Interpretation of calcifications in screen/film, digitized, and wavelet-enhanced monitor-displayed mammograms: a receiver operating characteristic study.

RATIONALE AND OBJECTIVES: The acceptance of filmless digital mammography is currently limited by digitization and display drawbacks, as well as bias toward hard-copy interpretation. In the current study, we evaluated a wavelet-based image enhancement method for the filmless interpretation of breast calcifications. METHODS: A set of 100 mammograms (58 with calcification clusters) was digitized at 105 microns and 4,096 gray levels per pixel and was processed with nonlinear filters and wavelets. Standard receiver operating characteristic analysis was performed by four radiologists, who independently read the films, the unprocessed digital images, and unprocessed and wavelet-enhanced digital images presented simultaneously. RESULTS: Statistical differences were observed between screen/film and unprocessed digitized mammography displayed on monitors. Differences were not significant when wavelet enhancement was included in the monitor display. Interobserver variation in the digitized reading was greater than in film reading, but the wavelet enhancement reduced the difference. CONCLUSION: Wavelet-enhanced digital mammograms may assist radiologists in diagnosing calcifications directly from computer monitors and may compensate for current technologic limitations. A study with a larger data-base is needed before this method is accepted for clinical use.

Mitochondrial DNA evolution in mice.

This study extends knowledge of mitochondrial DNA (mtDNA) diversity in mice to include 208 animals belonging to eight species in the subgenus Mus. Highly purified mtDNA from each has been subjected to high-resolution restriction mapping with respect to the known sequence of one mouse mtDNA. Variation attributed to base substitutions was encountered at about 200 of the 300 cleavage sites examined, and a length mutation was located in or near the displacement loop. The variability of different functional regions in this genome was as follows, from least to most: ribosomal RNA, transfer RNA, known proteins, displacement loop and unidentified reading frames. --Phylogenetic analysis confirmed the utility of the Sage and Marshall revision of mouse classification, according to which there are at least four species of commensal mice and three species of aboriginal mice in the complex that was formerly considered to be one species. The most thoroughly studied of these species is Mus domesticus, the house mouse of Western Europe and the Mediterranean region, which is the mitochondrial source of all 50 of the laboratory strains examined and of the representatives of wild house mice introduced by Europeans to North and South America during the past few hundred years. --The level of mtDNA variation among wild representatives of M. domesticus is similar to that for the Eastern European house mouse (M. musculus) and several other mammalian species. By contrast, among the many laboratory strains that are known or suspected to stem from the pet mouse trade, there is little interstrain variation, most strains having the "old inbred" type of domesticus mtDNA, whose frequency in the 145 wild mice examined is low, about 0.04. Also notable is the apparent homogeneity of mtDNA in domesticus races that have fixed six or more fused chromosomes and the close relationship of some of these mtDNAs to those of karyotypically normal mice. --In addition, this paper discusses fossil and other evidence for the view that in mice, as in many other mammals, the average rate of point mutational divergence in mtDNA is 2-4% per million years. From this, it is estimated that the commensal association between mice and our ancestors began more than a million years ago, i.e., at an early stage in the evolution of Homo erectus.

Unusual type of mitochondrial DNA in mice lacking a maternally transmitted antigen.

Mice that lack a maternally transmitted antigen (Mta) on the cell surface share a distinctive type of mitochondrial DNA. This is evident from restriction analyses of mitochondrial DNAs from 25 strains of mice whose antigenic state is known. One hundred sixty-eight cleavage sites have been mapped in the mitochondrial DNA of Mta- mice. Detailed maps for the 8 other types of mitochondrial DNA detected in the survey have also been prepared. The Mta- mice are estimated to differ from those expressing the antigen by 108 to 141 base substitutions at widely scattered points in the mitochondrial genome.

Flow of mitochondrial DNA across a species boundary.

Restriction analysis shows that wild Scandinavian mice belonging to the species Mus musculus contain the mitochondrial DNA of a neighboring species, M. domesticus. This demonstration results from comparisons of Scandinavian mice with authentic M. domesticus and M. musculus from other parts of Europe. Electrophoretic and immunological analysis of eight diagnostic proteins confirms that mice from north of the hybrid zone in Denmark are M. musculus in regard to their nuclear genes. In contrast, the mice tested from this region and a nearby part of Sweden have exclusively M. domesticus types of mitochondrial DNA. Phylogenetic analysis of the restriction maps suggests that the mitochondrial DNAs found in Scandinavian M. musculus could stem from a single M. domesticus female.

Radiation of human mitochondria DNA types analyzed by restriction endonuclease cleavage patterns.

Human mitochondrial DNA (mtDNA) restriction endonuclease fragment patterns were analyzed using total blood cell DNA isolated from 200 individuals representing five different populations. Thirty-two fragment patterns (morphs) were observed with the enzymes Hpa I, Bam HI, Hae II, Msp I and Ava II yielding thirty-five different combinations of fragment patterns (mt DNA types). The major ethnic groups exhibit quantitative as well as qualitative differences in their mtDNA types, all of which are related to each other by a tree in which the closely related mtDNA types cluster according to geographic origin. Three mtDNA types are postulated to be 'central' to ethnic radiations due to their high frequencies, their appearance in more than one ethnic group, or their presence in other primate species. Genetic distances among populations were computed and employed in construction of an average linkage tree. If one of the three central mtDNA types is the root of the tree, differences in evolutionary rates among the branches become apparent. In particular, the Bushmen appear to have a higher evolutionary rate for mtDNA than the other four populations. Comparisons with nuclear gene frequencies suggest that this higher evolutionary rate may be the product of an elevated mutation rate or fixation of mutations in mtDNA.

