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Query: UNIPROT:P06889 (Mol)
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Genetic variation at the Major Histocompatibility Complex locus DQ beta was analyzed in 233 beluga whales (Delphinapterus leucas) from seven populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chukchi Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin Island, and High Arctic and in 12 narwhals (Monodon monoceros) sympatric with the High Arctic beluga population. Variation was assessed by amplification of the exon coding for the peptide binding region via the polymerase chain reaction, followed by either cloning and DNA sequencing or single-stranded conformation polymorphism analysis. Five alleles were found across the beluga populations and one in the narwhal. Pairwise comparisons of these alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per site leading to eight amino acid differences, five of which were nonconservative substitutions, centered around positions previously shown to be important for peptide binding. Although the amount of allelic variation is low when compared with terrestrial mammals, the nature of the substitutions in the peptide binding sites indicates an important role for the DQ beta locus in the cellular immune response of beluga whales. Comparisons of allele frequencies among populations show the High Arctic population to be different (P < or = .005) from the other beluga populations surveyed. In these other populations an allele, Dele-DQ beta*0101-2, was found in 98% of the animals, while in the High Arctic it was found in only 52% of the animals. Two other alleles were found at high frequencies in the High Arctic population, one being very similar to the single allele found in narwhal.
Mol Biol Evol 1995 Jul
PMID:Sequence variation at the major histocompatibility complex locus DQ beta in beluga whales (Delphinapterus leucas) 765 14

Attempts to study the genetic population structure of large mammals are often hampered by the low levels of genetic variation observed in these species. Polar bears have particularly low levels of genetic variation with the result that their genetic population structure has been intractable. We describe the use of eight hypervariable microsatellite loci to study the genetic relationships between four Canadian polar bear populations: the northern Beaufort Sea, southern Beaufort Sea, western Hudson Bay, and Davis Strait-Labrador Sea. These markers detected considerable genetic variation, with average heterozygosity near 60% within each population. Interpopulation differences in allele frequency distribution were significant between all pairs of populations, including two adjacent populations in the Beaufort Sea. Measures of genetic distance reflect the geographic distribution of populations, but also suggest patterns of gene flow which are not obvious from geography and may reflect movement patterns of these animals. Distribution of variation is sufficiently different between the Beaufort Sea populations and the two more eastern ones that the region of origin for a given sample can be predicted based on its expected genotype frequency using an assignment test. These data indicate that gene flow between local populations is restricted despite the long-distance seasonal movements undertaken by polar bears.
Mol Ecol 1995 Jun
PMID:Microsatellite analysis of population structure in Canadian polar bears. 766 52

The production of myelin by oligodendrocytes requires the coordinated, massive synthesis of myelin components, a program that is dependent on transcriptional controls. Myelin transcription factor I (MyTI) was named for its ability to recognize the proteolipid protein (PLP) gene, the most abundantly transcribed central nervous system myelin gene (Kim and Hudson: Mol. Cell Biol. 12:5632, 1992). MyTI is a zinc-dependent, DNA-binding protein of the Cys2-His-Cys class. The pattern of MyTI expression, documented in the present study, suggests that MyTI may be instrumental in early stages of oligodendrocytic development and myelin production. MyTI mRNA transcripts are more highly expressed in oligodendrocyte progenitors than in differentiated oligodendrocytes. In vitro and in vivo analyses show that MyTI immunoreactivity is stronger in oligodendrocytic progenitors than in mature oligodendrocytes which have already accumulated PLP. In oligodendrocyte progenitors, MyTI immunoreactivity appears as speckles within the nucleus, suggestive of an association of MyTI with a function that is spatially segregated into discrete nuclear domains. MyTI continues to be expressed in cells transcribing PLP. However, as oligodendrocytes accumulate PLP, MyTI immunoreactivity becomes restricted to the cytoplasm and progressively diminishes. Since MyTI has two widely separated sets of DNA-binding domains and initial MyTI expression markedly precedes PLP expression, we hypothesize the following model: MyTI may play a role in assembling transcriptionally active complexes of PLP, perhaps by bending the DNA of the promoter region to induce an appropriate conformation to enable subsequent binding of additional regulatory proteins.
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PMID:Expression of myelin transcription factor I (MyTI), a "zinc-finger" DNA-binding protein, in developing oligodendrocytes. 853 Jan 87

