Dynamic de novo adipose tissue development during metamorphosis in Drosophila melanogaster.

Adipose tissue is a central organ for controlling systemic metabolism both in invertebrates and vertebrates. Here, we have investigated the developmental processes of the adult-type fat body (AFB) in Drosophila. We have established genetic tools that allow visualization and genetic manipulations of cells in the AFB lineage from early in metamorphosis. We identified precursor cells that give rise to the AFB and delineated dynamic cellular behaviors underlying AFB formation. These precursor cells displayed polarized cell shapes and oriented motility, with emigration from the thorax and subsequent dispersal to the abdomen and head. After the migration period, these cells adhered to each other, assembling into the AFB with a sheet-like architecture. Continuous cell proliferation occurred during and after the large-scale migration to achieve appropriate fat tissue mass. Homotypic cell fusion after the sheet formation contributed to the establishment of multinucleated cells in the AFB. We also examined candidate gene functions, and our results argue that ecdysone signaling and the transcription factor Serpent support adult fat body organogenesis.

The seven-pass transmembrane cadherin Flamingo controls dendritic self-avoidance via its binding to a LIM domain protein, Espinas, in Drosophila sensory neurons.

Members of the Flamingo cadherin family are required in a number of different in vivo contexts of neural development. Even so, molecular identities downstream from the family have been poorly understood. Here we show that a LIM domain protein, Espinas (Esn), binds to an intracellular juxtamembrane domain of Flamingo (Fmi), and that this Fmi-Esn interplay elicits repulsion between dendritic branches of Drosophila sensory neurons. In wild-type larvae, branches of the same class IV dendritic arborization neuron achieve efficient coverage of its two-dimensional receptive field with minimum overlap with each other. However, this self-avoidance was disrupted in a fmi hypomorphic mutant, in an esn knockout homozygote, and in the fmi/esn trans-heterozygote. A functional fusion protein, Fmi:3eGFP, was localized at most of the branch tips, and in a heterologous system, assembly of Esn at cell contact sites required its LIM domain and Fmi. We further show that genes controlling epithelial planar cell polarity (PCP), such as Van Gogh (Vang) and RhoA, are also necessary for the self-avoidance, and that fmi genetically interacts with these loci. On the basis of these and other results, we propose that the Fmi-Esn complex, together with the PCP regulators and the Tricornered (Trc) signaling pathway, executes the repulsive interaction between isoneuronal dendritic branches.

Root exudation in a sloping Moso bamboo forest in relation to fine root biomass and traits.

Exudation by fine roots generally varies with their morphological traits, but the effect of belowground resource availability on the root exudation via root morphological traits and biomass remains unknown. We aimed to determine the effects of morphological and physiological traits on root exudation rates and to estimate stand-scale exudation (Estand) by measuring the mass, length, and surface area of fine roots in a Moso bamboo forest. We measured root exudation as well as morphological and physiological traits in upper and lower plots on a slope with different belowground resource availability. The mean (± S.D.) root exudation rates per mass in the upper and lower slope were 0.049 ± 0.047 and 0.040 ± 0.059 mg C g-1 h-1, respectively, which were in the range of exudation found in woody forest ecosystems. We observed significant relationships between root exudation per mass and root respiration, as well as specific root length and surface area. In contrast, exudation per length and area did not correlate with morphological traits. The morphological traits did not differ between slope positions, resulting in no significant difference in root exudation per mass. Fine root biomass, length, and surface area on a unit ground basis were much higher in the lower than those in the upper slope positions. Estand was higher when estimated by mass than by length and area because the morphological effect on exudation was ignored when scaled using mass. Estand was 1.4-2.0-fold higher in the lower than that in upper slope positions, suggesting that the scaling parameters of mass, length, and area determined the Estand estimate more than the exudation rate per mass, length, and area. Regardless of scaling, Estand was much higher in the Moso bamboo forest than in other forest ecosystems because of a large fine-root biomass.

Computational modeling of dendritic tiling by diffusible extracellular suppressor.

The development of neuronal class-specific dendrites is a basis for the correct functioning of the nervous system. For instance, tiling of dendritic arbors (complete, but minimum-overlapping innervation of a field) supports uniform reception of input stimuli. Previous studies have attempted to show the molecular and cellular basis of tiling, and it has been argued that the underlying inhibitory interaction between dendrites is realized by contact-dependent retraction and/or by repulsion of dendrites via extracellular branch suppressors. In this study, we showed that the development and regeneration of the tiling pattern could be reproduced by two different mathematical models (the cell compartment model and the end capped-segment model), in both of which dendrite growth is coupled with the dynamics of an extracellular suppressor that is secreted from dendrites. The analysis of the end capped-segment model in three-dimensional space showed that it generated both non-overlapping arbors as well as overlapping dendritic arbors, which patterns are reminiscent of phenotypes of previously reported tiling mutants in vivo. Moreover, the results of our numerical analysis of the 2 models suggest that tiling patterns could be achieved either by a local increase in the concentration of an intracellular branching activator or by a local decrease in the production of a suppressor at branch ends.

Self-organizing mechanism for development of space-filling neuronal dendrites.

Neurons develop distinctive dendritic morphologies to receive and process information. Previous experiments showed that competitive dendro-dendritic interactions play critical roles in shaping dendrites of the space-filling type, which uniformly cover their receptive field. We incorporated this finding in constructing a new mathematical model, in which reaction dynamics of two chemicals (activator and suppressor) are coupled to neuronal dendrite growth. Our numerical analysis determined the conditions for dendritic branching and suggested that the self-organizing property of the proposed system can underlie dendritogenesis. Furthermore, we found a clear correlation between dendrite shape and the distribution of the activator, thus providing a morphological criterion to predict the in vivo distribution of the hypothetical molecular complexes responsible for dendrite elongation and branching.

