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E P Lessa

Publications and source records attributed to E P Lessa.

7 recordsLinked to original sources
PubMed2001

Molecular evolution of Aldolase A pseudogenes in mice: multiple origins, subsequent duplications, and heterogeneity of evolutionary rates.

The Aldolase multigene family comprises three functional genes (A, B, and C) with tissue-specific expression regulated during ontogeny. DGGE analysis and nucleotide sequencing reveal a family of retropseudogenes of type A in species of MUS: Significant variation in rates of evolution of Aldolase A retropseudogenes is apparent. Our analyses demonstrate that (1) multiple events of retrotransposition are needed to account for the diversity of Aldolase A processed pseudogenes found in mice; (2) some of these sequences have undergone further duplication subsequent to the original retrotransposition event; (3) the patterns of nucleotide substitution are broadly comparable with previous estimates; and (4) estimates of rates of divergence for this array of sequences are up to four times higher than those reported in the literature.

Animals↗
PubMed2001

Recurrent amplifications and deletions of satellite DNA accompanied chromosomal diversification in South American tuco-tucos (genus Ctenomys, Rodentia: Octodontidae): a phylogenetic approach.

We investigated the relationship between satellite copy number and chromosomal evolution in tuco-tucos (genus Ctenomys), a karyotypically diverse clade of rodents. To explore phylogenetic relationships among 23 species and 5 undescribed forms, we sequenced the complete mitochondrial cytochrome b genes of 27 specimens and incorporated 27 previously published sequences. We then used quantitative dot-blot techniques to assess changes in the copy number of the major Ctenomys satellite DNA (satDNA), named RPCS. Our analysis of the relationship between variation in copy number of RPCS and chromosomal changes employed a maximum-likelihood approach to infer the copy number of the satellite RPCS in the ancestors of each clade. We found that amplifications and deletions of RPCS were associated with extensive chromosomal rearrangements even among closely related species. In contrast, RPCS copy number stability was observed within clades characterized by chromosomal stability. This example reinforces the suspected role of amplification, deletion, and intragenomic movement of satDNA in promoting extensive chromosomal evolution.

Animals↗
PubMed1998

The molecular phylogenetics of tuco-tucos (genus Ctenomys, Rodentia: Octodontidae) suggests an early burst of speciation.

Variation in the nucleotide sequence of the entire mitochondrial cytochrome b gene (1140 bp) was examined for 27 individuals representing 13 species of South American rodents of the genera Ctenomys, Octodontomys, Tympanoctomys, and Spalacopus. Representatives of the family Echimyidae, Euryzygomatomys and Mesomys, were used as outgroups to test the monophyly of the Octodontinae and Ctenomyinae. Relationships among species of tuco-tucos (genus Ctenomys) were also examined including representatives of the three described subgenera and the two sperm morphs. Reciprocal monophyly of the Octodontinae and Ctenomyinae is strongly supported. Several basal relationships among species of the genus Ctenomys are poorly resolved, suggesting the possibility of a hard polytomy due to a rapid and potentially simultaneous radiation early in the history of the genus. In other cases, clades within the Ctenomyinae previously identified on the basis of allozymes, chromosomes, parasites, or skull morphology were supported. Calibrations based on the fossil record suggest that the mitochondrial cytochrome b of these caviomorphs has evolved at a rapid rate, comparable to those proposed for Mus-Rattus, and three to four times higher than ungulate rates.

Animals↗
PubMed1993

Screening techniques for detecting allelic variation in DNA sequences.

This article reviews four 'DNA screening techniques', namely heteroduplex analysis, single-strand conformational polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) as tools for the study of allelic variation in natural populations. The resolving power, advantages, and limitations of each technique are discussed and compared. We also provide some criteria for choosing among techniques and illustrate some practical issues with examples taken primarily from our own laboratory experience.

Alleles↗
PubMed1992

Rapid surveying of DNA sequence variation in natural populations.

DNA sequencing can be costly and time consuming for population studies because of the relative rarity of variation along exons. These problems can be substantially reduced by the use of the polymerase chain reaction on introns using primers from the exon region. These problems can be further reduced by the use of denaturing gradient gel electrophoresis to identify those alleles in need of sequencing.

Animals↗
PubMed1990

Morphological evolution of subterranean mammals: integrating structural, functional, and ecological perspectives.

The widely recognized convergence of subterranean mammals offers unique opportunities for the study of patterns, causes and consequences of morphological integration. For example, behavioral and biomechanical observations have revealed a diversity of digging modes among subterranean mammals. In rodents, scratch-digging and chisel-tooth digging, alone or combined, are widespread. This dual nature of the digging apparatus must be understood to avoid erroneous assessments of specializations based on forelimb modifications only. Additionally, bulldozing and disposal of loose soil is performed by head-lifting, by means of the forelimbs, or with the hindlimbs. Insectivores are known to resort to scratch-digging, sand-swimming, or to a unique system known as humeral rotation. Semi-fossorial species among rodents and insectivores are scratch-diggers. In contrast, fully subterranean taxa show further specializations for scratch-digging and/or resort to some of the other digging modes. The ecological correlates of these morphological trends are still poorly known; work in geomyids suggests that scratch-digging specializations are efficient in friable soils, whereas tooth-digging allows the utilization of a much broader spectrum of soil types. This indicates that alternative pathways of morphological specialization are not equivalent in their ecological potentialities. Important morphological features, such as incisor procumbency among tooth-diggers, are shown to be constrained by structural, allometric, and mechanical factors. In geomyids, the same procumbent morphologies may be acquired as a byproduct of size increases, by means of adaptive shifts independent from size, or by a combination of both. Thus, geometric similarity may not be indicative of functional similarity. Further constraints result from the integration of different functions. For instance, it is suggested that mastication imposes limitations upon potential modifications of jaw morphology for tooth-digging. Scratch-digging appears to be less constrained by locomotion, but the effects of integration of various functions in fore- and hind-limbs are largely unexplored. Multiple approaches, combining behavioral, functional, ecological, structural, and phylogenetic data, are necessary for the study of morphological evolution among subterranean mammals.

Animals↗