BioEssays

Renfree, Marilyn B.

doi: 10.1002/bies.20670pmid: 17935149

Australia is thought of as the home of marsupials, but South America has 60 or so species of these interesting mammals. The genome of one of these, the South American grey short‐tailed opossum, Monodelphis domestica, has just been sequenced and published in June.1 The high quality 6× coverage is the first marsupial genome completed, pipping the 2× coverage of the Australian tammar wallaby at the post by half a year. The opossum genome has an unusual structure with fewer chromosomes than the human genome (9 pairs versus 23 pairs) but a longer total length (3.4 billion versus 3 billion bases). The opossum autosomes, like those of all marsupials, are extremely large but, in contrast, the X chromosome is only 76 Mb long. The opossum genome has turned up several surprises and provided critical new information on the evolution of mammalian genomes2–6. BioEssays 29:1073–1076, 2007. © 2007 Wiley Periodicals, Inc.

Ponjavic, Jasmina; Ponting, Chris P.

doi: 10.1002/bies.20669pmid: 17935150

The landscapes of mammalian genomes are characterized by complex patterns of intersecting and overlapping sense and antisense transcription, giving rise to large numbers of coding and non‐protein‐coding RNAs (ncRNAs). A recent report by Kapranov and colleagues1 describes three potentially novel classes of RNAs located at the very edges of protein‐coding genes. The presence of RNAs from one of these classes appears to be correlated with the expression levels of their associated genes. These results suggest that a proportion of these RNAs might have roles in the cis‐regulation of neighbouring protein‐coding genes' expression. BioEssays 29:1077–1080, 2007. © 2007 Wiley Periodicals, Inc.

Hughes, Nigel C.

doi: 10.1002/bies.20674pmid: 17935151

Analysis of the degree of intraspecific morphological polymorphism during the evolutionary history of trilobites using an informatic approach1 provides striking evidence of a long‐suspected but previously unsubstantiated pattern: degrees of polymorphism are markedly higher in phylogenetically basal, stratigraphically early species. This unequivocal pattern prompts further exploration of the relationship between microevolutionary variance and macroevolutionary history. It demonstrates that the ‘traditional’ fossil record of skeletonized organisms can provide unique insight into questions of major evolutionary interest. BioEssays 29:1081–1084, 2007. © 2007 Wiley Periodicals, Inc.

Breitling, Rainer

doi: 10.1002/bies.20663pmid: 17935218

The close link between signaling by the developmental regulators of the Hedgehog family and cholesterol biochemistry has been known for some time. The morphogen is covalently attached to cholesterol in a peculiar autocatalytic reaction and embryonal disruption of cholesterol synthesis leads to malformations that mimic Hh signaling defects. Recently, it was furthermore shown that secreted Hh could hitchhike on lipoprotein particles to establish its morphogenic gradient in the developing embryo. Additionally, there is new evidence that the Hh‐receptor Patched transmits the Hh signal by modulating the secretion of an inhibitory sterol molecule from the receiving cells. Here we present some of the most recent discoveries on the Hh–sterol link and discuss their implications from a systems design perspective. We predict that a robust functioning of the Hh pathway will require the involvement of more sterol metabolites, and these should be the subject of future research. BioEssays 29:1085–1094, 2007. © 2007 Wiley Periodicals, Inc.

Meier, Sebastian; Özbek, Suat

doi: 10.1002/bies.20661pmid: 17935152

While Darwin pictured organismal evolution as “descent with modification” more than 150 years ago, a detailed reconstruction of the basic evolutionary transitions at the molecular level is only emerging now. In particular, the evolution of today's protein structures and their concurrent functions has remained largely mysterious, as the destruction of these structures by mutation seems far easier than their construction. While the accumulation of genomic and structural data has indicated that proteins are related via common ancestors, naturally occurring protein structures are often considered to be evolutionarily robust, thus leaving open the question of how protein structures can be remodelled while selective pressure forces them to function. New information on the proteome, however, increasingly explains the nature of local and global conformational diversity in protein evolution, which allows the acquisition of novel functions via molecular transition forms containing ancestral and novel structures in dynamic equilibrium. Such structural plasticity may permit the evolution of new protein folds and help account for both the origins of new biological functions and the nature of molecular defects. BioEssays 29:1095–1104, 2007. © 2007 Wiley Periodicals, Inc.

