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Modular Nature (modular + nature)

Distribution by Scientific Domains

Life Sciences	40%
Chemistry	40%

Selected Abstracts

THE LOCUS OF EVOLUTION: EVO DEVO AND THE GENETICS OF ADAPTATION

EVOLUTION, Issue 5 2007
Hopi E. Hoekstra
An important tenet of evolutionary developmental biology ("evo devo") is that adaptive mutations affecting morphology are more likely to occur in the cis -regulatory regions than in the protein-coding regions of genes. This argument rests on two claims: (1) the modular nature of cis -regulatory elements largely frees them from deleterious pleiotropic effects, and (2) a growing body of empirical evidence appears to support the predominant role of gene regulatory change in adaptation, especially morphological adaptation. Here we discuss and critique these assertions. We first show that there is no theoretical or empirical basis for the evo devo contention that adaptations involving morphology evolve by genetic mechanisms different from those involving physiology and other traits. In addition, some forms of protein evolution can avoid the negative consequences of pleiotropy, most notably via gene duplication. In light of evo devo claims, we then examine the substantial data on the genetic basis of adaptation from both genome-wide surveys and single-locus studies. Genomic studies lend little support to the cis -regulatory theory: many of these have detected adaptation in protein-coding regions, including transcription factors, whereas few have examined regulatory regions. Turning to single-locus studies, we note that the most widely cited examples of adaptive cis -regulatory mutations focus on trait loss rather than gain, and none have yet pinpointed an evolved regulatory site. In contrast, there are many studies that have both identified structural mutations and functionally verified their contribution to adaptation and speciation. Neither the theoretical arguments nor the data from nature, then, support the claim for a predominance of cis -regulatory mutations in evolution. Although this claim may be true, it is at best premature. Adaptation and speciation probably proceed through a combination of cis -regulatory and structural mutations, with a substantial contribution of the latter. [source]

Modular Furanoside Phosphite-Phosphoroamidites, a Readily Available Ligand Library for Asymmetric Palladium-Catalyzed Allylic Substitution Reactions.

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009
Origin of Enantioselectivity
Abstract A library of furanoside phosphite-phosphoroamidite ligands has been synthesized and screened in the palladium-catalyzed allylic substitution reactions of several substrate types. These series of ligands can be prepared efficiently from easily accessible D -xylose and D -glucose. Their modular nature enables the position of the phosphoroamidite group, configuration of C-3 of the furanoside backbone and the substituents/configurations in the biaryl phosphite/phosphoroamidite moieties to be easily and systematically varied. By carefully selecting the ligand components, therefore, high regio- and enantioselectivities (ees up to 98%) and good activities have been achieved in a broad range of mono- and disubstituted hindered and unhindered linear and cyclic substrates. The NMR studies on the palladium-,-allyl intermediates provide a deeper understanding about the effect of the ligand parameters on the origin of enantioselectivity. They also indicate that the nucleophilic attack takes place predominantly at the allylic terminal carbon atom located trans to the phosphoroamidite moiety. [source]

Charles Darwin, embryology, evolution and skeletal plasticity

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2010
B. K. Hall
Summary Darwin provided us with the theory of evolutionary change through natural selection. Just as important to the science of biology was Darwin's recognition that all organisms could be classified and were related to one another because they arose from a single common universal ancestor , what we know as the universal tree of life (UtoL). All the features of the skeletal biology of fish therefore can be explained, both in an evolutionary framework (ultimate causation) and in the framework of development, growth and physiology (proximate causation). Neither approach is complete without the other. I will outline the elements of Darwin's theories on evolution and classification and, as importantly, discuss what was missing from Darwin's theories. An important class of evidence for evolution used by Darwin came from embryology, both comparative embryology and the existence of vestiges and atavisms. After discussing this evidence I examine some fundamental features of skeletal development and evolution These include: the presence of four skeletal systems in all vertebrates; the existence of two skeletons, one based on cartilage, the other on bone and dentine; the modular nature of skeletal development and evolution; and the plasticity of the skeleton in response to either genetic or environmental changes. [source]

Carbohydrate translocation determines the phenolic content of Populus foliage: a test of the sink,source model of plant defense

NEW PHYTOLOGIST, Issue 1 2004
Tom Arnold
Summary ,,Here, we examine the influence of source-to-sink carbohydrate (CHO) flow on the development of constitutive and inducible levels of phenylpropenoids in hybrid poplar (Populus nigra × P. deltoides) foliage to determine if secondary metabolic processes in plant modules can be inhibited in a predictable manner by events such as herbivory and the development of new leaves and reproductive structures, which alter the path of phloem-borne resources. ,,Phenylpropenoid concentrations were determined for developing foliage after CHO flow, measured as the translocation of 13C from labeled sources was manipulated. ,,Phenylpropenoid metabolism in both unwounded and induced sink leaves was directly and positively linked to rates of CHO import. Alterations in rates of translocation yielded different results, depending on how CHO import was affected: the removal of competing sinks rapidly and dramatically increased leaf phenolic contents, whereas phenolic levels (and their inducibility) tended to be reduced when import was interrupted. ,,High and inducible sink strength in developing poplar leaves provides resources for phenolic biosynthesis and, as a result, restrictions or re-directions of CHOs affect the foliar quality. Sink strength and the vascular architecture of plants, which confer upon them a modular nature, can determine the direction and magnitude of defense responses in trees. [source]

Ru-catalyzed Asymmetric Hydrogenation of Aryl Ketones Using Tetrazole Derived NH2 -hybrid Ligand

CHINESE JOURNAL OF CHEMISTRY, Issue 12 2009
Fusheng Bie
Abstract Readily available chiral hybrid NH2/tetrazole ligand [(S)-TEA, 1] in combination with Ru-BINAP or Ru-DIOP complexes catalyzes the asymmetric hydrogenation of a number of simple ketones with moderate enantioselectivity (up to 72% ee). The tetrazole functionality results in reversal of the typically observed chiral-induction for related systems and allows for hydrogenation to be uncharacteristically conducted in (non-protic) THF solvent. The observed catalyst performance is sensitive to the reaction conditions employed and the particular compounds involved. The origins of such features are considered to derive from the added functionality provided by the tetrazole moiety in 1, which due to its modular nature provides a good basis for further development. [source]