Extraordinary levels of cadmium and zinc in a marine sponge,Tedania charcoti Topsent: inorganic chemical defense agents

The Antarctic marine spongeTedania charcoti has been shown to contain extraordinarily high natural concentrations of cadmium and zinc, which have in turn been correlated to the ability of the crude ethanol extract to modulate protein phosphorylation in chicken forebrain and to inhibit the growth of several test bacteria.     

The temporal requirement for endothelin receptor-B signalling during neural crest development

Endothelin receptor B (EDNRB) is a G-protein-coupled receptor with seven transmembrane domains which is required for the development of melanocytes and enteric neurons. Mice that are homozygous for a null mutation in the Ednrb gene are almost completely white and die as juveniles from megacolon. To determine when EDNRB signalling is required during embryogenesis, we have exploited the tetracycline-inducible system to generate strains of mice in which the endogenous Ednrb locus is under the control of the tetracycline-dependant transactivators tTa or rtTA. By using this system to express Ednrb at different stages of embryogenesis, we have determined that EDNRB is required during a restricted period of neural crest development between embryonic days 10 and 12.5. Moreover, our results imply that EDNRB is required for the migration of both melanoblasts and enteric neuroblasts.     

A telomerase component is defective in the human disease dyskeratosis congenita

The X-linked form of the human disease dyskeratosis congenita (DKC) is caused by mutations in the gene encoding dyskerin. Sufferers have defects in highly regenerative tissues such as skin and bone marrow, chromosome instability and a predisposition to develop certain types of malignancy. Dyskerin is a putative pseudouridine synthase, and it has been suggested that DKC may be caused by a defect in ribosomal RNA processing. Here we show that dyskerin is associated not only with H/ACA small nucleolar RNAs, but also with human telomerase RNA, which contains an H/ACA RNA motif. Telomerase adds simple sequence repeats to chromosome ends using an internal region of its RNA as a template, and is required for the indefinite proliferation of primary human cells. We find that primary fibroblasts and lymphoblasts from DKC-affected males are not detectably deficient in conventional H/ACA small nucleolar RNA accumulation or function; however, DKC cells have a lower level of telomerase RNA, produce lower levels of telomerase activity and have shorter telomeres than matched normal cells. The pathology of DKC is consistent with compromised telomerase function leading to a defect in telomere maintenance, which may limit the proliferative capacity of human somatic cells in epithelia and blood.     

Distribution of spatial and nonspatial information in dorsal hippocampus

The hippocampus in the mammalian brain is required for the encoding of current and the retention of past experience. Previous studies have shown that the hippocampus contains neurons that encode information required to perform spatial and nonspatial short-term memory tasks. A more detailed understanding of the functional anatomy of the hippocampus would provide important insight into how such encoding occurs. Here we show that hippocampal neurons in the rat are distributed anatomically in distinct segments along the length of the hippocampus. Each longitudinal segment contains clusters of neurons that become active when the animal performs a task with spatial attributes. Within these same segments are ordered arrangements of neurons that encode the nonspatial aspects of the task appropriate to those spatial features. Thus, anatomical segregation of spatial information, together with the interleaved representation of nonspatial information, represents a structural framework that may help to resolve conflicting views of hippocampal function.     

Periodicity in marine phosphorus burial rate

There have been arguments both for and against a periodicity of 26-33 million years (Myr) in terrestrial and extraterrestrial records. The best way to identify such periodicity is the analysis of geomarine evolutionary records. We have analysed the marine sedimentary phosphorus burial rate (PBR), as fluctuations in this rate are strong indicators of the coupling of climate, continental weathering and ocean primary productivity. We find a statistically significant harmonic component of 33 +/- 3 Myr against the estimated robust background noise spectrum, supporting the idea that geomarine processes are cyclic.     

Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2.     

A structural change in the kinesin motor protein that drives motility

Kinesin motors power many motile processes by converting ATP energy into unidirectional motion along microtubules. The force-generating and enzymatic properties of conventional kinesin have been extensively studied; however, the structural basis of movement is unknown. Here we have detected and visualized a large conformational change of an approximately 15-amino-acid region (the neck linker) in kinesin using electron paramagnetic resonance, fluorescence resonance energy transfer, pre-steady state kinetics and cryo-electron microscopy. This region becomes immobilized and extended towards the microtubule 'plus' end when kinesin binds microtubules and ATP, and reverts to a more mobile conformation when gamma-phosphate is released after nucleotide hydrolysis. This conformational change explains both the direction of kinesin motion and processive movement by the kinesin dimer.