Feedback loops shape cellular signals in space and time

Positive and negative feedback loops are common regulatory elements in biological signaling systems. We discuss core feedback motifs that have distinct roles in shaping signaling responses in space and time. We also discuss approaches to experimentally investigate feedback loops in signaling systems.     

Xenopus laevis in developmental and molecular biology

Xenopus laevis is a prime system for the study of embryogenesis in vertebrates. Both prelocalized information in the egg and inductive interactions between cells contribute to the ordered increase in complexity during development. Embryonic induction, discovered in amphibians, is being studied intensely in Xenopus; recent work suggests a role for growth factors in this process. Contributions of the Xenopus system to the analysis of ribosomal and 5S RNA genes, and the diverse and highly productive applications of the oocyte injection technology, are also summarized.     

From genotype to phenotype: systems biology meets natural variation

The promise that came with genome sequencing was that we would soon know what genes do, particularly genes involved in human diseases and those of importance to agriculture. We now have the full genomic sequence of human, chimpanzee, mouse, chicken, dog, worm, fly, rice, and cress, as well as those for a wide variety of other species, and yet we still have a lot of trouble figuring out what genes do. Mapping genes to their function is called the "genotype-to-phenotype problem," where phenotype is whatever is changed in the organism when a gene's function is altered.     

百合鳞茎发育生物学研究进展

百合是重要的鲜切花,也可以做盆花,还可以在园林中应用。要生产出优质的百合切花,需要优良的百合种球,生产出优质种球需要对百合鳞茎的发育生物学深入了解。在阐述了百合鳞茎生长发育特点的基础上,对其生长发育过程中重要的生理生化变化进行了综述,其中包括鳞茎中淀粉含量变化、淀粉代谢的关键酶、可溶性糖及蛋白质的相关研究进展,并就今后鳞茎发育研究趋势进行了展望。      

Reinterpreting space, time lags, and functional responses in ecological models

Natural enemy-victim interactions are of major applied importance and of fundamental interest to ecologists. A key question is what stabilizes these interactions, allowing the long-term coexistence of the two species. Three main theoretical explanations have been proposed: behavioral responses, time-dependent factors such as delayed density dependence, and spatial heterogeneity. Here, using the powerful moment-closure technique, we show a fundamental equivalence between these three elements. Limited movement by organisms is a ubiquitous feature of ecological systems, allowing spatial structure to develop; we show that the effects of this can be naturally described in terms of time lags or within-generation functional responses.     

荔枝采后生物学研究及其在广西的发展现状

文章综述了国内外荔枝采后生理及贮藏保鲜机理研究进展,指出失水和果皮褐变是荔枝贮藏保鲜研究的重点和难点。结合广西荔枝生产和采后生物学研究现状,提出借鉴国内外荔枝采后生物学研究经验,结合广西特色荔枝资源及品种特性,进一步加强地方特色品种采后生物学研究,系统掌握品种成熟和衰老生理、低温伤害生理及气调生理等新理论,研发适合广西农业生产需要的实用型贮藏保鲜技术等建议,以促进广西荔枝采后保鲜向特色化和多样化方向发展。     

Multimodal signals: enhancement and constraint of song motor patterns by visual display

Many birds perform visual signals during their learned songs, but little is known about the interrelationship between visual and vocal displays. We show here that male brown-headed cowbirds (Molothrus ater) synchronize the most elaborate wing movements of their display with atypically long silent periods in their song, potentially avoiding adverse biomechanical effects on sound production. Furthermore, expiratory effort for song is significantly reduced when cowbirds perform their wing display. These results show a close integration between vocal and visual displays and suggest that constraints and synergistic interactions between the motor patterns of multimodal signals influence the evolution of birdsong.     

Three-dimensional mapping of dislocation avalanches: clustering and space/time coupling

There is growing evidence for the complex, intermittent, and heterogeneous character of plastic flow. Here we report a three-dimensional mapping of dislocation avalanches during creep deformation of an ice crystal, from a multiple-transducers acoustic emission analysis. Correlation analysis shows that dislocation avalanches are spatially clustered according to a fractal pattern and that the closer in time two avalanches are, the larger the probability is that they will be closer in space. Such a space/time coupling may contribute to the self-organization of the avalanches into a clustered pattern.     

Integrating space and time: a case for phenological context in grazing studies and management

In water-limited landscapes, patterns in primary production are highly variable across space and time. Livestock grazing is a common agricultural practice worldwide and a concern is localized overuse of specific pasture resources that can exacerbate grass losses and soil erosion. On a research ranch in New Mexico with average annual rainfall of 217 mm, we demonstrate with a quantitative approach that annual seasons vary greatly and examine foraging patterns in Angus-Hereford (Bos taurus) cows. We define five seasonal stages based on MODIS NDVI: pre-greenup, greenup, peak green, drydown and dormant, and examine livestock movements in 2008. Daily distance traveled by cows was greater and foraging area expanded during periods with higher precipitation. A regression model including minimum NDVI, rainfall and their interaction explained 81% of the seasonal variation in distance traveled by cows (P<0.01). Cows explored about 81 ha·d⁻¹ while foraging, but tended to explore smaller areas as the pasture became greener (greenup and peak green stages). Cows foraged an average of 9.7 h daily and spent more time foraging with more concentrated search patterns as pastures became greener. Our findings suggest that phenological context can expand the capacity to compare and integrate findings, and facilitate meta-analyses of grazing studies conducted at different locations and times of year.