Schrader, Michael; Yoon, Yisang

doi: 10.1002/bies.20659pmid: 17935214

Mitochondria and peroxisomes are essential subcellular organelles in mammals. Despite obvious differences, both organelles display certain morphological and functional similarities. Recent studies have elucidated that these highly dynamic and plastic organelles share components of their division machinery. Mitochondria and peroxisomes are metabolically linked organelles, which are cooperating and cross‐talking. This review addresses the dynamics and division of mitochondria and peroxisomes as well as their functional similarities to provide insight as to why these organelles share the fission machinery in evolutionary aspects.© 2007 Wiley Periodicals, Inc.

Hardtke, Christian S.

doi: 10.1002/bies.20653pmid: 17935219

The plant hormones auxin and brassinosteroid are both essential regulators of plant growth and known to influence both cell division and cell elongation in various developmental contexts. These physiological effects of auxin and brassinosteroid have been known for many years. Based on observations from external simultaneous application of both hormones to plant tissues, it has been suggested that they act in an interdependent and possibly synergistic manner. Recent work in the model plant Arabidopsis thaliana suggests that, at the molecular level, auxin–brassinosteroid synergism manifests itself in the regulation of the expression of common target genes. However, whether this reflects genuine hormone pathway‐dependent crosstalk modulation of the transcription machinery or rather indirect effects of hormone action on other cellular activities, such as hormone biosynthesis or the polar transport of auxin, is not entirely clear. This article reviews the evidence for transcriptional crosstalk between auxin and brassinosteroid and its molecular basis. BioEssays 29:1115–1123, 2007. © 2007 Wiley Periodicals, Inc.

Singh, Mohan B.; Bhalla, Prem L.

doi: 10.1002/bies.20660pmid: 17935220

Plant reproduction is vital for species survival, and is also central to the production of food for human consumption. Seeds result from the successful fertilization of male and female gametes, but our understanding of the development, differentiation of gamete lineages and fertilization processes in higher plants is limited. Germ cells in animals diverge from somatic cells early in embryo development, whereas plants have distinct vegetative and reproductive phases in which gametes are formed from somatic cells after the plant has made the transition to flowering and the formation of the reproductive organs. Recently, novel insights into the molecular mechanisms underlying male germ‐line initiation and male gamete development in plants have been obtained. Transcriptional repression of male germ‐line genes in non‐male germ‐line cells have been identified as a key mechanism for spatial and temporal control of male germ‐line development. This review focuses on molecular events controlling male germ‐line development especially, on the nature and regulation of gene expression programs operating in male gametes of flowering plants. BioEssays 29:1124–1132, 2007. © 2007 Wiley Periodicals, Inc.

Stewart, Scott; Rojas‐Muñoz, Agustin; Belmonte, Juan Carlos Izpisúa

doi: 10.1002/bies.20656pmid: 17935197

All cells have electric potentials across their membranes, but is there really compelling evidence to think that such potentials are used as instructional cues in developmental biology? Numerous reports indicate that, in fact, steady, weak bioelectric fields are observed throughout biology and function during diverse biological processes, including development. Bioelectric fields, generated upon amputation, are also likely to play a key role during vertebrate regeneration by providing the instructive cues needed to direct migrating cells to form a wound epithelium, a structure unique to regenerating animals. However, mechanistic insight is still sorely lacking in the field. What are the genes required for bioelectric‐dependent cell migration during regeneration? The power of genetics combined with the use of zebrafish offers the best opportunity for unbiased identification of the molecular players in bioelectricity. BioEssays 29:1133–1137, 2007. © 2007 Wiley Periodicals, Inc.

Hauton, Chris; Smith, Valerie J.

doi: 10.1002/bies.20650pmid: 17935208

Recently claims have been made for radical new insights in the field of invertebrate immunology that involve memory, specificity and/or maternal transfer of immunocompetence. For evidence these claims rely on phenomena, such as survival or reproductive capacity, observed at the level of the whole organism. The allure of these apparently revelatory hypotheses is that they are contrary to established views of innate immunity. They draw implicit analogy to adaptive responses in jawed vertebrates and the terminology used creates an incomplete and misleading picture. We argue that the case for adaptive immunity in invertebrates based only on such phenomena is weak and flawed, as it can only be upheld if supported by descriptions of the underlying mechanisms. We caution against a reliance on this approach as a means of advancing this field—highlighting, as an example, some negative commercial implications of adopting this approach. BioEssays 29:1138–1146, 2007. © 2007 Wiley Periodicals, Inc.