Molecular mechanisms of spider silk

Spiders spin high-performance silks through the expression and assembly of tissue-restricted fibroin proteins. Spider silks are composite protein biopolymers that have complex microstructures. Retrieval of cDNAs and genomic DNAs encoding silk fibroins has revealed an association between the protein sequences and structure-property relationships. However, before spider silks can be subject to genetic engineering for commercial applications, the complete protein sequences and their functions, as well as the details of the spinning mechanism, will require additional progress and collaborative efforts in the areas of biochemistry, molecular biology and material science. Novel approaches to reveal additional molecular constituents embedded in the spider fibers, as well as cloning strategies to manipulate the genes for expression, will continue to be important aspects of spider biology research. Here we summarize the molecular characteristics of the different spider fibroins, the mechanical properties and assembly process of spidroins and the advances in protein expression systems used for recombinant silk production. We also highlight different technical approaches being used to elucidate the molecular constituents of silk fibers. Received 28 February 2006; received after revision 14 April 2006; accepted 22 May 2006 X. Hu and K. Vasanthavada contributed equally to this work.     

A diffusion model for products with indirect network externalities

This paper develops a new diffusion model that incorporates the indirect network externality. The market with indirect network externalities is characterized by two‐way interactive effects between hardware and software products on their demands. Our model incorporates two‐way interactions in forecasting the diffusion of hardware products based on a simple but realistic assumption. The new model is parsimonious, easy to estimate, and does not require more data points than the Bass diffusion model. The new diffusion model was applied to forecast sales of DVD players in the United States and in South Korea, and to the sales of Digital TV sets in Australia. When compared to the Bass and NSRL diffusion models, the new model showed better performance in forecasting long‐term sales. Copyright © 2008 John Wiley & Sons, Ltd.     

扬子鳄产蛋与天气关系的研究

本文报道了扬子鳄的生殖能力与其在人工饲养下小生境气候之间的关系。５年的研究表明：扬子鳄的产蛋期通常在七月上中旬。这时期的最低平均温度为２５．９°Ｃ，最高平均温度为２８．６°Ｃ，降雨量为６７．３～８１．４ｍｍ。但是当气候变化时会影响扬子鳄的产蛋时间和产蛋窝数     

蛋鸡及其正反杂交组合卵巢组织的基因差异显示研究

在杂交试验中发现：白莱航蛋鸡（AA）与农大褐蛋鸡（DD）的正交组合（AD）和反交组合（DA）鸡群在产蛋数上存在着明显的杂种优势.为了探明产蛋数杂种优势的遗传机理，研究了4个组合鸡群在产蛋高峰期（32周龄）卵巢组织的基因差异显示.结果表明，24种引物组合在4个试验鸡群的RNA池中共显示出726条稳定的cDNA条带，其中112（15.43%）条为差异带.在杂种与纯种间共发现7类基因差异表达模式，其中量的差异有2类：Ⅰ杂种超强（T1++1，T1+11，T11+1）表达17条（15.17%）；Ⅱ杂种减弱（T1 1，T1 11，T11 1）表达15条（13.39%）；质的差异表达模式有5类：Ⅲ杂种沉默型（T1001、T1011、T1101）9条（8.04%）；Ⅳ杂种特异型（T0110、T0100、T0010）7条（6.25%）；Ⅴ杂种与单亲一致（T1110、T0111、T1100、T1010、T0101、T0011）型58条（51.78%）；Ⅵ共显性（T+11 、T 11+）6条（5.36%）；Ⅶ杂种与双亲一致型（T1111）614条（84.57%）.试验结果表明4个组合鸡群在产蛋高峰期的卵巢组织中存在着明显的基因表达差异.     

