Patterns of brain angiogenesis after vascular endothelial growth factor administration in vitro and in vivo

Vascular endothelial growth factor (VEGF) is a secreted endothelial cell mitogen that has been shown to induce vasculogenesis and angiogenesis in many organ systems and tumors. Considering the importance of VEGF to embryonic vascularization and survival, the effects of administered VEGF on developing or adult cerebrovasculature are unknown: can VEGF alter brain angiogenesis or mature cerebrovascular patterns? To examine these questions we exposed fetal, newborn, and adult rat cortical slice explants to graduated doses of recombinant VEGF. The effects of another known angiogenic factor, basic fibroblast growth factor (bFGF), were evaluated in a comparable manner. In addition, we infused VEGF via minipump into the adult cortex. Significant angiogenic effects were found in all VEGF experiments in a dose-responsive manner that were abolished by the addition of VEGF neutralizing antibody. Fetal and newborn explants had a highly complex network of branched vessels that immunoexpressed the flt-1 VEGF receptor, and flk-1 VEGF receptor expression was determined by reverse transcription–PCR. Adult explants had enlarged, dilated vessels that appeared to be an expansion of the existing network. All bFGF-treated explants had substantially fewer vascular profiles. VEGF infusions produced both a remarkable localized neovascularization and, unexpectedly, the expression of flt-1 on reactive astrocytes but not on endothelial cells. The preponderance of neovascularization in vitro and in vivo, however, lacked the blood–brain barrier (BBB) phenotype marker, GLUT-1, suggesting that in brain the angiogenic role of VEGF may differ from a potential BBB functional role, i.e., transport and permeability. VEGF may serve an important capacity in neovascularization or BBB alterations after brain injury.

Biogeographic range expansion into South America by Coccidioides immitis mirrors New World patterns of human migration

Long-distance population dispersal leaves its characteristic signature in genomes, namely, reduced diversity and increased linkage between genetic markers. This signature enables historical patterns of range expansion to be traced. Herein, we use microsatellite loci from the human pathogen Coccidioides immitis to show that genetic diversity in this fungus is geographically partitioned throughout North America. In contrast, analyses of South American C. immitis show that this population is genetically depauperate and was founded from a single North American population centered in Texas. Variances of allele distributions show that South American C. immitis have undergone rapid population growth, consistent with an epidemic increase in postcolonization population size. Herein, we estimate the introduction into South America to have occurred within the last 9,000–140,000 years. This range increase parallels that of Homo sapiens. Because of known associations between Amerindians and this fungus, we suggest that the colonization of South America by C. immitis represents a relatively recent and rapid codispersal of a host and its pathogen.

Star scientists and institutional transformation: Patterns of invention and innovation in the formation of the biotechnology industry

The most productive (“star”) bioscientists had intellectual human capital of extraordinary scientific and pecuniary value for some 10–15 years after Cohen and Boyer’s 1973 founding discovery for biotechnology [Cohen, S., Chang, A., Boyer, H. & Helling, R. (1973) Proc. Natl. Acad. Sci. USA 70, 3240–3244]. This extraordinary value was due to the union of still scarce knowledge of the new research techniques and genius and vision to apply them in novel, valuable ways. As in other sciences, star bioscientists were very protective of their techniques, ideas, and discoveries in the early years of the revolution, tending to collaborate more within their own institution, which slowed diffusion to other scientists. Close, bench-level working ties between stars and firm scientists were needed to accomplish commercialization of the breakthroughs. Where and when star scientists were actively producing publications is a key predictor of where and when commercial firms began to use biotechnology. The extent of collaboration by a firm’s scientists with stars is a powerful predictor of its success: for an average firm, 5 articles coauthored by an academic star and the firm’s scientists result in about 5 more products in development, 3.5 more products on the market, and 860 more employees. Articles by stars collaborating with or employed by firms have significantly higher rates of citation than other articles by the same or other stars. The U.S. scientific and economic infrastructure has been particularly effective in fostering and commercializing the bioscientific revolution. These results let us see the process by which scientific breakthroughs become economic growth and consider implications for policy.

