The NAADP receptor: new receptors or new regulation?

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent calcium mobilizing messenger yet discovered. Its action has now been reported in a large number of cell types from a diverse array of organisms, and in some cases linked to the transduction of specific cellular stimuli. However, what is controversial is the nature of its target calcium release channel, as well as the subcellular localization of its receptor. Some have proposed that NAADP activates a novel calcium release channel distinct from the two major classes of channels known, the inositol trisphosphate receptors and ryanodine receptors. However, others have suggested that it acts in a novel way to regulate a known calcium release channel, the ryanodine receptor.     

Melatonin and corticosterone regulation: Feeding time or the light:Dark cycle?

Under ad libitum feeding, male rats exhibit a marked rhythm of plasma and pineal melatonin; levels are low during the day and high at night. Restricting food availability to a 2 hour period during the light or dark does not markedly influence the melatonin rhythm, both groups having a crest in circulating melatonin during the dark. In contrast, plasma corticosterone levels are influenced by both the light-dark cycle and feeding. Animals fed early in the light period exhibit a biomodal corticosterone secretory pattern, with high steroid levels immediately prior to feeding and again just before lights-out, animals fed early in the dark have a single crest, just before food presentation. These data provide evidence for the dissociation of melatonin and corticosterone secretory patterns, providing support for the hypothesis that multiple regulators control neuroendocrine rhythmicity.     

Cell cycle: who turns the crank?

The oscillating activity of a single CDK-cyclin fusion protein can drive the orderly progression of yeast cells through DNA replication, mitosis and cell division.     

Cell cycle: the key to plant growth control?

Experimental evidence on the role of the cell cycle in plant growth regulation does not exclusively fit the cellular (division drives growth) or the organismal perspective (division merely accompanies growth). Here we present a broader, integrated concept of plant growth regulatory interactions, which accommodates experimental results gathered to date. This model can serve as a basis for future research, and prompts experimental approaches to encompass both measurements of cell growth and division parameters.     

Social behavior and comparative genomics: new genes or new gene regulation?

Molecular analyses of social behavior are distinguished by the use of an unusually broad array of animal models. This is advantageous for a number of reasons, including the opportunity for comparative genomic analyses that address fundamental issues in the molecular biology of social behavior. One issue relates to the kinds of changes in genome structure and function that occur to give rise to social behavior. This paper considers one aspect of this issue, whether social evolution involves new genes, new gene regulation, or both. This is accomplished by briefly reviewing findings from studies of the fish Haplochromis burtoni , the vole Microtus ochrogaster , and the honey bee Apis mellifera , with a more detailed and prospective consideration of the honey bee.     

Universal cell cycle regulation?

The mechanisms that couple the control of initiation of chromosome replication and cell division to the mass increase of a growing cell are not understood. Here, models are considered in which replication and division are controlled through signals generated by completion of different morphological steps during cell cycle progression.     

Cell growth: downstream of Myc - to grow or to cycle?

For many years, Myc function has been linked to the control of cell-cycle progression. Now, increasing evidence shows that Myc also controls cell growth, and that these two processes are regulated independently.     

Genome sequencing in the sea urchin embryo: what is new concerning the cell cycle?

Sea urchin is a classical research model system in developmental biology; moreover, the external fertilization and growth of embryos, their rapid division cycle, their transparency and the accessibility of these embryos to molecular visualization methods, made them good specimens to analyze the regulatory mechanisms of cell division. These features as well as the phylogenetic position of sea urchin, close to vertebrates but in an outgroup within the deuterostomes, led scientists working on this model to sequence the genome of the species S. purpuratus. The genome contains a full repertoire of cell cycle control genes. A comparison of this toolkit with those from vertebrates, nematodes, drosophila, as well as tunicates, provides new insight into the evolution of cell cycle control. While some gene subtypes have undergone lineage-specific expansions in vertebrates (i.e. cyclins, mitotic kinases,...), others seem to be lost in vertebrates, for instance the novel cyclin B identified in S. purpuratus. On the other hand, some genes which were previously thought to be vertebrate innovations, are also found in sea urchins (i.e. MCM9). To note is also the absence of cell cycle inhibitors of the INK type, which are apparently confined to vertebrates. The uncovered genomic repertoire of cell-cycle regulators will thus provide molecular tools that should further enhance future research on cell cycle control and developmental regulation in this model.     

Pluralism or unity in biology: could microbes hold the secret to life?

Pluralism is popular among philosophers of biology. This essay argues that negative judgments about universal biology, while understandable, are very premature. Familiar life on Earth represents a single example of life and, most importantly, there are empirical as well as theoretical reasons for suspecting that it may be unrepresentative. Scientifically compelling generalizations about the unity of life (or lack thereof) must await the discovery of forms of life descended from an alternative origin, the most promising candidate being the discovery of extraterrestrial life. Nonetheless, in the absence of additional examples of life, we are best off exploring the microbial world for promising explanatory concepts, principles, and mechanisms rather than prematurely giving up on universal biology. Unicellular microbes (especially prokaryotes) are by far the oldest, metabolically most diverse, and environmentally tolerant form of life on our planet. Yet somewhat ironically, much of our theorizing about life still implicitly privileges complex multicellular eukaryotes, which are now understood to be highly specialized, fragile latecomers to Earth. The problem with pursuing a pluralist approach to understanding life is that it is likely to blind us to the significance of just those entities and causal processes most likely to shed light on the underlying nature of life.     

Vascular cell biology in vivo: a new piscine paradigm?

Understanding how blood vessels form has become increasingly important in recent years yet remains difficult to study. The architecture and context of blood vessels are difficult to reproduce in vitro, and most developing blood vessels in vivo are relatively inaccessible to observation and experimental manipulation. Zebrafish, however, provide several advantages. They have small, accessible, transparent embryos and larvae, facilitating high-resolution imaging in vivo. In addition, genetic and experimental tools and methods are available for functional manipulation of the entire organism, vascular tissues or even single vascular- or non-vascular cells. Together, these features make the fish amenable to 'in vivo vascular cell biology'.