Gradualismus und Punktualismus Komplementäre Modelle evolutiven Wandels

The models of punctuated and gradual evolution are put in a historical perspective and contrasted with each other. Mechanisms of saltational change are discussed. A synthesis of the two models might be achieved on the basis ofC. H. Waddington’s theory of developmental canalization as recently discussed byA. Hoffman.     

Modulation of actin mRNAs in cultured vascular cells by matrix components and TGF-β1

Summary Alpha-smooth muscle actin is currently considered a marker of smooth muscle cell differentiation. However, during various physiologic and pathologic conditions, it can be expressed, sometimes only transiently, in a variety of other cell types, such as cardiac and skeletal muscle cells, as well as in nonmuscle cells. In this report, the expression of actin mRNAs in cultured rat capillary endothelial cells (RFCs) and aortic smooth muscle cells (SMCs) has been studied by Northern hybridization in two-dimensional cultures seeded on individual extracellular matrix proteins and in three-dimensional type I collagen gels. In two-dimensional cultures, in addition to cytoplasmic actin mRNAs which are normally found in endothelial cell populations, RFCs expressed α-smooth muscle (SM) actin mRNA at low levels. α-SM actin mRNA expression is dramatically enhanced by TGF-β₁. In addition, double immunofluorescence staining with anti-vWF and anti-α-SM-1 (a monoclonal antibody to α-SM actin) shows that RFCs co-express the two proteins. In three dimensional cultures, RFCs still expressed vWF, but lost staining for α-SM actin, whereas α-SM actin mRNA became barely detectable. In contrast to two-dimensional cultures, the addition of TGF-β₁ to the culture media did not enhance α-SM actin mRNA in three-dimensional cultures, whereas it induced rapid capillary tube formation. Actin mRNA expression was modulated in SMCs by extracellular matrix components and TGF-β₁ with a pattern very different from that of RFCs. Namely, the comparison of RFCs with other cell types such as bovine aortic endothelial cells shows that co-expression of endothelial and smooth muscle cell markers is very unique to RFCs and occurs only in particular culture conditions. This could be related to the capacity of these microvascular endothelial cells to modulate their phenotype in physiologic and pathologic conditions, particularly during angiogenesis, and could reflect different embryologic origins for endothelial cell populations. Supported by a Post-Doctoral Fellowship from the Swiss National Science Foundation (OK) and grant HL-RO1-28373 (JAM) from the Department of Human Services, Public Health Service, Washington, D.C.     

Regulation of the 3 beta-hydroxysteroid dehydrogenase activity in tissue fragments and microsomes from human term placenta: kinetic analysis and inhibition by steroids

The effects of 50 microM of progesterone (P4), estradiol (E2), estrone (E1), estriol (E3), dehydroepiandrosterone (DHIA), androstenedione (delta 4) and testosterone (T) on the bioconversion of [3H]pregnenolone (6 nM) to [3H]P4 were investigated by incubating 200 mg of tissue fragments as well as equivalent aliquots of microsomes from human term placenta during 30 min. All the steroids assayed, except E3, significantly inhibited the [3H]P4 formation in a microsome incubation system with respect to the control assay (P less than 0.001). Conversely in a tissue incubation system. P4, E1 as well as E3 had no effect on [3H]pregnenolone bioconversion while E2 slightly decreased the [3H]P4 formation (P less than 0.05) compared with the control. A significant inhibition was observed in this system with the other steroids (P less than 0.001). To investigate these apparent different results of inhibition-noninhibition of the same steroids irrespective of the system of incubation used, the effects of P4, E2 and T on 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) activity were studied in tissue fragments and microsomes in kinetic terms. The results found indicate that these steroids inhibited in a competitive fashion the 3 beta-HSD activity in both systems. The different Ki values found in tissue fragments and microsomes respectively for P4 (1.8 microM vs 0.5 microM), E2 (2.3 microM vs 0.6 microM) and T (0.25 microM vs 0.3 microM) explain the bioconversion results obtained in presence of 50 microM of the same steroids. These results include inhibition of [3H]P4 formation by T in tissue fragments as well as in microsomes whereas P4 and E2 inhibited the [3H]P4 formation only in microsomes. Furthermore, the comparison of these Ki values with the available data of intraplacental and circulating concentrations of the same steroids in human term pregnancy suggest that only P4 would be expected to cause marked 3 beta-HSD inhibition in physiological conditions.     