黄头脊鸟令鸟产卵能学的研究

在自然生长状态下,用测定在黄头JieLing（Motacilla citreola）成鸟产卵期性腺及输卵管蛋的质量变化的方法,研究了它们在产卵期间的能量投入及其分配形式,产卵期,雌鸟用于性腺增长和卵形成的能量预算为66．24－71．19kJ,其中用于蛋白质和脂肪的能量分别为40．42KJ和25．82-30．78KJ,占总能量预算的56．8％－61．0％和36．3％－46．5％,用于繁殖蛋白的能量分配为：输卵管2．77KJ,卵黄蛋白12．80KJ,卵白蛋白24．85KJ,雌鸟耗能最大的是第0d－＋1d,达（13．28－14．26）KJ／d,产卵期雄耗能（用于性腺增长）7．98KJ,雌雄亲鸟用于卵的形成和性腺增长共投入能量74．22－79．17KJ,雌鸟耗能为雄鸟的8．3倍－8．9倍。     

超临界二氧化碳萃取蛋黄油的工艺研究

用超临界二氧化碳萃取技术,在比较温和的实验条件下,从蛋黄粉中分离出蛋黄油。通过正交实验确定了较佳的工艺参数为：萃取压力24Mpa,萃取温度50℃,萃取时间5h,在此条件下,蛋黄油的萃取率可达80.1%。     

利用乙醇萃取卵黄油的试验研究

通过采用乙醇溶剂提取蛋黄粉中的卵黄油 研究了工艺参数对卵黄油及磷脂提取率的影响 试验表明 :温度和乙醇浓度对卵黄油的提取率影响较大 ;温度、作用时间和乙醇添加量是影响磷脂提取率的主要因素     

Specific degradation of keratin in Xenopus laevis egg extracts undergoing apoptosis

Cytochrome c activates apoptosis specific protease XCPP32 when being added to Xenopus laevis egg extracts, and induces apoptosis in this cell-free system. During apoptosis, cyto-skeleton proteins in egg extracts are degraded. Western blot assay indicates that 42-ku acidic keratin in egg extracts has been degraded by XCPP32. The degradation of 42-ku keratin may be crucial in apoptosis.     

Hatching phenology,life history and population dynamics of the Oriental clam shrimp Eulimnadia indocylindrova Durga Prasad and Simhachalam with notes on phenology patterns in the Spinicaudata

We studied the natural history, hatching phenology and egg bank composition of the Oriental spinicaudatan clam shrimp Eulimnadia indocylindrova Durga Prasad and Simhachalam using both field studies and ex situ sediment rehydration. Field observations revealed that hatching began very early (1–2 days) after inundation, and continued for about 5 days. Mature adults could be observed by 10 days, and they survived up to 16 days. The population showed a largely hermaphrodite-biased sex ratio (male:hermaphrodite 1:3) observed over three years, with a decrease in number of males throughout the hydroperiod. Both amphigenic and monogenic hermaphrodites were observed. The total lifetime fecundity recorded was about 300 eggs laid in multiple clutches. The egg bank composition showed a high proportion of intact eggs, indicative of predictable hydrations and low sediment adversity. Hatching began on the first day post-inundation for all successive cyclical hydration treatments, with peak hatching on days 2 and 3. Hatching rate was highest (57% of total hatching in successive cycles) for the first hydration, decreasing subsequently for the further hydrations. Hatching duration decreased with successive hydrations and was the longest (around 7 days) for the first hydration. Maximum hatching (93%) occurred in the first 10 days for the continuous hydration treatment. Overall, the total emergence of nauplii in successive hydrations was larger than that observed for the continuous hydration treatment, indicative of a risk-spreading strategy across hydroperiods. Early and concentrated naupliar emergence, along with decreased hatching durations for successive cycles, was observed for all the hydrations. A survey of literature revealed a general lack of data on hatching phenology of clam shrimps, particularly from tropical and sub-tropical regions. Based on the available data, it appears that hatching patterns, particularly high, early hatching fractions, are commonly observed in Spinicaudata species, and do not seem to differ much across biogeographical regions.     

电晕技术与家蚕的人工孵化──对冷藏蚕种的影响研究

通过对蚕种的盐酸浸泡来实现家蚕的人工孵化是国内外蚕桑业普遍采用的方法，它的优点是孵化效果好，但缺点是成本较高，处理的要求较严，最令人烦恼的是盐酸会对环境产生污染，影响操作人员的健康。作者用电晕技术对冷藏蚕种进行处理，发现蚕卵的孵化率不亚于浸酸处理的对照组，而且还发现，电晕对丙２、丁１期胚子进行短时间的刺激后，再送回冷库冷藏４－７天，可以取得同样的孵化效果。