An eye tracking system for monitoring face scanning patterns reveals the enhancing effect of oxytocin on eye contact in common marmosets.

Eye tracking systems are used to investigate eyes position and gaze patterns presumed as eye contact in humans. Eye contact is a useful biomarker of social communication and known to be deficient in patients with autism spectrum disorders (ASDs). Interestingly, the same eye tracking systems have been used to directly compare face scanning patterns in some non-human primates to those in human. Thus, eye tracking is expected to be a useful translational technique for investigating not only social attention and visual interest, but also the effects of psychiatric drugs, such as oxytocin, a neuropeptide that regulates social behavior. In this study, we report on a newly established method for eye tracking in common marmosets as unique New World primates that, like humans, use eye contact as a mean of communication. Our investigation was aimed at characterizing these primates face scanning patterns and evaluating the effects of oxytocin on their eye contact behavior. We found that normal common marmosets spend more time viewing the eyes region in common marmoset's picture than the mouth region or a scrambled picture. In oxytocin experiment, the change in eyes/face ratio was significantly greater in the oxytocin group than in the vehicle group. Moreover, oxytocin-induced increase in the change in eyes/face ratio was completely blocked by the oxytocin receptor antagonist L-368,899. These results indicate that eye tracking in common marmosets may be useful for evaluating drug candidates targeting psychiatric conditions, especially ASDs.

An evolutionarily conserved protein CHORD regulates scaling of dendritic arbors with body size.

Most organs scale proportionally with body size through regulation of individual cell size and/or cell number. Here we addressed how postmitotic and morphologically complex cells such as neurons scale with the body size by using the dendritic arbor of one Drosophila sensory neuron as an assay system. In small adults eclosed under a limited-nutrition condition, the wild-type neuron preserved the branching complexity of the arbor, but scaled down the entire arbor, making a "miniature". In contrast, mutant neurons for the Insulin/IGF signaling (IIS) or TORC1 pathway exhibited "undergrowth", which was characterized by decreases in both the branching complexity and the arbor size, despite a normal diet. These contrasting phenotypes hinted that a novel regulatory mechanism contributes to the dendritic scaling in wild-type neurons. Indeed, we isolated a mutation in the gene CHORD/morgana that uncoupled the neuron size and the body size: CHORD mutant neurons generated miniature dendritic arbors regardless of the body size. CHORD encodes an evolutionarily conserved co-chaperone of HSP90. Our results support the notion that dendritic growth and branching are controlled by partly separate mechanisms. The IIS/TORC1 pathways control both growth and branching to avert underdevelopment, whereas CHORD together with TORC2 realizes proportional scaling of the entire arbor.

Sensory-neuron subtype-specific transcriptional programs controlling dendrite morphogenesis: genome-wide analysis of Abrupt and Knot/Collier.

The transcription factors Abrupt (Ab) and Knot (Kn) act as selectors of distinct dendritic arbor morphologies in two classes of Drosophila sensory neurons, termed class I and class IV, respectively. We performed binding-site mapping and transcriptional profiling of these isolated neurons. Their profiles were similarly enriched in cell-type-specific enhancers of genes implicated in neural development. We identified a total of 429 target genes, of which 56 were common to Ab and Kn; these targets included genes necessary to shape dendritic arbors in either or both of the two sensory subtypes. Furthermore, a common target gene, encoding the cell adhesion molecule Ten-m, was expressed more strongly in class I than class IV, and this differential was critical to the class-selective directional control of dendritic branch sprouting or extension. Our analyses illustrate how differentiating neurons employ distinct and shared repertoires of gene expression to produce class-selective morphological traits.

Multidendritic sensory neurons in the adult Drosophila abdomen: origins, dendritic morphology, and segment- and age-dependent programmed cell death.

BACKGROUND: For the establishment of functional neural circuits that support a wide range of animal behaviors, initial circuits formed in early development have to be reorganized. One way to achieve this is local remodeling of the circuitry hardwiring. To genetically investigate the underlying mechanisms of this remodeling, one model system employs a major group of Drosophila multidendritic sensory neurons - the dendritic arborization (da) neurons - which exhibit dramatic dendritic pruning and subsequent growth during metamorphosis. The 15 da neurons are identified in each larval abdominal hemisegment and are classified into four categories - classes I to IV - in order of increasing size of their receptive fields and/or arbor complexity at the mature larval stage. Our knowledge regarding the anatomy and developmental basis of adult da neurons is still fragmentary. RESULTS: We identified multidendritic neurons in the adult Drosophila abdomen, visualized the dendritic arbors of the individual neurons, and traced the origins of those cells back to the larval stage. There were six da neurons in abdominal hemisegment 3 or 4 (A3/4) of the pharate adult and the adult just after eclosion, five of which were persistent larval da neurons. We quantitatively analyzed dendritic arbors of three of the six adult neurons and examined expression in the pharate adult of key transcription factors that result in the larval class-selective dendritic morphologies. The 'baseline design' of A3/4 in the adult was further modified in a segment-dependent and age-dependent manner. One of our notable findings is that a larval class I neuron, ddaE, completed dendritic remodeling in A2 to A4 and then underwent caspase-dependent cell death within 1 week after eclosion, while homologous neurons in A5 and in more posterior segments degenerated at pupal stages. Another finding is that the dendritic arbor of a class IV neuron, v'ada, was immediately reshaped during post-eclosion growth. It exhibited prominent radial-to-lattice transformation in 1-day-old adults, and the resultant lattice-shaped arbor persisted throughout adult life. CONCLUSION: Our study provides the basis on which we can investigate the genetic programs controlling dendritic remodeling and programmed cell death of adult neurons, and the life-long maintenance of dendritic arbors.