We surveyed nucleotide sequence variation at glucose dehydrogenase (Gld), in a region of low recombination on chromosome 3R, from a population sample of Drosophila simulans. The levels of nucleotide variation were surprisingly high. There was no departure from the expectation of a neutral model for the level of polymorphism, indicating no evidence of a selective sweep in this region. There was a significant deficiency of singleton polymorphisms according to the Fu and Li test, although Tajima and Hudson, Kreitman, and Aguade (HKA) tests do not provide evidence of a significant elevation of variation due to balancing selection. Genetic map data for the D. simulans third chromosome were used to calculate expected values of pi for Gld under a current model of background selection, varying the values for the parameter sh (selection coefficient against deleterious mutations). We show that the recombinational landscape of D. simulans is sufficiently different from that of D. melanogaster that we expect higher variation under the background selection model, even when effective population sizes are assumed to be equal. The data for Gld were tested against the predictions using computer simulations of the distribution of the number of segregating sites conditioned on pi. Background selection alone can explain our observations as long as sh is larger than 0.005 and species-level effective population size is assumed to be several-fold larger than in D. melanogaster. Alternatively, the deleterious mutation rate may be smaller in D. simulans, or balancing selection may be acting nearby, thereby reducing the effect of background selection.
Mol Biol Evol 1996 Oct
PMID:High nucleotide sequence variation in a region of low recombination in Drosophila simulans is consistent with the background selection model. 886 67

The North American beluga whale Delphinapterus leucas population has been divided into a number of putative geographical stocks based upon migration routes and areas of summer concentration. Nucleotide sequences of the mitochondrial DNA (mtDNA) control region were used to assess whether these geographical stocks are genetically distinct. Beluga whale samples from 25 sites were collected primarily from aboriginal subsistence hunts across North America from 1984 to 1994. Thirty-nine mtDNA haplotypes were identified in 628 beluga samples. No differences were found in the distribution of haplotypes between male and female beluga whales at any sampling site. These haplotypes segregated into two distinct assemblages in both a haplotype network and a neighbour-joining tree. The haplotype assemblages and a geographically disjunct distribution that suggests postglacial recolonization of the North American Arctic from two different refugia. An analysis of molecular variance based on haplotype relationships and frequency indicated genetic heterogeneity among beluga whale summering groups (P < or = 0.001). Sequence divergence estimates between sampling sites also indicated geographical differentiation, particularly between samples taken at east Hudson Bay or St Lawrence River and the western or central Arctic. The results of this study show a high degree of philopatry to specific summering areas by this highly mobile animal.
Mol Ecol 1997 Nov
PMID:Matriarchal genetic population structure of North American beluga whales Delphinapterus leucas (Cetacea: Monodontidae). 939 62

Beluga whales (Delphinapterus leucas) in North American waters migrate seasonally between wintering areas in broken pack ice and summering locations in estuaries and other open water areas in the Arctic and sub-Arctic. Results from our previous investigation of beluga whale mitochondrial DNA (mtDNA) revealed genetic heterogeneity among beluga from different summering locations that was interpreted as representing a high degree of summering site philopatry. However, mtDNA is maternally inherited and does not reflect mating that may occur among beluga from different summering locations in wintering areas or during annual migrations. To test the possibility that breeding occurs among beluga from different summering locations, genetic variability at five nuclear DNA (nDNA) microsatellite loci was examined in the same animals tested in the mtDNA study. Beluga samples (n = 640) were collected between 1984 and 1994 from 24 sites across North America, mostly during the summer. Whales from the various sites were categorized into eight summering locations as identified by mtDNA analysis, as well as four hypothesized wintering areas: Bering Sea, Hudson Strait (Hudson Strait, Labrador Sea, southwest Davis Strait), Baffin Bay (North Water, east Davis Strait), and St Lawrence River. Microsatellite allele frequencies indicated genetic homogeneity among animals from summering sites believed to winter together but differentiation among whales from some of the wintering areas. In particular, beluga from western North America (Bering Sea) were clearly distinguished from beluga from eastern North America (Hudson Strait, Baffin Bay, and St Lawrence River). Based upon the combined data set, the population of North American beluga whales was divided into two evolutionarily significant units. However, the population may be further subdivided into management units to reflect distinct groups of beluga at summering locations.
Mol Ecol 1999 Mar
PMID:Population structure of North American beluga whales (Delphinapterus leucas) based on nuclear DNA microsatellite variation and contrasted with the population structure revealed by mitochondrial DNA variation 1019 5

Polo kinases execute multiple roles during cell division. The fission yeast polo related kinase Plo1 is required to assemble the mitotic spindle, the prophase actin ring that predicts the site for cytokinesis and for septation after the completion of mitosis (Ohkura et al., 1995; Bahler et al., 1998). We show that Plo1 associates with the mitotic but not interphase spindle pole body (SPB). SPB association of Plo1 is the earliest fission yeast mitotic event recorded to date. SPB association is strong from mitotic commitment to early anaphase B, after which the Plo1 signal becomes very weak and finally disappears upon spindle breakdown. SPB association of Plo1 requires mitosis-promoting factor (MPF) activity, whereas its disassociation requires the activity of the anaphase-promoting complex. The stf1.1 mutation bypasses the usual requirement for the MPF activator Cdc25 (Hudson et al., 1990). Significantly, Plo1 associates inappropriately with the interphase SPB of stf1.1 cells. These data are consistent with the emerging theme from many systems that polo kinases participate in the regulation of MPF to determine the timing of commitment to mitosis and may indicate that pole association is a key aspect of Plo1 function. Plo1 does not associate with the SPB when septation is inappropriately driven by deregulation of the Spg1 pathway and remains SPB associated if septation occurs in the presence of a spindle. Thus, neither Plo1 recruitment to nor its departure from the SPB are required for septation; however, overexpression of plo1+ activates the Spg1 pathway and causes transient Cdc7 recruitment to the SPB and multiple rounds of septation.
Mol Biol Cell 1999 Aug
PMID:Plo1 kinase recruitment to the spindle pole body and its role in cell division in Schizosaccharomyces pombe. 1043 27

