively sedentary marine species exposed to pollutants is therefore urgent.

Adaptation, Physiological↗
PubMed1980

Preliminary investigations of melatonin and 5-methoxy-tryptophol synthesis in the pineal, retina, and harderian gland of the mole rat and in the pineal of the mouse "eyeless".

Hydroxyindole-O-methyltransferase (HIOMT) activity for the synthesis of melatonin and 5-methoxytryptophol, both 5-methoxyindoles, was measured in the pineal, the Harderian gland and the retina of the mole rat and in the pineal of the mouse "eyeless". In the pineal and the Harderian gland of the mole rat a larger amount of 5-methoxytryptophol than of the melatonin is synthesized. 5-Methoxyindole synthesis is extremely high in the Harderian gland, whereas in the retina HIOMT activity is low and variable. In the pineal of the mouse "eyeless", a low 5-methoxyindole synthesis showing no circadian rhythm is demonstrated. It is concluded that, besides the generally accepted regulation of the indole metabolism by light, in species with atrophied eyes having Harderian glands (mole rat) and in species without eyes other factors than light might be responsible for the indole metabolism in the pineal gland.

Acetylserotonin O-Methyltransferase↗
PubMed1976

Assortative mating between chromosome forms of the mole rat, Spalax ehrenbergi.

Females of two parapatric chromosomal forms (2n = 52 and 2n =58) of the fossorial mole rat, Spalax ehrenbergi, in Israel, were tested for mate selection between two alternative, a homo- and a heterochromosomal, males. Estrous females significantly preferred the male of their own chromosomal form, on the basis of several behavioural criteria. The evolutionary significance of the positive assortative mating found, lies presumably in reinforcing reproductive isolation between the chromosome forms, thereby contributing to finalize speciation.

Animals↗
PubMed1976

Olfactory discrimination as an isolating mechanism in speciating mole rats.

Olfactory discrimination was tested in two chromosome forms of the speciating fossorial rodent, Spalax ehrenbergi, in Israel. Females of the chromosome forms 2n = 52 and 2n = 58 were tested for male odour discrimination, the source of odour being either case litter or urine. Estrous females of both forms preferred homochromosomal odurs, whereas diestrous females showed no discrimination. These results suggest that olfactory discrimination may serve as a reproductive isolating mechanism in the speciation of mole rats.

Animals↗