The ontogenetic complexity of developmental constraints

Developmental constraint is a theoretically important construct bridging ontogenetic and evolutionary studies. We propose a new operationalization of this notion that exploits the unusually rich measurement structure of landmark data. We represent landmark configurations by their partial warps, a basis for morphospace that represents a set of localized features of form. A finding of developmental constraint arises from the interplay between age-varying means and age-specific variances in these subspaces of morphospace. Examination of variances and means in 16 ventral skull landmarks in the cotton rat S. fulviventer at ages 1, 10, 20, and 30 days yielded three types of developmental constraint: canalization (constraint to relatively constant form age by age); chreods (reduction of variance orthogonal to the mean trajectory over ages); and opposition (reduction of age-specific variance along the mean trajectory over ages). While canalization and chreodic constraints have been noted previously, the oppositional type of constraint appears novel. Only one of our characters, relative length and orientation of the incisive foramen, appears to be canalized. Although skull growth becomes increasingly integrated through ontogeny, our characters display a remarkable spatiotemporal complexity in patterns of variance reduction. The specific assortment of constraints observed may be related to the precociality of Sigmodon. We suggest that Waddington's diagrammatic presentation of the “epigenetic landscape” may be misleading in quantitative studies of developmental regulation.     

Temperature coefficients of peptides dissolved in hexafluoroisopropanol monitor distortions of helices

Temperature coefficients are widely used as an indication of solvent accessibility to amide protons. Low temperature coefficients are related to low accessibility and are often interpreted as evidence for intramolecular hydrogen bonding. Conformational shifts, i.e. the difference between chemical shifts of a particular residue in a structured and in a random-coil conformation, provide information on secondary structure. In particular, negative CH conformational shifts are often used to delineate the extent of helical stretches. NH conformational shifts show large oscillations within a helix that have been interpreted as the result of helix distortions affecting hydrogen bond lengths. In the course of the study of different peptides that adopt a helical structure in the presence of the structure-inducing solvent hexafluoroisopropanol (HFIP), we have found a strong correlation between temperature coefficients and amide conformational shifts. However, contrary to the initial expectations, lower temperature coefficients were associated to amide protons involved in longer, and presumably weaker, hydrogen bonds. The correlation can be explained, however, assuming that, in helical peptides dissolved in HFIP, temperature affects the chemical shift of amide protons mainly by changing the average length of intramolecular hydrogen bonds and changes in solvent accessibility play only a secondary role under these experimental conditions. The pattern of temperature coefficients in helical peptides can therefore be used to identify short or long hydrogen bonds causing bending of the helix axis.     

Regulation of inositol monophosphatase in Saccharomyces cerevisiae

Inositol monophosphatase is a key enzyme in the de novo biosynthesis of inositol and in the phosphoinositide second-messenger signalling pathway. Inhibition of this enzyme is a proposed mechanism for lithium's pharmacological action in bipolar illness (manic depression). Very little is known about how expression of this enzyme is regulated. Because the yeast Saccharomyces cerevisiae has been shown to be an excellent model system in which to understand the regulation of inositol metabolism, we characterized inositol monophosphatase in this yeast. Lithium inhibited monophosphatase activity in vitro . Growth in the presence of inositol resulted in increased expression of the enzyme in vivo , although inositol had no effect on enzyme activity in vitro . The inositol effect was apparent when cells were grown in glucose but not in glycerol/ethanol. Monophosphatase activity was derepressed as cells entered stationary phase. This effect was apparent only during growth in glucose plus inositol. The results demonstrate that S. cerevisiae monophosphatase is inhibited by lithium and regulated by factors affecting phospholipid biosynthesis.     

Cloning and characterization of a gene from Pasteurella haemolytica A1 involved in lipopolysaccharide biosynthesis

Abstract A Pasteurella haemolytica A1 gene involved in the biosynthesis of a moiety on the core of the lipopolysaccharide molecule has been cloned and characterized. Escherichia coli clones which carry this gene showed an alteration of its lipopolysaccharide migration profile on tricine SDS-PAGE and exhibited resistance to the core-specific phage U3. In addition, lipopolysaccharide extracted from the E. coli clones was recognized by an anti-corespecific antiserum, but not by antiserum specific for the O antigen of P. haemolytica A1 lipopolysaccharide. Nucleotide sequence analysis of the cloned DNA identified an open reading frame ( lpsA ) coding for a protein of 263 amino acids which showed significant homology with a Haemophilus influenzae type b lipooligosaccharide biosynthesis gene. PCR amplification of genomic DNA, using primers based on the P. haemolytica A1 lpsA sequence, yielded products from only the A biotypes of P. haemolytica .     

Analysis of viability and cell types of macroalgal protoplasts using flow cytometry

The ability to rapidly distinguish viable sub-populations of cells within populations of macroalgal protoplast isolations was demonstrated using flow cytometry. Viable protoplasts from Ulva sp. and Porphyra perforata J. Ag. were distinguished from non-viable protoplasts based on differential fluorescein accumulation. The identities of cortical and epidermal protoplasts from Macrocystis pyrifera (L.) C. Ag. were inferred based on light-scattering and chlorophyll a autofluorescence. Three cell types could be distinguished among protoplasts released from thalli of P. perforata based on chlorophyll a and phycoerythrin autofluorescence. Mixed protoplast populations of Ulva sp. and P. perforata were also discernable based on relative chlorophyll a and phycoerythrin autofluorescence. The ability to screen heterogenous protoplast populations rapidly, combined with the cell sorting capabilities of many flow cytometers, should prove valuable for seaweed biotechnology.     

The maintenance ofBdellovibrio at low prey density

A mathematical model for the interaction ofBdellovibrio and its prey predicted that a relatively high prey density (7×10⁵ cells ml^–1) would be required for the establishment of an equilibrium in a mixed population [8]. The present report shows thatBdellovibrio can be maintained in a continuous culture when the prey cell density is much lower (2–5×10⁴ cells ml^–1), and closer to that of naturally occurring bacterial populations in sea waters.