In order to assess levels of major histocompatibility complex (Mhc) variation within the St Lawrence beluga (Delphinapterus leucas) the variation at the beluga Mhc DRB1 class II locus was assessed by single-strand conformation polymorphism (SSCP) analysis of the peptide-binding region for 313 whales collected from 13 sampling locations across North America. In addition, samples from west Greenland and the St Lawrence were also typed at the DQB locus, allowing comparison to a previous study and assessment of linkage disequilibrium of alleles at the two loci. Comparisons of DRB1 and DQB allele frequencies among all sampling locations indicated genetic structure (alpha < 0.005). Most of this structure resulted from differences between the different wintering groups. Significant genetic structure (alpha = 0.05) exists among each pair of the following groups at both the DRB1 and DQB loci; St Lawrence, Hudson Strait, Bering Sea, Cunningham Inlet, and Davis Strait (minus Cunningham Inlet), except the St Lawrence and Hudson Strait for the DQB locus. In the St Lawrence population, six of the eight DRB1 alleles are present representing all five known allelic lineages. Evidence of linkage disequilibrium between the DRB1 and DQB is present in two sampling locations, the St Lawrence and Nuussuaq (alpha = 0.05). Analysis of probable DRB1-DQB haplotypes among groups of beluga suggests a haplotype reduction in the St Lawrence.
Mol Ecol 1999 Jul
PMID:Allelic and haplotype variation of major histocompatibility complex class II DRB1 and DQB loci in the St Lawrence beluga (Delphinapterus leucas). 1044 54

Despite extensive knowledge of many muscle A-band proteins (myosin molecules, titin, C-protein (MyBP-C)), details of the organization of these molecules to form myosin filaments remain unclear. Recently the myosin head (crossbridge) configuration in a relaxed vertebrate muscle was determined from low-angle X-ray diffraction (Hudson et al. (1997), J Mol Biol 273: 440-455). This showed that, even without C-protein, the myosin head array displays a characteristic polar pattern with every third 143 A-spaced crossbridge level particularly prominent. However, X-ray diffraction cannot determine the polarity of the crossbridge array relative to the neighbouring actin filaments; information crucial to a proper understanding of the contractile event. Here, electron micrographs of negatively-stained goldfish A-segments and of fast-frozen, freeze-fractured plaice A-bands have been used to determine the resting myosin head polarity relative to the M-band. In agreement with the X-ray data, the prominent 429 A-spaced striations are seen outside the C-zone, where no non-myosin proteins apart from titin are thought to be located. The head orientation is with the concave side of the curved myosin heads (containing the entrance to the ATP-binding site) facing towards the M-band and the convex surface (containing the actin-binding region at one end) facing away from the M-band.
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PMID:A-band architecture in vertebrate skeletal muscle: polarity of the myosin head array. 1122 95

The comparative molecular phylogeography of regional fish fauna has revealed the wide distribution of young clades in freshwater fishes of formerly glaciated areas as well as interspecific incongruences in their refugial origins and recolonization routes. In this study, we employed single-strand conformation polymorphism (SSCP) and sequence analyses to describe mitochondrial DNA (mtDNA) polymorphism among 27 populations of the lake cisco (Coregonus artedi) from its entire range of distribution in order to evaluate the hypothesis of dual glacial refuges proposed by Bernatchez & Dodson against the traditional view that this species is solely of Mississippian origin. Results indicate that this taxon is composed of two closely related groups that are widely distributed and intermixed over most of the sampled range. The estimated level of divergence (0.48%), the contrast in the geographical distribution of each group, as well as the general distribution of C. artedi in North America together support the hypothesis that one group dispersed from a Mississippian refuge via the proglacial lakes, while the other is of Atlantic origin and also took advantages of earlier dispersal routes towards eastern Hudson Bay drainages. However, the signal of past range fragmentation revealed by a nested clade analysis was weak, and did not allow to formally exclude the hypothesis of a single Mississippian origin for both lineages. Comparisons with the phylogeographic patterns of other Nearctic freshwater fishes suggest that the salinity tolerance and thermal sensitivity of lake cisco may have been determinant for its extensive postglacial dispersal. The presence or co-occurrence of sympatric or allopatric eco/morphotypes were not found to be necessarily associated with the presence of both haplotype groups.
Mol Ecol 2001 Apr
PMID:Mitochondrial DNA phylogeography of lake cisco (Coregonus artedi): evidence supporting extensive secondary contacts between two glacial races. 1134 5


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