Constraints and Opportunities for Development of Grasslands in Urban Areas of the Niayes Zone in Senegal

A survey was carried out in urban areas of the Niayes zone in Senegal to explore grasslands development in agropastoral systems around towns. Rapid rural appraisal and farms multiple visits were done to describe the forage cropping system, identify constraints and opportunities of developing grasslands in urban areas. In Niayes urban areas, forage production system is being developed based on the cropping of several grass and tree species. Only a minority of farmers is involved in that activity. Level of grass production is rather low. Weak development of grasslands is observed. Main reasons are: farmer poor willingness to crop for livestock feeding, lack of water and production factors including seeds and fertiliser, land tenure system and lack of integration between livestock and horticulture, security and economical environment. There are opportunities that need to be developed for improvement of grassland production in the Niayes as water reserves could tolerate more forage cropping. Research and development programs should focus on programs that could generate recommendations on grasslands development in association with horticulture witch is a major activity in Niayes areas

Cell-cycle dependent organization and dynamics of RNA Polymerase I in live human cells

RNA Polymerase I (Pol I) is responsible for over 60% of transcriptional output in human cells, yet basic questions concerning the spatial and temporal organization of the polymerase remain unanswered. Here we investigate how mammalian cells rely on Pol I organization throughout the cell cycle to balance different needs, from complete transcription shut down to massive increase in protein synthesis (and thus ribosomal RNA synthesis) before cell division. In contrast to our previous reports on RNA Polymerase II, Pol I clusters are stable with active transcription, and the presence of transient Pol I clusters correlates with inactive ribosomal transcription. Our results suggest that both stable and transient populations Pol I clusters co-exist in individual living cells, and their relative fraction may directly reflect the global gene expression need of the cell

Voices in methods development

To mark the 15th anniversary of Nature Methods, we asked scientists from across diverse fields of basic biology research for their views on the most exciting and essential methodological challenges that their communities are poised to tackle in the near future

Voices in methods development

To mark the 15th anniversary of Nature Methods, we asked scientists from across diverse fields of basic biology research for their views on the most exciting and essential methodological challenges that their communities are poised to tackle in the near future

Nuclear target search at the single molecule level: protein interactions define the exploration landscape

Gene regulation relies on highly mobile transcription factors (TFs) exploring the nucleoplasm in search of their targets. Our view of the nucleus has evolved from that of an isotropic and homogenous reactor to that of a highly organized yet very dynamic organelle. However important questions remain on how these regulatory factors explore the nuclear environment in search of their DNA or protein targets, and how their exploration strategy affects the kinetics of transcriptional regulation. We implemented a single-molecule tracking assay to determine the TFs dynamics using photoactivatable tags in human cells. We investigated the mobility of several nuclear proteins, including the transcription factor c-Myc and the elongation factor P-TEFb. We found that, while their diffusion speed was comparable, these proteins largely differed in terms of their exploration geometry. We discovered that c-Myc is a global explorer diffusing in the nucleus without spatial constraints. In contrast, the positive transcription elongation factor P-TEFb is a local explorer that oversamples its environment, constrained by a fractal nuclear architecture. Consequently, each c-Myc molecule is equally available for all nuclear sites while P-TEFb reaches its targets in a position-dependent manner. We also measured the mobility of a P-TEFb mutant in which the interaction with the CTD of the RNA Pol II was truncated. In this case, the single-molecule experiments suggested a global exploration of the P-TEFb mutant, consistent with free diffusion. Our observations are in line with a model in which the exploration geometry of TFs is constrained by their interactions and not by exclusion properties. Our findings have strong implications on how proteins react in the nucleus and how their function can be regulated in space and time