Dioecious Silene at the X-road: the reasons Y

Among the variety of breeding systems developed by flowering plants, those based on heteromorphic sex chromosomes are the most intellectually challenging in evolutionary terms. This is because, among other things, they enable us to compare sex determination processes between plants and animals. White campion (Silene latifolia, also named Lychnis or Melandrium) is dioecious and, much like us, females are homogametic (XX) and males are heterogametic (XY). Sexual dimorphism in white campion is controlled by two independent developmental pathways operating from the Y chromosome at very early developmental stages and within distinct regions of the flower. In addition, all basic steps in the evolution from the bisexual to the dioecious condition with heteromorphic sex chromosomes are known and available to experimentation in the genus Silene. This group of species has been under scrutiny for more than a century. Such an ideal experimental system enables us to tackle, with novel methodological tools, several classical questions in biology. These include the question of how sexual dimorphism evolved and how dimorphic development is controlled, as well as questions of how sex chromosomes evolve in the absence of meiotic recombination or how male-female genetic conflicts are generated. At the turn of the century, the time is now ripe to have a closer look. Received: 21 September 1999 / Accepted: 11 October 1999     

Activation of hypothalamic RIP‐Cre neurons promotes beiging of WAT via sympathetic nervous system

Activation of brown adipose tissue (BAT) and beige fat by cold increases energy expenditure. Although their activation is known to be differentially regulated in part by hypothalamus, the underlying neural pathways and populations remain poorly characterized. Here, we show that activation of rat‐insulin‐promoter‐Cre (RIP‐Cre) neurons in ventromedial hypothalamus (VMH) preferentially promotes recruitment of beige fat via a selective control of sympathetic nervous system (SNS) outflow to subcutaneous white adipose tissue (sWAT), but has no effect on BAT. Genetic ablation of APPL2 in RIP‐Cre neurons diminishes beiging in sWAT without affecting BAT, leading to cold intolerance and obesity in mice. Such defects are reversed by activation of RIP‐Cre neurons, inactivation of VMH AMPK, or treatment with a β3‐adrenergic receptor agonist. Hypothalamic APPL2 enhances neuronal activation in VMH RIP‐Cre neurons and raphe pallidus, thereby eliciting SNS outflow to sWAT and subsequent beiging. These data suggest that beige fat can be selectively activated by VMH RIP‐Cre neurons, in which the APPL2–AMPK signaling axis is crucial for this defending mechanism to cold and obesity.     

Independent origin of sex chromosomes in two species of the genus Silene

Here we introduce a new model species, Silene colpophylla, that could facilitate research of sex chromosome evolution and sex-determining systems. This species is related to the well-established dioecious plant model Silene latifolia. Our results show that S. colpophylla is, similarly to S. latifolia, a male heterogametic species, but its sex chromosomes have evolved from a different pair of autosomes than in S. latifolia. The results of our phylogenetic study and mapping of homologs of S. latifolia X-linked genes indicate that the sex determination system in S. colpophylla evolved independently from that in S. latifolia. We assert that this model species pair will make it possible to study two independent patterns of sex chromosome evolution in related species.     

Systems biology towards life in silico: mathematics of the control of living cells

Systems Biology is the science that aims to understand how biological function absent from macromolecules in isolation, arises when they are components of their system. Dedicated to the memory of Reinhart Heinrich, this paper discusses the origin and evolution of the new part of systems biology that relates to metabolic and signal-transduction pathways and extends mathematical biology so as to address postgenomic experimental reality. Various approaches to modeling the dynamics generated by metabolic and signal-transduction pathways are compared. The silicon cell approach aims to describe the intracellular network of interest precisely, by numerically integrating the precise rate equations that characterize the ways macromolecules’ interact with each other. The non-equilibrium thermodynamic or ‘lin–log’ approach approximates the enzyme rate equations in terms of linear functions of the logarithms of the concentrations. Biochemical Systems Analysis approximates in terms of power laws. Importantly all these approaches link system behavior to molecular interaction properties. The latter two do this less precisely but enable analytical solutions. By limiting the questions asked, to optimal flux patterns, or to control of fluxes and concentrations around the (patho)physiological state, Flux Balance Analysis and Metabolic/Hierarchical Control Analysis again enable analytical solutions. Both the silicon cell approach and Metabolic/Hierarchical Control Analysis are able to highlight where and how system function derives from molecular interactions. The latter approach has also discovered a set of fundamental principles underlying the control of biological systems. The new law that relates concentration control to control by time is illustrated for an important signal transduction pathway, i.e. nuclear hormone receptor signaling such as relevant to bone formation. It is envisaged that there is much more Mathematical Biology to be discovered in the area between molecules and Life.     

Proteomic analysis during larval development and metamorphosis of the spionid polychaete Pseudopolydora vexillosa

Background  

While the larval-juvenile transition (metamorphosis) in the spionid polychaete Pseudopolydora vexillosa involves gradual morphological changes and does not require substantial development of juvenile organs, the opposite occurs in the barnacle Balanus amphitrite. We hypothesized that the proteome changes during metamorphosis in the spionids are less drastic than that in the barnacles. To test this, proteomes of pre-competent larvae, competent larvae (ready to metamorphose), and juveniles of P. vexillosa were compared using 2-dimensional gel electrophoresis (2-DE), and they were then compared to those of the barnacle.     

Transgenic analysis of the physiological functions of Mahogunin ring finger‐1 isoforms

Mahogunin Ring Finger‐1 (Mgrn1) null mutant mice have a pleiotropic phenotype that includes the absence of yellow hair pigment, abnormal head shape, reduced viability, and adult‐onset spongiform neurodegeneration. Mgrn1 encodes a highly conserved E3 ubiquitin ligase with four different isoforms which are differentially expressed and predicted to localize to different subcellular compartments. To test whether loss of specific isoforms causes different aspects of the mutant phenotype, we generated transgenes for each isoform and bred them onto the null mutant background. Mice expressing only isoform I or III appeared completely normal. Isoform II rescued or partially rescued the mutant phenotypes, whereas isoform IV had little or no effect. Our data show that different Mgrn1 isoforms are not functionally equivalent in vivo and that the presence of only isoform I or III is sufficient for normal development, pigmentation, and neuronal integrity. genesis 47:524–534, 2009. © 2009 Wiley‐Liss, Inc.