Patterns of variance in stage-structured populations: Evolutionary predictions and ecological implications

Variability in population growth rate is thought to have negative consequences for organism fitness. Theory for matrix population models predicts that variance in population growth rate should be the sum of the variance in each matrix entry times the squared sensitivity term for that matrix entry. I analyzed the stage-specific demography of 30 field populations from 17 published studies for pattern between the variance of a demographic term and its contribution to population growth. There were no instances in which a matrix entry both was highly variable and had a large effect on population growth rate; instead, correlations between estimates of temporal variance in a term and contribution to population growth (sensitivity or elasticity) were overwhelmingly negative. In addition, survivorship or growth sensitivities or elasticities always exceeded those of fecundity, implying that the former two terms always contributed more to population growth rate. These results suggest that variable life history stages tend to contribute relatively little to population growth rates because natural selection may alter life histories to minimize stages with both high sensitivity and high variation.

Aluminum-Resistant Arabidopsis Mutants That Exhibit Altered Patterns of Aluminum Accumulation and Organic Acid Release from Roots1

Al-resistant (alr) mutants of Arabidopsis thaliana were isolated and characterized to gain a better understanding of the genetic and physiological mechanisms of Al resistance. alr mutants were identified on the basis of enhanced root growth in the presence of levels of Al that strongly inhibited root growth in wild-type seedlings. Genetic analysis of the alr mutants showed that Al resistance was semidominant, and chromosome mapping of the mutants with microsatellite and random amplified polymorphic DNA markers indicated that the mutants mapped to two sites in the Arabidopsis genome: one locus on chromosome 1 (alr-108, alr-128, alr-131, and alr-139) and another on chromosome 4 (alr-104). Al accumulation in roots of mutant seedlings was studied by staining with the fluorescent Al-indicator dye morin and quantified via inductively coupled argon plasma mass spectrometry. It was found that the alr mutants accumulated lower levels of Al in the root tips compared with wild type. The possibility that the mutants released Al-chelating organic acids was examined. The mutants that mapped together on chromosome 1 released greater amounts of citrate or malate (as well as pyruvate) compared with wild type, suggesting that Al exclusion from roots of these alr mutants results from enhanced organic acid exudation. Roots of alr-104, on the other hand, did not exhibit increased release of malate or citrate, but did alkalinize the rhizosphere to a greater extent than wild-type roots. A detailed examination of Al resistance in this mutant is described in an accompanying paper (J. Degenhardt, P.B. Larsen, S.H. Howell, L.V. Kochian [1998] Plant Physiol 117: 19–27).

A 20-nucleotide element in the intestinal fatty acid binding protein gene modulates its cell lineage-specific, differentiation-dependent, and cephalocaudal patterns of expression in transgenic mice.

A sequence of epithelial cell proliferation, allocation to four principal lineages, migration-associated differentiation, and cell loss occurs along the crypt-villus axis of the mouse intestine. The sequence is completed in a few days and is recapitulated throughout the life-span of the animal. We have used an intestine-specific fatty acid binding protein gene, Fabpi, as a model for studying regulation of gene expression in this unique developmental system. Promoter mapping studies in transgenic mice identified a 20-bp cis-acting element (5'-AGGTGGAAGCCATCACACTT-3') that binds small intestinal nuclear proteins and participates in the control of Fabpi's cephalocaudal, differentiation-dependent, and cell lineage-specific patterns of expression. Immunocytochemical studies using confocal and electron microscopy indicate that it does so by acting as a suppressor of gene expression in the distal small intestine/colon, as a suppressor of gene activation in proliferating and nonproliferating cells located in the crypts of Lieberkühn, and as a suppressor of expression in the growth factor and defensin-producing Paneth cell lineage. The 20-bp domain has no obvious sequence similarities to known transcription factor binding sites. The three functions modulated by this compact element represent the types of functions required to establish and maintain the intestine's remarkably complex spatial patterns of gene expression. The transgenes described in this report also appear to be useful in characterizing the crypt's stem cell hierarchy.