BioEssays

Rudall, Paula J.

doi: 10.1002/bies.20488pmid: 17041880

Research on early‐divergent angiosperms, including Amborella, the putative sister to all other extant angiosperms, is increasingly used as a yardstick to infer the nature of the hypothetical ancestral angiosperm. Some traits are relatively diverse (and hence relatively labile) in this phylogenetic grade, compared with the more derived eudicot clade, in which developmental patterns have become increasingly canalized. One of the many mysteries surrounding the origin of the angiosperms is the evolutionary origin of the Polygonum‐type embryo sac (monosporic, eight‐nucleate and seven‐celled) that occurs in the majority of flowering plants. Observations on the megagametophyte of Amborella are conflicting, but a recent report of a supernumerary synergid in this genus raises the question of whether the Polygonum‐type embryo sac is derived by duplication of a four‐nucleate structure or by reduction from a multicellular structure. BioEssays 28: 1067–1071, 2006. © 2006 Wiley Periodicals, Inc.

Burke, Zoë D.; Tosh, David

doi: 10.1002/bies.20485pmid: 17041892

The liver contains two systems for the removal of ammonia—the urea cycle and the enzyme glutamine synthetase. These systems are expressed in a complementary fashion in two distinct populations of hepatocytes, referred to as periportal and perivenous cells. One of the unresolved problems in hepatology has been to elucidate the molecular mechanisms responsible for induction and maintenance of the cellular heterogeneity for ammonia detoxification. There is now a potential molecular explanation for the zonation of the urea cycle and glutamine synthetase based on the Wnt/β‐catenin pathway. BioEssays 28: 1072–1077, 2006. © 2006 Wiley Periodicals, Inc.

Wurdak, Heiko; Ittner, Lars M.; Sommer, Lukas

doi: 10.1002/bies.20484pmid: 17041894

DiGeorge syndrome is the most frequent microdeletion syndrome in humans, and is characterized by cardiovascular, thymic and parathyroid, and craniofacial anomalies. The underlying cause is disturbed formation of the pharyngeal apparatus, a transient structure present during vertebrate development that gives rise to endocrine glands, craniofacial tissue, and the cardiac outflow tract. The pharyngeal apparatus is composed of derivatives of ectoderm, endoderm, mesoderm and the neural crest. Thus, complex interactions between cell types from different origins have to be orchestrated in the correct spatiotemporal manner to establish proper formation of the pharyngeal system. The analysis of engineered mouse mutants developing a phenotype resembling DiGeorge syndrome has revealed genes and signalling pathways crucial for this process. Intriguingly, these mouse models reveal that interference with either of two distinct phases of pharyngeal apparatus development can contribute to the aetiology of DiGeorge syndrome. BioEssays 28: 1078–1086, 2006. © 2006 Wiley Periodicals, Inc.

Onami, Shuichi; Kitano, Hiroaki

doi: 10.1002/bies.20490pmid: 17041895

Genetic interactions provide information about genes and processes with overlapping functions in biological systems. For Saccharomyces cerevisiae, computational integration of multiple types of functional genomic data is used to generate genome‐wide predictions of genetic interactions. However, this methodology cannot be applied to the vastly more complex genome of metazoans, and only recently has the first metazoan genome‐wide prediction of genetic interactions been reported. The prediction for Caenorhabditis elegans was generated by computationally integrating functional genomic data from S. cerevisiae, C. elegans and Drosophila melanogaster. This achievement is an important step toward system‐level understanding of biological systems and human diseases. BioEssays 28: 1087–1090, 2006. © 2006 Wiley Periodicals, Inc.

Gechev, Tsanko S.; Van Breusegem, Frank; Stone, Julie M.; Denev, Iliya; Laloi, Christophe

doi: 10.1002/bies.20493pmid: 17041898

Reactive oxygen species (ROS) are known as toxic metabolic products in plants and other aerobic organisms. An elaborate and highly redundant plant ROS network, composed of antioxidant enzymes, antioxidants and ROS‐producing enzymes, is responsible for maintaining ROS levels under tight control. This allows ROS to serve as signaling molecules that coordinate an astonishing range of diverse plant processes. The specificity of the biological response to ROS depends on the chemical identity of ROS, intensity of the signal, sites of production, plant developmental stage, previous stresses encountered and interactions with other signaling molecules such as nitric oxide, lipid messengers and plant hormones. Although many components of the ROS signaling network have recently been identified, the challenge remains to understand how ROS‐derived signals are integrated to eventually regulate such biological processes as plant growth, development, stress adaptation and programmed cell death. BioEssays 28: 1091–1101, 2006. © 2006 Wiley Periodicals, Inc.

