Independent evolution of striated muscles in cnidarians and bilaterians

Striated muscles are present in bilaterian animals (for example, vertebrates, insects and annelids) and some non-bilaterian eumetazoans (that is, cnidarians and ctenophores). The considerable ultrastructural similarity of striated muscles between these animal groups is thought to reflect a common evolutionary origin. Here we show that a muscle protein core set, including a type II myosin heavy chain (MyHC) motor protein characteristic of striated muscles in vertebrates, was already present in unicellular organisms before the origin of multicellular animals. Furthermore, 'striated muscle' and 'non-muscle' myhc orthologues are expressed differentially in two sponges, compatible with a functional diversification before the origin of true muscles and the subsequent use of striated muscle MyHC in fast-contracting smooth and striated muscle. Cnidarians and ctenophores possess striated muscle myhc orthologues but lack crucial components of bilaterian striated muscles, such as genes that code for titin and the troponin complex, suggesting the convergent evolution of striated muscles. Consistently, jellyfish orthologues of a shared set of bilaterian Z-disc proteins are not associated with striated muscles, but are instead expressed elsewhere or ubiquitously. The independent evolution of eumetazoan striated muscles through the addition of new proteins to a pre-existing, ancestral contractile apparatus may serve as a model for the evolution of complex animal cell types.     

Interactions between cancer stem cells and their niche govern metastatic colonization

Metastatic growth in distant organs is the major cause of cancer mortality. The development of metastasis is a multistage process with several rate-limiting steps. Although dissemination of tumour cells seems to be an early and frequent event, the successful initiation of metastatic growth, a process termed 'metastatic colonization', is inefficient for many cancer types and is accomplished only by a minority of cancer cells that reach distant sites. Prevalent target sites are characteristic of many tumour entities, suggesting that inadequate support by distant tissues contributes to the inefficiency of the metastatic process. Here we show that a small population of cancer stem cells is critical for metastatic colonization, that is, the initial expansion of cancer cells at the secondary site, and that stromal niche signals are crucial to this expansion process. We find that periostin (POSTN), a component of the extracellular matrix, is expressed by fibroblasts in the normal tissue and in the stroma of the primary tumour. Infiltrating tumour cells need to induce stromal POSTN expression in the secondary target organ (in this case lung) to initiate colonization. POSTN is required to allow cancer stem cell maintenance, and blocking its function prevents metastasis. POSTN recruits Wnt ligands and thereby increases Wnt signalling in cancer stem cells. We suggest that the education of stromal cells by infiltrating tumour cells is an important step in metastatic colonization and that preventing de novo niche formation may be a novel strategy for the treatment of metastatic disease.     

Nicotinic acetylcholine receptors in attention circuitry: the role of layer VI neurons of prefrontal cortex

Cholinergic modulation of prefrontal cortex is essential for attention. In essence, it focuses the mind on relevant, transient stimuli in support of goal-directed behavior. The excitation of prefrontal layer VI neurons through nicotinic acetylcholine receptors optimizes local and top-down control of attention. Layer VI of prefrontal cortex is the origin of a dense feedback projection to the thalamus and is one of only a handful of brain regions that express the α5 nicotinic receptor subunit, encoded by the gene chrna5. This accessory nicotinic receptor subunit alters the properties of high-affinity nicotinic receptors in layer VI pyramidal neurons in both development and adulthood. Studies investigating the consequences of genetic deletion of α5, as well as other disruptions to nicotinic receptors, find attention deficits together with altered cholinergic excitation of layer VI neurons and aberrant neuronal morphology. Nicotinic receptors in prefrontal layer VI neurons play an essential role in focusing attention under challenging circumstances. In this regard, they do not act in isolation, but rather in concert with cholinergic receptors in other parts of prefrontal circuitry. This review urges an intensification of focus on the cellular mechanisms and plasticity of prefrontal attention circuitry. Disruptions in attention are one of the greatest contributing factors to disease burden in psychiatric and neurological disorders, and enhancing attention may require different approaches in the normal and disordered prefrontal cortex.     

