Hervé Le Guyader

Confocal scanning optical microscopy and three-dimensional imaging

Summary— Confocal scanning optical microscopy has significant advantages over conventional fluorescence microscopy: it rejects the out‐of‐locus light and provides a greater resolution than the wide‐field microscope. In laser scanning optical microscopy, the specimen is scanned by a diffraction‐limited spot of laser light and the fluorescence emission (or the reflected light) is focused onto a photodetector. The imaged point is then digitized, stored into the memory of a computer and displayed at the appropriate spatial position on a graphic device as a part of a two‐dimensional image. Thus, confocal scanning optical microscopy allows accurate non‐invasive optical sectioning and further three‐dimensional reconstruction of biological specimens. Here we review the recent technological aspects of the principles and uses of the confocal microscope, and we introduce the different methods of three‐dimensional imaging.

Biochemical analysis of the interaction between elongation factor 1α and α/β‐tubulins from a ciliate, Tetrahymena pyriformis

The interaction between elongation factor 1α (EF‐1α) and α/β‐tubulins has been analyzed in vivo and in vitro. An association of both α‐ and β‐tubulins with EF‐1α in the lysate of Tetrahymena pyriformis was detected by co‐immunoprecipitation analysis. In contrast, in vitro biomolecular interaction analysis with glutathione S‐transferase (GST) fusion proteins revealed that GST‐β‐tubulin, but not GST‐α‐tubulin, can bind to GST‐EF‐1α. Two β‐tubulin binding sites have been identified to reside in the domains I and III of EF‐1α. In addition, β‐tubulin itself seems to have two distinct interaction sites for each of the domains. Since domain II of EF‐1α did not interact with β‐tubulin, we have re‐evaluated the phylogenetic status of ciliates using EF‐1α sequences devoid of domain II. The phylogenetic tree thus obtained was significantly different from that inferred from the whole sequence of EF‐1α, suggesting the presence of functional constraints on the molecular evolution of EF‐1α.

The neuronal zootype. An hypothesis.

We present an hypothesis, derived from the zootype concept of Slack, Holland and Graham. The main point of this hypothesis is to postulate that the primordial function of the zootype genes is to design an appropriate neuronal network in bilaterian animals, by controlling the genes involved in the specificity of the axon pathways. This would be the primary function of the zootype genes in development and their primitive function in evolution. The hypothesis is discussed in view of the current knowledge on the Hox genes, their evolution, their genomic organization, their expression and their targets.