DAF-12 regulates a connected network of genes to ensure robust developmental decisions

The nuclear receptor DAF-12 has roles in normal development, the decision to pursue dauer development in unfavorable conditions, and the modulation of adult aging. Despite the biologic importance of DAF-12, target genes for this receptor are largely unknown. To identify DAF-12 targets, we performed chromatin immunoprecipitation followed by hybridization to whole-genome tiling arrays. We identified 1,175 genomic regions to be bound in vivo by DAF-12, and these regions are enriched in known DAF-12 binding motifs and act as DAF-12 response elements in transfected cells and in transgenic worms. The DAF-12 target genes near these binding sites include an extensive network of interconnected heterochronic and microRNA genes. We also identify the genes encoding components of the miRISC, which is required for the control of target genes by microRNA, as a target of DAF-12 regulation. During reproductive development, many of these target genes are misregulated in daf-12(0) mutants, but this only infrequently results in developmental phenotypes. In contrast, we and others have found that null daf-12 mutations enhance the phenotypes of many miRISC and heterochronic target genes. We also find that environmental fluctuations significantly strengthen the weak heterochronic phenotypes of null daf-12 alleles. During diapause, DAF-12 represses the expression of many heterochronic and miRISC target genes, and prior work has demonstrated that dauer formation can suppress the heterochronic phenotypes of many of these target genes in post-dauer development. Together these data are consistent with daf-12 acting to ensure developmental robustness by committing the animal to adult or dauer developmental programs despite variable internal or external conditions.     

Behavioral choices: how neuronal networks make decisions

To survive, animals must constantly make behavioral choices. The analysis of simple, almost binary, behavioral choices in invertebrate animals with restricted nervous systems is beginning to yield insight into how neuronal networks make such decisions.     

Molecules that make axons grow

The study of neurite growth in tissue culture has been a productive way to identify substances that may control the behavior of axons in vivo. Molecules that promote the outgrowth of neurites include nerve growth factor, laminin, fibronectin, and a protease inhibitor derived from glia. Evidence that these molecules may influence axon growth and guidance in vivo is discussed. The effects these molecules have at the cellular level are compared, in an attempt to identify common mechanisms of action. Several less well-characterized molecules that influence the behavior of neurites are also discussed.     

Specialists make faster decisions than generalists: experiments with aphids

Theoretical studies and a few recent experimental reports suggest that the evolution of diet breadth in herbivorous insects is constrained by a limited neural ability to efficiently process large amounts of information in short periods of time. This neural-constraints hypothesis predicts that generalist herbivores should make slower or poorer decisions than specialists when selecting plants, because generalists must discriminate and decide among stimuli from a wider variety of potential hosts. The present study compares the speed with which host-associated decisions are made in specialist versus generalist populations of the aphid Uroleucon ambrosiae. Populations of U. ambrosiae from eastern North America are highly specific to the host plant Ambrosia trifida (Asteraceae), whereas those from the American southwest also feed on a variety of other taxa from the Asteraceae. Experiments with winged (alate) and wingless (apterous) individuals showed that host-finding, host-selection, host-acceptance, host-sampling and host-settling were more efficiently performed by the eastern specialists. These very consistent results provide evidence that strongly supports the neural-constraints hypothesis.     

T-Box Genes and Developmental Decisions That Cells Make

Russian Journal of Developmental Biology -     

Horseshoe bats make adaptive prey-selection decisions, informed by echo cues

Foragers base their prey-selection decisions on the information acquired by the sensory systems. In bats that use echolocation to find prey in darkness, it is not clear whether the specialized diet, as sometimes found by faecal analysis, is a result of active decision-making or rather of biased sensory information. Here, we tested whether greater horseshoe bats decide economically when to attack a particular prey item and when not. This species is known to recognize different insects based on their wing-beat pattern imprinted in the echoes. We built a simulation of the natural foraging process in the laboratory, where the bats scanned for prey from a perch and, upon reaching the decision to attack, intercepted the prey in flight. To fully control echo information available to the bats and assure its unambiguity, we implemented computer-controlled propellers that produced echoes resembling those from natural insects of differing profitability. The bats monitored prey arrivals to sample the supply of prey categories in the environment and to inform foraging decisions. The bats adjusted selectivity for the more profitable prey to its inter-arrival intervals as predicted by foraging theory (an economic strategy known to benefit fitness). Moreover, unlike in previously studied vertebrates, foraging performance of horseshoe bats was not limited by costly rejections of the profitable prey. This calls for further research into the evolutionary selection pressures that sharpened the species's decision-making capacity.     

FLD interacts with genes that affect different developmental phase transitions to regulate Arabidopsis shoot development

A new fld mutant allele, fld-2, which significantly delayed flowering, was isolated and characterized in Arabidopsis thaliana. Even under long-day conditions after more than 100 days in the greenhouse, the majority of fld-2 mutant plants had not bolted. In addition, mutant inflorescences produced more than 10 co-florescences that were subtended by a high number of rosette-like leaves before giving rise to flowers. The late-flowering phenotype of the fld-2 mutation could be partially overcome by both vernalization and GA treatment but it was not influenced by 5-azaC treatment. Phenotypic analyses of double mutants indicated that fld-2 is epistatic to early flowering mutants elf1, elf2 and elf3. In addition, fld-2 could enhance vegetative characteristics in embryonic flower 1 (emf1) mutants by causing many small sessile leaves in fld-2 emf1 double mutants. The relief of the terminal flower 1 (tfl1) mutant phenotype in fld-2 tfl1 double mutants, and the enhancement of leafy (lfy) and apetala1 (ap1) mutant phenotypes in fld-2 lfy and fld-2 ap1 double mutants, suggest that FLD is also likely to be involved in the floral transition. Our results strongly suggest that the FLD gene plays a key role in regulating the reproductive competence of the shoot and results in different developmental phase transitions in Arabidopsis.     

Competence to make decisions: the psychology of deliberate decision making

This paper examines the psychological structure of mental competence, conceived of as competence in deliberate decision making. Analysis of that structure may be useful in understanding mental incompetence, as it occurs among some elderly persons. Mental competence not only depends on a number of cognitive abilities, such as foreseeing consequences, but also on the intactness of emotions, insight in one's own emotions, and abilities for emotion regulation.