细胞壁:决定植物细胞命运的信使

以前认为植物细胞壁是些没有作用的空盒子，现在揭示出：它在植物发育过程中是决定细胞命运的有力信号机。自从17世纪英国科学家罗伯特·胡克（RobertHoorke）用早期的显微镜对植物进行了研究之后，就了解到植物细胞被僵硬的壁所包被。今天，任何一本生物学教科书的专业词汇，叙述细胞壁的经典的狭义作用时，都把它们描写成一种被动地包装着有活性的细胞生命物质的纤维素盒子。新的研究表明，细胞壁承担着决定植物细胞命运的活性作用。壁是一条长廊，包含有碳水化合物和蛋白质——但其本性仍然是个巨大的秘密——能和细胞内部及外部的其它…     

High levels of mitochondrial DNA deletions in substantia nigra neurons in aging and Parkinson disease

Here we show that in substantia nigra neurons from both aged controls and individuals with Parkinson disease, there is a high level of deleted mitochondrial DNA (mtDNA) (controls, 43.3% +/- 9.3%; individuals with Parkinson disease, 52.3% +/- 9.3%). These mtDNA mutations are somatic, with different clonally expanded deletions in individual cells, and high levels of these mutations are associated with respiratory chain deficiency. Our studies suggest that somatic mtDNA deletions are important in the selective neuronal loss observed in brain aging and in Parkinson disease.     

全球化,科学词汇和生物学的未来

1 Biology for the 21st Century In a recent article in the New York Times (3/23/05), reporting on yet another upset to received views of the ways in which cells make use of their DNA, a prominent geneticist is quoted as remarking, "biologists have gotten used to the unexpected." Indeed, they have, as indeed, they have had to. Over the last few years, our understanding of molecular and developmental genetics has mutated dramatically in response to ever more complex analyses of ever more abundant and more complex data.     

Post-breeding season movements of Columbia spotted frogs ( Rana luteiventris ) in northeastern Oregon

Movements of Columbia spotted frogs ( Rana luteiventris ) were determined after breeding to provide managers with information on habitat requirements. We radio-tagged 47 adults and observed movements occurring with 22 frogs. Eleven frogs remained in breeding ponds, and 11 moved to other ponds or river stretches during spring and summer 1998. Distances frogs traveled to other water bodies ranged from 15 to 560 m. Movements appeared to be influenced by availability of habitat and aquatic conditions. Eleven of 16 frogs located within 100 m of other permanent water sources moved, while no frogs at an isolated breeding pond moved. Frogs moved to river stretches in July where water temperatures averaged 5.6 ° C cooler than ponds. Knowledge of Columbia spotted frog movements and habitat use in summer enables land managers to make decisions on activities that affect aquatic sites, vegetation, and stream structures that may influence frog populations.     

The protein kinase Pstol1 from traditional rice confers tolerance of phosphorus deficiency

As an essential macroelement for all living cells, phosphorus is indispensable in agricultural production systems. Natural phosphorus reserves are limited, and it is therefore important to develop phosphorus-efficient crops. A major quantitative trait locus for phosphorus-deficiency tolerance, Pup1, was identified in the traditional aus-type rice variety Kasalath about a decade ago. However, its functional mechanism remained elusive until the locus was sequenced, showing the presence of a Pup1-specific protein kinase gene, which we have named phosphorus-starvation tolerance 1 (PSTOL1). This gene is absent from the rice reference genome and other phosphorus-starvation-intolerant modern varieties. Here we show that overexpression of PSTOL1 in such varieties significantly enhances grain yield in phosphorus-deficient soil. Further analyses show that PSTOL1 acts as an enhancer of early root growth, thereby enabling plants to acquire more phosphorus and other nutrients. The absence of PSTOL1 and other genes-for example, the submergence-tolerance gene SUB1A-from modern rice varieties underlines the importance of conserving and exploring traditional germplasm. Introgression of this quantitative trait locus into locally adapted rice varieties in Asia and Africa is expected to considerably enhance productivity under low phosphorus conditions.