Jaeger, Johannes; Reinitz, John

doi: 10.1002/bies.20494pmid: 17041900

Morphogenetic fields are among the most fundamental concepts of embryology. However, they are also among the most ill‐defined, since they consist of dynamic regulatory processes whose exact nature remains elusive. In order to achieve a more rigorous definition of a developmental field, Lewis Wolpert introduced the concept of positional information illustrated by his French Flag model. Here we argue that Wolpert's positional information—a static coordinate system defining a field—lacks essential properties of the original field concept. We show how data‐driven mathematical modeling approaches now enable us to study regulatory processes in a way that is qualitatively different from our previous level of understanding. As an example, we review our recent analysis of segmentation gene expression in the blastoderm embryo of the fruit fly Drosophila melanogaster. Based on this analysis, we propose a revised French Flag, which incorporates the dynamic, feedback‐driven nature of pattern formation in the Drosophila blastoderm. BioEssays 28: 1102–1111, 2006. © 2006 Wiley Periodicals, Inc.

Salazar‐Ciudad, Isaac

doi: 10.1002/bies.20482pmid: 17041901

It has been repeatedly claimed that morphological novelties are an unresolved problem in evolutionary theory. Several definitions of novelty exist but most emphasize that novelties imply qualitative changes on the phenotype and not the quantitative gradual changes favored in the neo‐Darwinian approach to evolutionary theory. This article discusses how the concept of novelty is used to describe aspects of morphological evolution that are not satisfactorily explained under the modern synthesis. In this article, it is suggested that there is a repertoire of morphological changes rather than two discrete qualitatively different types of morphological change. How these different types of morphological changes can be understood from the diversity of developmental mechanisms existing in animal development is explored. Specifically, it is proposed that animal morphology and its variation can be understood from the spatial patterns produced by a set of basic developmental mechanisms and their combination. Some specific examples of these kinds of morphologic changes are explained. BioEssays 28: 1112–1122, 2006. © 2006 Wiley Periodicals, Inc.

Holliday, Robin

doi: 10.1002/bies.20492pmid: 17041902

The earliest eukaryote species almost certainly evolved in an environment dominated by numerous prokaryotic species. If the first eukaryotic cells were larger and grew more slowly than their prokaryotic neighbours, they might well have been at a competitive disadvantage. It is proposed here that the early evolution of meiosis, with its capacity for generating new favourable gene combinations, might have served to offset any such competitive disadvantages. Meiosis and sex could have arisen in an asexually reproducing species and formed a clonal population. BioEssays 28: 1123–1125, 2006. © 2006 Wiley Periodicals, Inc.

Takács‐Vellai, Krisztina; Bayci, Andrew; Vellai, Tibor

doi: 10.1002/bies.20489pmid: 17041904

The regulation of ageing has been extensively studied in divergent animal model systems including worms, flies and mice. However, little is known about the cellular pathways that mediate the death of these organisms. Analysing major cellular changes in the ageing nematode Caenorhabditis elegans has revealed a gradual, progressive deterioration of different tissues except for the nervous system, which remarkably preserves its integrity even in advanced old age. In addition, genetic data have shown that, in C. elegans and in the fruit fly Drosophila melanogaster, lifespan is controlled by signals derived from neurons and acting throughout adulthood. Organismal death thus seems to be a consequence of the decline of specific neurons. Accumulating evidence demonstrates that late onset of neuronal cell loss generally occurs via autophagy, a process in which eukaryotic cells self‐digest parts of their contents during development or to survive starvation. Here we suggest that overactivation of autophagy in the cells of the nervous system is the eventual cause of “physiological” death. BioEssays 28: 1126–1131, 2006. © 2006 Wiley Periodicals, Inc.

Denman, Robert B.

doi: 10.1002/bies.20491pmid: 17041905

The interaction of RNA‐binding proteins (RBPs) with RNA is a crucial aspect of normal cellular metabolism. Yet, the diverse number of RBPs and RNA motifs to which they bind, the wide range of interaction strengths and the fact that RBPs associate in dynamic complexes have made it challenging to determine whether a particular RNA‐binding protein binds a particular RNA. Recent work by three different laboratories has led to the development of new tools to query such interactions in the more physiological environs of cultured cells. The use of these methods has led to insights into (1) the networks of RNAs regulated by a particular protein, (2) the identification of new protein partners within messenger ribonucleoprotein particles and (3) the flux of RNA‐binding proteins on an mRNA throughout its lifecycle. Here, I examine these new methods and discuss their relative strengths and current limitations. BioEssays 28: 1132–1143, 2006. © 2006 Wiley Periodicals, Inc.