Summing up the noise in gene networks

Random fluctuations in genetic networks are inevitable as chemical reactions are probabilistic and many genes, RNAs and proteins are present in low numbers per cell. Such 'noise' affects all life processes and has recently been measured using green fluorescent protein (GFP). Two studies show that negative feedback suppresses noise, and three others identify the sources of noise in gene expression. Here I critically analyse these studies and present a simple equation that unifies and extends both the mathematical and biological perspectives.     

Observation of coherent optical information storage in an atomic medium using halted light pulses

Electromagnetically induced transparency is a quantum interference effect that permits the propagation of light through an otherwise opaque atomic medium; a 'coupling' laser is used to create the interference necessary to allow the transmission of resonant pulses from a 'probe' laser. This technique has been used to slow and spatially compress light pulses by seven orders of magnitude, resulting in their complete localization and containment within an atomic cloud. Here we use electromagnetically induced transparency to bring laser pulses to a complete stop in a magnetically trapped, cold cloud of sodium atoms. Within the spatially localized pulse region, the atoms are in a superposition state determined by the amplitudes and phases of the coupling and probe laser fields. Upon sudden turn-off of the coupling laser, the compressed probe pulse is effectively stopped; coherent information initially contained in the laser fields is 'frozen' in the atomic medium for up to 1 ms. The coupling laser is turned back on at a later time and the probe pulse is regenerated: the stored coherence is read out and transferred back into the radiation field. We present a theoretical model that reveals that the system is self-adjusting to minimize dissipative loss during the 'read' and 'write' operations. We anticipate applications of this phenomenon for quantum information processing.     

A mouse gene related to Distal-less shows a restricted expression in the developing forebrain.

Many genes known to be involved in embryogenesis and morphogenesis of the fruitfly Drosophila melanogaster encode proteins with a highly conserved region of 60 amino acids called the homeodomain. Mammalian counterparts for most of these genes have been identified, including those homologous to the Drosophila homeotic genes or to genes such as evenskipped, engrailed or caudal. We have isolated a murine homeobox gene that encodes a homeodomain similar to that encoded by the Drosophila Distalless (Dll) gene. Dll has a crucial role in Drosophila limb morphogenesis, partially specifying pattern along the proximo-distal axis of the limb. The murine counterpart is expressed in a restricted region of the developing brain, within the diencephalon and the adjacent telencephalic regions.     

Low gene copy number shows that arbuscular mycorrhizal fungi inherit genetically different nuclei

Arbuscular mycorrhizal fungi (AMF) are ancient asexually reproducing organisms that form symbioses with the majority of plant species, improving plant nutrition and promoting plant diversity. Little is known about the evolution or organization of the genomes of any eukaryotic symbiont or ancient asexual organism. Direct evidence shows that one AMF species is heterokaryotic; that is, containing populations of genetically different nuclei. It has been suggested, however, that the genetic variation passed from generation to generation in AMF is simply due to multiple chromosome sets (that is, high ploidy). Here we show that previously documented genetic variation in Pol-like sequences, which are passed from generation to generation, cannot be due to either high ploidy or repeated gene duplications. Our results provide the clearest evidence so far for substantial genetic differences among nuclei in AMF. We also show that even AMF with a very large nuclear DNA content are haploid. An underlying principle of evolutionary theory is that an individual passes on one or half of its genome to each of its progeny. The coexistence of a population of many genomes in AMF and their transfer to subsequent generations, therefore, has far-reaching consequences for understanding genome evolution.     

大熊猫电刺激采精及精液冷冻保存研究

对卧龙自然保护区大熊猫研究中心的９只５．５－１６．５岁的雄性大熊猫进行了１７次电刺激采精,其中３只是能进行自然交配并繁殖了后代的种公兽,比较研究了精液离心、不同稀释液和冷冻方法对大熊猫精液超低温冷冻保存后的活力、运动状态、精子和顶体形态的影响。细冷冻是１种较好的超低温冷冻精液的方法。     

加入WTO后庆加快信息资源的建设

文章就我国加入WTO后信息资源建设方面的必要性、紧迫性、实用性、目标等方面做了阐述。     

改革开放以来的利益集团与中国政治发展

改革开放以来,利益集团在中国政治发展进程中的作用已经很重要了。中国利益集团有其特定的概念、历史、特征,在它对中国政治发展起作用的过程中,也出现了一些问题。但要充分认识到利益集团存在的必然性、合理性,通过政府与社会的共同作用,发挥和完善利益集团对中国政治发展的积极影响。