Polycystins 1 and 2 mediate mechanosensation in the primary cilium of kidney cells

Several proteins implicated in the pathogenesis of polycystic kidney disease (PKD) localize to cilia. Furthermore, cilia are malformed in mice with PKD with mutations in TgN737Rpw (encoding polaris). It is not known, however, whether ciliary dysfunction occurs or is relevant to cyst formation in PKD. Here, we show that polycystin-1 (PC1) and polycystin-2 (PC2), proteins respectively encoded by Pkd1 and Pkd2, mouse orthologs of genes mutated in human autosomal dominant PKD, co-distribute in the primary cilia of kidney epithelium. Cells isolated from transgenic mice that lack functional PC1 formed cilia but did not increase Ca(2+) influx in response to physiological fluid flow. Blocking antibodies directed against PC2 similarly abolished the flow response in wild-type cells as did inhibitors of the ryanodine receptor, whereas inhibitors of G-proteins, phospholipase C and InsP(3) receptors had no effect. These data suggest that PC1 and PC2 contribute to fluid-flow sensation by the primary cilium in renal epithelium and that they both function in the same mechanotransduction pathway. Loss or dysfunction of PC1 or PC2 may therefore lead to PKD owing to the inability of cells to sense mechanical cues that normally regulate tissue morphogenesis.     

Three-dimensional structure of the ion-coupled transport protein NhaA

Ion-coupled membrane-transport proteins, or secondary transporters, comprise a diverse and abundant group of membrane proteins that are found in all organisms. These proteins facilitate solute accumulation and toxin removal against concentration gradients using energy supplied by ion gradients across membranes. NhaA is a Na+/H+ antiporter of relative molecular mass 42,000, which is found in the inner membrane of Escherichia coli, and which has been cloned and characterized. NhaA uses the H+ electrochemical gradient to expel Na+ from the cytoplasm, and functions primarily in the adaptation to high salinity at alkaline pH. Most secondary transporters, including NhaA, are predicted to have 12 transmembrane helices. Here we report the structure of NhaA, at 7 A resolution in the membrane plane and at 14 A vertical resolution, determined from two-dimensional crystals using electron cryo-microscopy. The three-dimensional map of NhaA reveals 12 tilted, bilayer-spanning helices. A roughly linear arrangement of six helices is adjacent to a compact bundle of six helices, with the density for one helix in the bundle not continuous through the membrane. The molecular organization of NhaA represents a new membrane-protein structural motif and offers the first insights into the architecture of an ion-coupled transport protein.     

Isotype exclusion and transgene down-regulation in immunoglobulin-lambda transgenic mice

A given B lymphocyte makes an antibody containing either kappa- or lambda-light chains, but not both. This isotype exclusion is effected at the level of the rearrangement of the immunoglobulin gene segments, although by an unknown mechanism. An attractive possibility is that, following productive rearrangement of one of the light-chain loci, the newly synthesized light-chain polypeptide inhibits DNA rearrangement for the other isotype. To test such feedback regulation, we have created transgenic mice carrying a rearranged lambda 1-gene. By contrast with the B cells in normal newborn mice which are mainly kappa+lambda-, the B cells in the newborn transgenic mice express lambda- but not kappa-chains. We propose that the synthesis of any light chain, be it kappa or lambda, that allows expression of IgM on the cell surface results in a cessation of all V-J joining. Interestingly, the limited light-chain repertoire of the transgenic mice does not persist and most adult B cells express endogenous kappa-rearrangements and down-regulate the transgene.     

A new anatomy of the prestalk zone in Dictyostelium

The characteristic structure of the mature Dictyostelium culminant is created by the regionalized cellular differentiation and directed movement of prestalk cells. The front prestalk zone of the migratory slug has previously been considered to be a homogeneous tissue. Here we demonstrate, however, the existence of multiple classes of prestalk cells located in different parts or the slug anterior. The pDd56 and pDd63 genes encoding closely related extracellular matrix proteins are dependent for their expression upon DIF-1, the specific stalk-cell inducer. We have fused the promoters of the two genes to a modified chloramphenicol acetyltransferase (cat) gene to produce immunologically detectable proteins which localize to the cell nucleus. These two markers define three distinct kinds of 'prestalk' cells. One class, which we term 'prestalk A' cells, expressed the pDd63 gene. 'Prestalk B' cells express pDd56 and may also express the pDd63 gene. A third class, which we term 'prestalk 0' cells, expresses neither marker.     

