New developments in developmental biology

A report on the 15th International Society of Developmental Biologists Congress, Sydney, Australia, 3-7 September 2005.     

Complete nucleotide sequences of bovine alpha S2- and beta-casein cDNAs: comparisons with related sequences in other species

The nucleotide sequences corresponding to bovine alpha S2- and beta- casein mRNAs have been determined by cDNA analysis. Both sequences appear to be complete at their 5' ends. The nucleotide sequence of alpha S2-casein, when compared with the corresponding cavine A sequence, helps to define the boundaries of a large amino acid repeat (approximately 80 residues) whereas comparisons with the nucleotide sequences of rat gamma- and mouse epsilon-casein mRNAs also reveal extensive sequence similarities. An alignment of these four sequences shows that the divergence of their translated regions has been characterized by the duplication and deletion of discrete segments of sequence that probably correspond to exons. A high degree of nucleotide substitution is also found when the four sequences are compared, except for well-conserved leader-peptide and phosphorylation-site sequences and, to a lesser extent, the 5'-untranslated regions. Similar comparison of the bovine and rat beta-caseins shows that their divergence has involved a high rate of nucleotide substitution but that no major insertions or deletions of sequence have occurred. The several splice sites that have veen defined in the rat beta-casein gene are likely to have been conserved in the bovine. The contrasting evolutionary histories of the alpha- and beta-casein coding sequences correlate with the distinctive functions of these proteins in the casein micelle system in milk.      

Aspergillus terreus and its toxic metabolites as a food contaminant in some Egyptian Bakery products and grains

A. terreus isolates isolated from some bakery products, corn and rice were found to be able to produce territrems. 90% of theA. terreus isolated from bakery products were able to produce territrem A, with a mean of 0.09 ppm, while 80% ofA. terreus isolates produce territrem B with a mean of 0.24 ppm. On the other hand 31.8% of the isolates ofA. terreus from corn were able to produce territrem A with a mean of 0.44 ppm. ConcerningA. terreus isolates from rice, 66.7% were found to produce territrem A, with a mean of 5.28 ppm, and 77.8% of the isolates produced territrem B with a mean of 1.79 ppm.     

Adaptive evolution of G-protein coupled receptor genes

The phylogeny and patterns of nucleotide substitutions in the visual pigment genes, adrenergic receptor genes, muscarinic receptor genes, and in the human mas oncogene were studied by comparing their DNA sequences. The evolutionary tree obtained shows that the visual pigment genes and mas oncogene form one cluster and that the receptor genes form another. In the evolution of rhodopsin genes, synonymous substitutions outnumber nonsynonymous substitutions. This is consistent with the neutral theory of molecular evolution. However, the early evolutionary stages of alpha- and beta-adrenergic and muscarinic receptors are notable for significantly more nonsynonymous substitutions than synonymous substitutions, suggesting the acquisition of novel functional adaptations. Variable rates of nonsynonymous changes in different domains of these proteins reveal DNA segments that might have been important in their functional adaptations.      

No evidence for learned mating discrimination in male Drosophila pseudoobscura

Background  

Since females often pay a higher cost for heterospecific matings, mate discrimination and species recognition are driven primarily by female choice. In contrast, frequent indiscriminate matings are hypothesized to maximize male fitness. However, recent studies show that previously indiscriminate males (e.g., Drosophila melanogaster and Poecilia reticulata) can learn to avoid heterospecific courtship. This ability of males to discriminate against heterospecific courtship may be advantageous in populations where two species co-occur if courtship or mating is costly.     

Functional and structural insight into properdin control of complement alternative pathway amplification

Properdin (FP) is an essential positive regulator of the complement alternative pathway (AP) providing stabilization of the C3 and C5 convertases, but its oligomeric nature challenges structural analysis. We describe here a novel FP deficiency (E244K) caused by a single point mutation which results in a very low level of AP activity. Recombinant FP E244K is monomeric, fails to support bacteriolysis, and binds weakly to C3 products. We compare this to a monomeric unit excised from oligomeric FP, which is also dysfunctional in bacteriolysis but binds the AP proconvertase, C3 convertase, C3 products and partially stabilizes the convertase. The crystal structure of such a FP-convertase complex suggests that the major contact between FP and the AP convertase is mediated by a single FP thrombospondin repeat and a small region in C3b. Small angle X-ray scattering indicates that FP E244K is trapped in a compact conformation preventing its oligomerization. Our studies demonstrate an essential role of FP oligomerization in vivo while our monomers enable detailed structural insight paving the way for novel modulators of complement.     

A dye-binding induced conformational transition of poly-(methacrylic acid) by Auramine O in aqueous solutions. I. Experimental results

Binding of auramine O to poly-(methacrylic acid) (PMA) has been established over a large range of C⁰_p/C⁰_d values using spectroscopic methods (UV absorption and visible fluorescence emission spectra), equilibrium and sedimentation dialysis, potentiometric and viscosimetric titrations. All the results show qualitative agreement with those obtained previously with the system crystal violet-PMA although the binding seems to be less strong for auramine O than for crystal violet. From dialysis experiments binding isotherms were obtained at three different degrees of neutralization α'; at α' = 0.10 the results could be fitted to a Langmuir isotherm but at α' equal to 0.40 and 0.65 deviations with respect to such an isotherm occur. The results of potentiometric and viscosimetric titrations confirm that the conformational transition which the dye-free PMA exhibits upon ionization is affected by the dye binding. The region in which the conformational transion occurs is broadened and is less sharply defined in the presence of auramine O.