Bacterial host specificity of Lucinacea endosymbionts: Interspecific variation in 16S rRNA sequences

Abstract Three tropical lucinid clams ( Codakia orbiculata, Codakia pectinella and Lucina nassula ) from a shallow coastal environment have been studied regarding to their thioautotrophic bacterial endosymbionts. The 16S rRNA genes (rDNA) from these three endosymbionts were amplified using PCR. Phylogenetic analysis by distance matrix and parsimony methods always placed the newly examined symbionts within the monophyletic group composed of symbionts of the bivalve superfamily Lucinacea. A same single 16S rRNA sequence was found in C. orbiculata and C. pectinella and was identical to that found in C. orbicularis and Linga pensylvanica , two other lucinids living in the same type of environment. These data indicate that a same symbiont species may be associated with different host species. Lucina nassula hosts a symbiont with a distinct 16S rDNA sequence, but very closely related to the former.     

Use of Genetic and Physical Mapping to Locate the Spinal Muscular Atrophy Locus between Two New Highly Polymorphic DNA Markers

The gene for autosomal recessive forms of spinal muscular atrophy (SMA) has recently been mapped to chromosome 5ql3, within a 4-cM region between the blocks D5S465/D5S125 and MAP-1B/D5S112. We identified two new highly polymorphic microsatellite DNA markers—namely, AFM265wf5 (D5S629) and AFM281yh9 (D5S637)—which are the closest markers to the SMA locus. Multilocus analysis by the location-score method was used to establish the best estimate of the SMA gene location. Our data suggest that the most likely location for SMA is between locus D5S629 and the block D5S637/D5S351/MAP-1B/D5S112/D5S357. Genetic analysis of inbred SMA families, based on homozygosity by descent and physical mapping using mega-YACs, gave additional information for the loci order as follows: cen–D5S6–D5S125/D5S465–D5S435–D5S629–SMA–D5S637–D5S351–MAP–1B/D5S112–D5S357–D5S39–tel. These data give the direction for bidirectional walking in order to clone this interval and isolate the SMA gene.     

Selectively 13C-enriched DNA: 13C and 1H assignments of a triple helix by two-dimensional relayed HMQC experiments

Summary We present NMR studies of an intramolecular triple helix, the three strands of which have been linked by a hexaethylene glycol chain. To overcome the generally encountered difficulties of assignment in the homopyrimidine strands, the carbon C1 of the pyrimidines were selectively ¹³C-enriched. Assignments of the aromatic and sugar protons were obtained from NOESY-HMQC and TOCSY-HMQC spectra. We show that the recognition of a DNA duplex by a third strand via triplex formation is easily carried out in solution by observing the changes of the ¹H1–¹³C1 connectivities as a function of pH. Furthermore, the conformation of the sugars has been found to be C2-endo, on the basis of the coupling constant values directly measured in an HSQC spectrum.     

Les néoplasies intra-épithéliales du pénis: clinique,histologie et virologie

Analysis of 92 clinically dysplasic penile lesions revealed the presence of atypical mitoses and/or abnormalities of the basement membrane, definitive of intra-epithelial penile neoplasia, in 90% of cases. In 18.3% of patients (mean age 31 years) there was a genital human papillomavirus (HPV) infection. Histological lesions were low grade (State I) in 64% of cases, and high grade (Stages II or III) in 33% of cases, of which 4% were carcinoma in situ. HPV oncogene sequences were detected by Southern blotting in 75% and 95% of low and high grade lesions respectively, including 100% of carcinomas in situ. Patients with Stage II and III lesions were 7 to 10 years older than those with Stage I lesions, although circumcised men showed significantly fewer lesions than non-circumcised men, a difference not seen for the presence of genital HPV infection. The good correlation between morphological, histological and virological features allows screening for and early treatment of penile dysplasias.