Determining the site of brain tumors; the use of radioactive iodine and phosphorus

By tests using radioactive iodine combined with diiodofluorescein, the site of tumors was correctly determined in 61 per cent of 39 cases of tumors of the cerebral hemispheres. In 19 cases where the focal radioactivity was increased 24 per cent or more over that of the surrounding area, there were no errors in localization. Fifteen patients with expanding intracranial lesions were tested at operation with radioactive phosphorus and 14 lesions were correctly localized. This procedure in which the needle probe was used was found of great value in rapidly locating and outlining the area of involvement.     

Transfer of exogenous glycosylphos-phatidylinositol (GPI)-linked molecules to plasma membranes

Purified GPI-linked molecules incorporate spontaneously in vitro into mammalian cell plasma membranes. Recent evidence suggests that the transferred molecules insert stably into the external leaflet of the acceptor cell plasma membrane through their acyl chains and behave subsequently in a way similar to endogenous GPI-linked molecules. Transfer of GPI-linked proteins between cells has also been documented in vivo and may explain the uptake by host cells o f pathogen-derived virulence factors carrying a GPI anchor. In this comment article, Subburaj Ilangumaran, Peter Robinson and Daniel Hoessli review what is known about GPI transfer and discuss the use of GPI transfer for transient cell-surface expression of foreign proteins.     

Transgenic white clover. Studies with the auxin-responsive promoter,GH3, in root gravitropism and lateral root development

We report an improved method for white clover (Trifolium repens) transformation usingAgrobacterium tumefaciens. High efficiencies of transgenic plant production were achieved using cotyledons of imbibed mature seed. Transgenic plants were recovered routinely from over 50% of treated cotyledons. Thebar gene and phosphinothricin selection was shown to be a more effective selection system thannptII (kanamycin selection) oraadA (spectinomycin selection). White clover was transformed with the soybean auxin responsive promoter, GH3, fused to the GUS gene (-glucuronidase) to study the involvement of auxin in root development. Analysis of 12 independent transgenic plants showed that the location and pattern of GUS expression was consistent but the levels of expression varied. The level of GH3:GUS expression in untreated plants was enhanced specifically by auxin-treatment but the pattern of expression was not altered. Expression of the GH3:GUS fusion was not enhanced by other phytohormones. A consistent GUS expression pattern was evident in untreated plants presumably in response to endogenous auxin or to differences in auxin sensitivity in various clover tissues. In untreated plants, the pattern of GH3:GUS expression was consistent with physiological responses which are regarded as being auxin-mediated. For the first time it is shown that localised spots of GH3:GUS activity occurred in root cortical tissue opposite the sites where lateral roots subsequently were initiated. Newly formed lateral roots grew towards and through these islands of GH3:GUS expression, implying the importance of auxin in controlling lateral root development. Similarly, it is demonstrated for the first time that gravistimulated roots developed a rapid (within 1 h) induction of GH3:GUS activity in tissues on the non-elongating side of the responding root and this induction occurred concurrently with root curvature. These transgenic plants could be useful tools in determining the physiological and biochemical changes that occur during auxin-mediated responses.     

The relationships among adhesion, stratification and differentiation in keratinocytes

Epidermis is a self-renewing, multilayered tissue composed primarily of keratinocytes. The epidermal keratinocyte follows a terminal differentiation pathway that under normal circumstances is tightly linked to its position within the epidermis and culminates in the formation of the protective barrier (stratum corneum) that constitutes the outermost layer of skin. Strong but pliant adhesive mechanisms are essential for normal functioning of the epidermis. In the epidermis, adhesion is mediated primarily by four structures: hemidesmosomes and focal adhesions, which function in cell-matrix adhesion, and desmosomes and adherens junctions, which function in cell-cell adhesion. In this review we concentrate on the transmembrane components of these structures, which are thought to mediate directly the adhesive function. Members of the integrin family of adhesion molecules comprise the transmembrane components of hemidesmosomes and focal adhesions, although hemidesmosomes also have a second, unrelated transmembrane molecule known as 'bullous pemphigoid antigen 2'. Members of the cadherin family are the transmembrane constituents of desmosomes and adherens junctions. Desmosomes consistently contain two types of cadherins (desmoglein and desmocollin), while adherens junctions may contain only one type of cadherin (E- or P-cadherin). Expression of most of the transmembrane components varies with the position of the keratinocyte within the epidermis and thus may reflect the degree of epidermal differentiation. All of the integrin subunits have been localized predominantly to the basal layer. In contrast, the cadherins show very complex expression patterns throughout the epidermis. Desmogleins and desmocollins (the desmosomal cadherins) are each encoded by three genes, and the expression of each gene is limited to certain epidermal layers. With respect to the cadherins of the adherens junction, it has been shown that E-cadherin is present throughout the epidermis, while P-cadherin is limited to the basal layer. Interestingly, these complex expression patterns of integrins and cadherins within the epidermis may not simply be passive events in differentiation; rather, evidence is accumulating that adhesion molecules can exert a dynamic role in epidermal differentiation/stratification. For example, decreased adhesion to extracellular matrix, induced by changes in one or more integrins, appears to be a signal that induces certain differentiation-related events. Even more profound effects on epidermal morphogenesis have been demonstrated for the cadherins. E- and/or P-cadherin is required not only to initiate normal intercellular junction formation but also for the subsequent development of a stratified epithelium. Thus, the findings to date with both integrins and cadherins suggest that adhesion molecules may function not just as direct mediators of adhesion, but also as regulators of epidermal stratification, differentiation, and morphogenesis.     

Digestion of haemoglobin by schistosomes: 35 years on

Adult schistosomes obtain nutrients by digesting haemoglobin, which they obtain from ingested host red blood cells. Here John Dalton, Angela Smith, Karen Clough and Paul Brindley argue that a cathepsin L proteinase recently identified in their laboratory as the predominant cysteine proteinase activity of Schistosoma mansoni may play the leading role in haemoglobin digestion. They discuss the importance of elucidating the roles of both cathepsin B and cathepsin L in the digestion of haemoglobin, since both should be considered important targets to which novel schistosomicidal agents could be directed.     

Fermentation of 6-Deoxyhexoses by Bacillus macerans

Under anaerobic conditions Bacillus macerans ATCC 7068 fermented 6-deoxyhexoses (l-rhamnose, l-fucose, and d-fucose) to a mixture of 1,2-propanediol (PD), acetone, H(2), CO(2), and ethanol. The final PD concentration was proportional to the amount of l-rhamnose fermented ( approximately 0.9 mol of PD per mol of rhamnose). PD was not produced from hexoses (e.g., d-glucose or l-mannose), despite active fermentation of these substrates. Relative to the fermentation of d-glucose, the fermentation of l-rhamnose was accompanied by a twofold reduction in yield of H(2), CO(2), and cell mass. Exposure of cell extracts to l-rhamnose resulted in the transient appearance of an aldehyde intermediate. Cell extracts contained a pyridine nucleotide-linked lactaldehyde reductase activity which converted synthetic d- or l-lactaldehyde to PD. The data suggest an Embden-Meyerhof pathway for 6-deoxyhexose catabolism, with the formation of lactaldehyde by a conventional aldolase cleavage reaction and subsequent reduction to PD.