Extensive polymorphism in the mitochondrial DNA of apes.

Ape species are 2-10 times more variable than the human species with respect to the nucleotide sequence of mtDNA, even though ape populations have been smaller than the human population for at least 10,000 years. This finding was made by comparing purified mtDNAs from 27 individuals with the aid of 25 restriction endonucleases; for an additional 59 individuals, comparisons were made with fewer enzymes by using the blot hybridization method. The amount of intraspecific sequence divergence was greatest between orangutans of Borneo and Sumatra. Among common chimpanzees, a large component of the variation is due to two highly distinct forms of mtDNA that may reflect a major geographic subdivision. The least amount of sequence variation occurred among lowland gorillas, which exhibit only twice as much sequence variation as humans. The large intraspecific differences among apes, together with the geological and protein evidence, leads us to propose that each ape species is the remnant of an ancient and widespread population that became subdivided geographically and reduced in size and range, perhaps by hominid competition. The low variation among human mtDNAs is consistent with geological evidence that the human species is young. The distribution of site changes within the mitochondrial genome was also examined. Comparison of closely related mtDNAs shows that the ribosomal RNA genes have diverged more slowly than the rest of the genome.

Evolutionary tree for apes and humans based on cleavage maps of mitochondrial DNA.

The high rate of evolution of mitochondrial DNA makes this molecule suitable for genealogical research on such closely related species as humans and apes. Because previous approaches failed to establish the branching order of the lineages leading to humans, gorillas, and chimpanzees, we compared human mitochondrial DNA to mitochondrial DNA from five species of ape (common chimpanzee, pygmy chimpanzee, gorilla, orangutan, and gibbon). About 50 restriction endonuclease cleavage sites were mapped in each mitochondrial DNA, and the six maps were aligned with respect to 11 invariant positions. Differences among the maps were evident at 121 positions. Both conserved and variable sites are widely dispersed in the mitochondrial genome. Besides site differences, ascribed to point mutations, there is evidence for one rearrangement: the gorilla map is shorter than the other owing to the deletion of 95 base pairs near the origin of replication. The parsimony method of deriving all six maps from a common ancestor produced a genealogical tree in which the common and pygmy chimpanzee maps are the most closely related pair; the closest relative of this pair is the gorilla map; most closely related to this trio is the human map. This tree is only slightly more parsimonious than some alternative trees. Although this study has given a magnified view of the genetic differences among humans and apes, the possibility of a three-way split among the lineages leading to humans, gorillas, and chimpanzees still deserves serious consideration.

Evolution of the differential regulation of duplicate genes after polyploidization.

In the 50 million years since the polyploidization event that gave rise to the catostomid family of fishes the duplicate genes encoding isozymes have undergone different fates. Ample opportunity has been available for regulatory evolution of these duplicate genes. Approximately half the duplicate genes have lost their expressions during this time. Of the duplicate genes remaining, the majority have diverged to different extents in their expression within and among adult tissues. The pattern of divergence of duplicate gene expression is consistent with the accumulation of mutations at regulatory genes. The absence of a correlation of extent of divergence of gene expression with the level of genetic variability for isozymes at these loci is consistent with the view that the rates of regulatory gene and structural gene evolution are uncoupled. The magnitude of divergence of duplicate gene expressions varies among tissues, enzymes, and species. Little correlation was found with the extent of divergence of duplicate gene expression within a species and its degree of morphological "conservatism", although species pairs which are increasingly taxonomically distant are less likely to share specific patterns of differential gene expression. Probable phylogenetic times of origin of several patterns of differential gene expression have been proposed. Some patterns of differential gene expression have evolved in recent evolutionary times and are specific to one or a few species, whereas at least one pattern of differential gene expression is present in nearly all species and probably arose soon after the polyploidization event. Multilocus isozymes, formed by polyploidization, provide a useful model system for studying the forces responsible for the maintenance of duplicate genes and the evolution of these once identical genes to new spatially and temporally specific patterns of regulation.

Genetic and molecular analysis of nonrandom dimer assembly of the creatine kinase isozymes of fishes.

Species within many families of actinopterygian bony fishes (class Osteichthyes) have a two-banded allelic isozyme phenotype in individuals heterozygous at the creatine kinase A locus. This two-banded pattern is formed by the presence of the two homodimeric isozymes and the absence of the expected heterodimer. Sharks and amphibians have retained the ability to form all three allelic isozymes in individuals which are heterozygous. Reversible denaturation procedures were able to assemble the different allelic CK-A subunits within a species to form CK-A2 heterodimers. Furthermore, heterodimers were formed from different CK-A subunits from highly divergent species after this in vitro molecular hybridization process. It is concluded from these studies that the polypeptide-binding sites of creatine kinase are structurally conservative in most fishes and that the absence of a heterodimer in heterozygous individuals is not due to a structural incompatibility between the different A subunit types or to an instability of the heterodimer during electrophoresis. A temporal and/or spatial isolation of allelic CK-A subunit synthesis and assembly, within differentiated skeletal muscle, appears to have evolved in the actinopterygian bony fishes.

Duplicate gene expression in diploid and tetraploid loaches (Cypriniformes, Cobitidae).

Botia macracantha and B. modesta have been demonstrated to be tetraploid species on the basis of their karyotypes and on the basis of the expression of a number of isozymes encoded by duplicate loci. A rather low percentage of duplicate loci was detected by electrophoresis, compared to that for other tetraploid Cypriniformes. Several hypotheses have been advanced to account for the low levels of duplicate gene expression observed. Lastly, many of the duplicate loci have diverged to unique patterns of expressions in different tissues or different levels of activity within a single tissue.