Biomedical subjects

Richard von Sternberg

Publications and source records attributed to Richard von Sternberg.

3 recordsLinked to original sources

PubMed2005

Why repetitive DNA is essential to genome function.

There are clear theoretical reasons and many well-documented examples which show that repetitive, DNA is essential for genome function. Generic repeated signals in the DNA are necessary to format expression of unique coding sequence files and to organise additional functions essential for genome replication and accurate transmission to progeny cells. Repetitive DNA sequence elements are also fundamental to the cooperative molecular interactions forming nucleoprotein complexes. Here, we review the surprising abundance of repetitive DNA in many genomes, describe its structural diversity, and discuss dozens of cases where the functional importance of repetitive elements has been studied in molecular detail. In particular, the fact that repeat elements serve either as initiators or boundaries for heterochromatin domains and provide a significant fraction of scaffolding/matrix attachment regions (S/MARs) suggests that the repetitive component of the genome plays a major architectonic role in higher order physical structuring. Employing an information science model, the 'functionalist' perspective on repetitive DNA leads to new ways of thinking about the systemic organisation of cellular genomes and provides several novel possibilities involving repeat elements in evolutionarily significant genome reorganisation. These ideas may facilitate the interpretation of comparisons between sequenced genomes, where the repetitive DNA component is often greater than the coding sequence component.

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PubMed2003

Autapomorphies of the endophragmal system in trichodactylid freshwater crabs (Crustacea: Decapoda: Eubrachyura).

An examination of the thoracic endophragmal system in trichodactylid freshwater crabs revealed several derived features that appear restricted to this family. Trichodactylids have a highly reduced sella turcica with a rim-like overall configuration; as a consequence of sella turcica reduction the median septum is dorsoventrally diminished and exposed along its length. In addition, interosternite 7/8 is medially erased with the remnants restricted to the lateral regions of the sternum. The configurations of the sella turcica and interosternite 7/8 in trichodactylids underscore the monophyly of this family. The Dilocarcininae is characterized by having interosternites 5/6 through 7/8 restricted to the lateral sectors of the sternum, the lateral remnants of interosternite 4/5 forming prominent, rib-like ridges oriented diagonally to the longitudinal axis of the crab, and the median septum forming with interosternite 4/5 a Y-shaped pattern. These autapomorphies of the endophragmal system separate the trichodactylids from all other eubrachyurans and emphasize the morphological distinctness of the group. A description of the trichodactylid endophragmal junction plate is also provided.

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PubMed2002

On the roles of repetitive DNA elements in the context of a unified genomic-epigenetic system.

Repetitive DNA sequences comprise a substantial portion of most eukaryotic and some prokaryotic chromosomes. Despite nearly forty years of research, the functions of various sequence families as a whole and their monomer units remain largely unknown. The inability to map specific functional roles onto many repetitive DNA elements (REs), coupled with the taxon-specificity of sequence families, have led many to speculate that these genomic components are "selfish" replicators generating genomic "junk." The purpose of this paper is to critically examine the selfishness, evolutionary effects, and functionality of REs. First, a brief overview of the range of ideas pertaining to RE function is presented. Second, the argument is presented that the selfish DNA "hypothesis" is actually a narrative scheme, that it serves to protect neo-Darwinian assumptions from criticism, and that this story is untestable and therefore not a hypothesis. Third, attempts to synthesize the selfish DNA concept with complex systems models of the genome and RE functionality are critiqued. Fourth, the supposed connection between RE-induced mutations and macroevolutionary events are stated to be at variance with empirical evidence and theoretical considerations. Hypotheses that base phylogenetic transitions in repetitive sequence changes thus remain speculative. Fifth and finally, the case is made for viewing REs as integrally functional components of chromosomes, genomes, and cells. It is argued throughout that a new conceptual framework is needed for understanding the roles of repetitive DNA in genomic/epigenetic systems, and that neo-Darwinian "narratives" have been the primary obstacle to elucidating the effects of these enigmatic components of chromosomes.

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