Role of collagen and fibronectin in neural crest cell adhesion and migration

Cultured neural crest cells which are freshly trypsinized require serum or purified fibronectin to attach to collagen substrates of types I–V. Furthermore, neural crest cells migrate in a Boyden chamber in response to fibronectin, and a “checkerboard” analysis demonstrates that fibronectin is both chemotactic and chemokinetic for these cells. It is proposed that collagen serves as a substrate for neural crest cells as they migrate in the early embryo. By mediating the cells' attachment to collagen, fibronectin may influence the movement of the cells. Local differences in fibronectin concentration or availability in the matrix could affect the degree of attachment of the cells to the collagen substrate and could also direct their migration by serving as a chemoattractant.     

Organization of the Rosy Locus in DROSOPHILA MELANOGASTER: Further Evidence in Support of a CIS-Acting Control Element Adjacent to the Xanthine Dehydrogenase Structural Element

The present report summarizes our recent progress in the genetic dissection of an elementary genetic unit in a higher organism, the rosy locus (ry:3--52.0) in Drosophila melanogaster. Pursuing the hypothesis that the rosy locus includes a noncoding control region, as well as a structural element coding for the xanthine dehydrogenase (XDH) peptide, experiments are described that characterize and map a rosy locus variant associated with much lower than normal levels of XDH activity. Experiments are described that fail to relate this phenotype to alteration in the structure of the XDH peptide, but clearly associate this character with variation in number of molecules of XDH per fly. Large-scale fine-structure recombination experiments locate the genetic basis for this variation in the number of molecules of XDH per fly to a site immediately to the left of the XDH structural element within a region previously designated as the XDH control element. Moreover, experiments clearly separate this "underproducer" variant site from a previously described "overproducer" site within the control region. Examination of enzyme activity in electrophoretic gels of appropriate heterozygous genotypes demonstrates the cis-acting nature of this variation in the number of molecules of XDH. A revision of the map of the rosy locus, structural and control elements is presented in the light of the additional mapping data now available.     

Nitrate reductase activity and growth in Paul's Scarlet rose suspension cultures in relation to nitrogen source and molybdenum

Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO₃ ^- medium, activity in NO₃ ^--Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO₃ ^- alone was added to NO₃ ^- or urea+Mo cultures. In NO₃ ^--Mo cultures, Mo alone or with NO₃ ^- caused a similar increase in activity, whereas urea-Mo cultures required both NO₃ ^- and Mo for enzyme induction.Abbreviations FAD flavin adenine dinucleotide - Mo molybdenum - NADH reduced nicotinamide adenine dinucleotide - NO₃ ^-+Mo standard MX₁ culture medium - NO₃ ^--Mo MX₁ medium purified of Mo and used for continuous subculture with nitrate - NR nitrate reductase - PSR Paul's Scarlet rose - PVP polyvinylpyrrolidone - U urea - U+Mo MX₁ medium containing urea instead of nitrate - U-Mo MX₁ medium containing urea instead of nitrate and also purified of Mo     

Significance of dimers to the size of newly synthesized DNA in UV-irradiated Chinese hamster ovary cells.

DNA synthesized after UV irradiation is smaller than that in unirradiated cells even when pulse-labeling times are increased to compensate for the overall reduction in the rate of DNA replication. By isolating newly replicated DNA, incubating it with dimer-specific endonuclease from Micrococcus luteus, and analyzing it on alkaline sucrose gradients, we have been able to demonstrate that this DNA is synthesized in segments corresponding in size to the interdimer distance on the parental strand. In addition, the same DNA analyzed on neutral gradients shows no reduction in molecular weight as a result of UV irradiation and/or endonuclease digestion. Our data are thus inconsistent with the presence of "gaps" in newly synthesized DNA opposite the dimers on the parental strand. We suggest that if such gaps are produced as a result of delayed synthesis around dimers, they are filled before the growing point reaches the next dimer.     

Environmental history and physiological state influence feeding responses of Atrina zelandica to suspended sediment concentrations

Epifaunal suspension-feeding bivalves can play important roles in marine ecosystems affecting macrobenthic communities, benthic boundary layers and benthic-pelagic coupling, not just by their presence but also by any changes in feeding behaviour. While seston quality and quantity have consistently been found to be important influences on the feeding rates of suspension-feeding bivalves, factors stressing individuals are also likely to be important, as they may affect energy-dependent thresholds of response. We postulated that (1) history of seston quantity would affect how suspension feeders deal with increases in total suspended particulates, and (2) high-seston concentrations would affect feeding rates more in individuals whose energy reserves were low after spawning. Three sites were selected for short-term (1 day) feeding experiments on the pinnid bivalve, Atrina zelandica. At one site, the experiment was run pre-and postspawning. Atrina exhibited high rejection of filtered particles (mostly 75% to 100%) and high organic absorption efficiencies (0.9-1) at all seston levels. Strong differences in the response of feeding behaviour to increased seston concentrations were observed between A. zelandica from the different sites, with lesser differences observed between times. The site-specific feeding responses to seston concentrations observed are likely to affect our ability to model responses of A. zelandica to sediment loading and to influence the importance of A. zelandica to benthic-pelagic coupling.