Molecular strategies in the evolution of mammalian dental patterning

The acquisition of masticatory capability by mammals allowed a better processing of food and a consequent increase in the efficiency of nutrients intake by the digestive system. The development of tooth classes and variations in tooth number can be considered intrinsic characteristics of mammalian dentition. These features allowed species to develop specialized dentitions, creating new adaptive zones. Comparative developmental data from knockout mutant mice and human tooth agenesis present new insights on the molecular strategies that permitted rapid phenotypic differentiation, adaptation and speciation of mammalian dentition.     

Copy Number of Ribosomal Operons in Prokaryotes and Its Effect on Phylogenetic Analyses

Different aspects of the presence of multiple copies of ribosomal operons in prokaryotic genomes are reviewed. The structure of prokaryotic ribosomal operons is briefly described. The available data are summarized regarding the copy number of ribosomal genes in various prokaryotic genomes, the degree of polymorphism of their individual copies, and physiological and evolutional aspects of the presence of the multiple copies of ribosomal genes. The review also considers the influence of the presence of multiple copies of ribosomal genes on the results of identification of prokaryotic isolates and of the studies of prokaryotic diversity in environmental samples based on phylogenetic analysis of 16S rRNA gene sequences.     

Echo delay versus spectral cues for temporal hyperacuity in the big brown bat,Eptesicus fuscus

Big brown bats can discriminate between echoes that alternate in delay (jitter) by as little as 10–15 ns and echoes that are stationary in delay. This delay hyperacuity seems so extreme that it has been rejected in favor of an explanation in terms of artifacts in echoes, most likely spectral in nature, that presumably are correlated with delay. Using different combinations of digital, analog, and cable delays, we dissociated the overall delay of jittering echoes from the size of the analog component of delay, which alone is presumed to determine the strength of the apparatus artifact. The bats' performance remains invariant with respect to the overall delay of the jittering echoes, not with respect to the amount of analog delay. This result is not consistent with the possible use of delay-related artifacts produced by the analog delay devices. Moreover, both electronic and acoustic measurements disclose no spectral cues or impedance-mismatch reflections in delayed signals, just time-delays. The absence of artifacts from the apparatus and the failure of overlap and interference from reverberation to account for the 10-ns result means that closing the gap between the level of temporal accuracy plausibly explained from physiology and the level observed in behavior may require a better understanding of the physiology.Abbreviations FM frequency-modulated - XCR cross-correlation function     

Characteristics associated with Woolly Apple Aphid Eriosoma lanigerum, resistance of three apple rootstocks

The resistance characteristics of the apple resistance genes (Er1, Er2, and Er3) to the woolly apple aphid, Eriosoma lanigerum (Hausmann) (Homoptera: Aphididae) were studied according to the performance measured on apple cultivars containing these resistance genes. The resistance characteristics of Northern Spy (Er1), Robusta 5 (Er2), and Aotea (Er3) were compared to the susceptible cultivar Royal Gala, by measuring the aphid settlement, development, and survival rates correlated with electronically monitored probing behaviour. Er1 and Er2 had a higher level of resistance with a significantly shorter period of phloem feeding, suggesting that the resistance factors were present in the phloem tissue. Phenological measurements indicated that the aphids showed poor settlement, development, and survival on Er2. Er1 also showed low settlement and survival, although not as low as Er2. Aphid performance and feeding on Aotea (Er3) were similar to Royal Gala, suggesting that some woolly apple aphids in New Zealand may have recently overcome Er3 resistance. The differences in resistance mechanisms of Er1, Er2, and Er3 are discussed in relation to the strategy of pyramiding these genes to give a durable resistance to woolly apple aphid.     

Evolutionary conservation and DNA binding properties of the Ssh7 proteins from Sulfolobus shibatae

The thermoacidophilic archaeon Sulfolobus shibatae synthesizes a large amount of the 7-ku DMA binding proteins known as Ssh7. Our hybridization experiments showed that two Ssh7-encoding genes existed in the genome of S. shibatae. These two genes, designated ssh7a and ssh7b, have been cloned, sequenced and expressed in Escherichia coli. The two Ssh7 proteins differ only at three amino acid positions. In addition, the cis-regulatory sequences of the ssh7a and ssh7b genes are highly conserved. These results suggest the presence of a selective pressure to maintain not only the sequence but also the expression of the two genes. We have also found that there are two genes encoding the 7-ku protein in Sulfolobus solfataricus. Based on this and other studies, we suggest that the gene encoding the 7-ku protein underwent duplication before the separation of Sulfolobus species. Binding of native Ssh7 and recombinant (r)Ssh7 to short duplex DNA fragments was analyzed by electrophoretic mobility shift assays. Both n     

The Human Obesity Gene Map: The 2001 Update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.     

可变剪接在植物免疫中的研究进展

可变剪接是生物重要的转录后修饰过程,是转录组和蛋白组多样性的重要来源.可变剪接参与了植物众多生理过程,包括植物昼夜节律、生长发育等,在植物响应生物和非生物胁迫过程中尤为普遍.近年来,可变剪接被认为是植物抵御病原菌侵染的重要调控机制.本文综述了可变剪接在植物免疫各个层面的调控作用,包括调节重要免疫受体、R基因、激素信号路...