Modulation of single Ca2+-dependent K+-channel activity by protein phosphorylation

There is considerable evidence that cyclic AMP can modulate the electrical activity of excitable cells and that protein phosphorylation by the catalytic subunit (CS) of cAMP-dependent protein kinase is a necessary step in these modulatory effects. In analogy to alterations in enzyme activities following phosphorylation, it seems possible that direct phosphorylation of ion-channel proteins may alter their gating properties, giving rise to the observe changes in electrical activity. However, the results obtained so far do not indicate whether it is ion channels themselves that are phosphorylated, or whether phosphorylation is simply an early step in some cascade of events which leads ultimately to modulation of channel activity. The development of single-channel recording techniques has provided a way to investigate this question. Here we describe effects of CS on the activity of individual CA2+-dependent K+ channels from the nervous system of the land snail Helix measured in isolated membrane patches and in artificial phospholipid bilayers. The results demonstrate that cAMP-dependent protein phosphorylation produces long-lasting changes in the activity of individual channels, and indicate that the relevant phosphorylation site is closely associated with the channel.     

A point mutation in the neu oncogene mimics ligand induction of receptor aggregation

The rat neu gene, which encodes a protein closely related to the epidermal growth factor receptor, is a proto-oncogene that can be converted into an oncogene by a point mutation. Both genes encode proteins with a relative molecular mass of 185,000 but the question of why the neu gene product, p185neu, is oncogenic, whereas the product of c-neu, p185c-neu, is not, remains unanswered. The proteins have several features common to the family of tyrosine kinase growth-factor receptors, including cysteine-rich external domains, a hydrophobic transmembrane region and a cytoplasmic tyrosine kinase domain. The oncogenic p185neu differs from p185c-neu by an amino-acid substitution in the transmembrane region of the glycoprotein: this replacement of valine by glutamic acid at position 664 induces increased intrinsic tyrosine kinase activity which is associated with transformation. Many glycoproteins with charged amino acids in the transmembrane region exist as multimeric complexes at the plasma membrane. We have therefore investigated the association state of both products of the neu gene and show that the oncoprotein p185neu is organized at the plasma membrane primarily in an aggregated form, but that p185c-neu is not. Induction of an aggregated state may mimic aspects of ligand-induced receptor aggregation resulting in enzymatic activation that leads to cellular transformation.     

Distribution and first reports of Branchiobdellida (Annelida: Clitellata) on crayfish in the prairie provinces of Canada

Orconectes virilis (northern crayfish) were collected from 67 sites in Alberta, Saskatchewan, Manitoba, and far-western Ontario, Canada, and yielded 2 species of branchiobdellidans, Cambarincola vitreus and Cambarincola chirocephalus. This is the first report of branchiobdellidans in the Prairie Provinces. Cambarincola vitreus was distributed across the study area, but C. chirocephalus appeared to be restricted to southeastern Saskatchewan, southern Manitoba, and the site in western Ontario. Neither branchiobdellidan species was observed on crayfish in the Beaver River or the South Saskatchewan River and associated tributaries upstream (west) of Saskatoon, Saskatchewan, despite multiple sampling at these locations.     

Review

In this paper we study some methodological problems associated with the development of one of the major theories in low temperature physics, that of superconductivity. The first experimental results of 1911 were interpreted within a framework that hindered the paradoxical aspects of the new phenomenon. Various research programmes degenerated until new experimental results forced a reappraisal of the existing theoretical framework making possible a different formulation of the problem that had to be solved. This led to a progressive research programme, whose positive heuristic we also study.