A role for the RNase III enzyme DCR-1 in RNA interference and germ line development in Caenorhabditis elegans

An early event in RNA interference (RNAi) is the cleavage of the initiating double-stranded RNA (dsRNA) to short pieces, 21 to 23 nucleotides in length. Here we describe a null mutation in dicer-1 (dcr-1), a gene proposed to encode the enzyme that generates these short RNAs. We find that dcr-1(-/-) animals have defects in RNAi under some, but not all, conditions. Mutant animals have germ line defects that lead to sterility, suggesting that cleavage of dsRNA to short pieces is a requisite event in normal development.     

短尾鮠精子细胞和精子的超微结构研究

用透射电镜观察了短尾鮠精子细胞和精子的形态以及细胞核、拟染色体和线粒体等的结构变化规律。结果表明,随着精子细胞的发育,核质凝聚程度逐渐增强。精子细胞时期细胞器较丰富,到精子细胞后期,细胞器的形态和数量发生了较大变化。短尾鮠的精子具有椭圆的头部和复杂的中片;近侧中心粒和远侧中心粒靠近核的中央;鞭毛呈9+2轴丝结构,并具有由外膜折迭形成的波浪形的鳍状结构。     

An improved solution for the infiltration advance problem in irrigation hydraulics

The irrigation advance problem in irrigation hydraulics has been spread across the engineering and soil science literature over a number of decades. The Lewis–Milne framework has been used extensively, but one problem has been to find a suitable infiltration equation. The infiltration advance solutions of Philip and Farrell, and Collis-George and Freebairn are compared to a new solution based on the linear soil infiltration equation. It is shown that the linear soil solution is able to give similar results to the Philip and Farrell solution at early stages of infiltration when this is valid, and the Collis-George and Freebairn solution at longer times when this is valid. The linear soil infiltration advance solution presented here is the first using physically meaningful parameters which is able to give adequate infiltration and advance behaviour over all time scales. To further test the linear soil concept, we inversely fit irrigation advance data to get the sorptivity, saturated hydraulic conductivity and infiltration rate behaviour of the soil using all three infiltration equations. The linear soil is shown to give the best fit for the infiltration behaviour to the measured results with an average r ² of 0.98 compared to 0.84 for Philip and Farrell and 0.77 for Collis-George and Freebairn. The linear soil model was also the best fit using other statistical tests such as RMSE and RSR.