Glutathione and Gts1p drive beneficial variability in the cadmium resistances of individual yeast cells

Phenotypic heterogeneity among individual cells within isogenic populations is widely documented, but its consequences are not well understood. Here, cell-to-cell variation in the stress resistance of Saccharomyces cerevisiae, particularly to cadmium, was revealed to depend on the antioxidant glutathione. Heterogeneity was decreased strikingly in gsh1 mutants. Furthermore, cells sorted according to differing reduced-glutathione (GSH) contents exhibited differing stress resistances. The vacuolar GSH-conjugate pathway of detoxification was implicated in heterogeneous Cd resistance. Metabolic oscillations (ultradian rhythms) in yeast are known to modulate single-cell redox and GSH status. Gts1p stabilizes these oscillations and was found to be required for heterogeneous Cd and hydrogen-peroxide resistance, through the same pathway as Gsh1p. Expression of GTS1 from a constitutive tet-regulated promoter suppressed oscillations and heterogeneity in GSH content, and resulted in decreased variation in stress resistance. This enabled manipulation of the degree of gene expression noise in cultures. It was shown that cells expressing Gts1p heterogeneously had a competitive advantage over more-homogeneous cell populations (with the same mean Gts1p expression), under continuous and fluctuating stress conditions. The results establish a novel molecular mechanism for single-cell heterogeneity, and demonstrate experimentally fitness advantages that depend on deterministic variation in gene expression within cell populations

Photoreceptor spectral sensitivities in terrestrial animals: adaptations for luminance and colour vision

This review outlines how eyes of terrestrial vertebrates and insects meet the competing requirements of coding both spatial and spectral information. There is no unique solution to this problem. Thus, mammals and honeybees use their long-wavelength receptors for both achromatic (luminance) and colour vision, whereas flies and birds probably use separate sets of photoreceptors for the two purposes. In particular, we look at spectral tuning and diversification among ‘long-wavelength’ receptors (sensitivity maxima at greater than 500 nm), which play a primary role in luminance vision. Data on spectral sensitivities and phylogeny of visual photopigments can be incorporated into theoretical models to suggest how eyes are adapted to coding natural stimuli. Models indicate, for example, that animal colour vision—involving five or fewer broadly tuned receptors—is well matched to most natural spectra. We can also predict that the particular objects of interest and signal-to-noise ratios will affect the optimal eye design. Nonetheless, it remains difficult to account for the adaptive significance of features such as co-expression of photopigments in single receptors, variation in spectral sensitivities of mammalian L-cone pigments and the diversification of long-wavelength receptors that has occurred in several terrestrial lineages

A preliminary note on banded karyotypes of the short-tailed shrew Blarina brevicauda (Mammalia, Insectivora)

Chromosomes of the short-tailed shrew Blarina brevicauda, which display the numerical polymorphism arisen from Robertsonian rearrangements, were analyzed with conventional and silver staining and G- and C-banding techniques. With respect to all specimens examined in the present study, the diploid chromosome number (2n) and fundamental autosomal arm number (FN) were 50 and 48, respectively. The karyotype consisted of 24 pairs of acrocentric autosomes, a large-sized metacentric X chromosome, and a small-sized submetacentric Y chromosome. The comparison with previous findings suggested the geographic polymorphism of Y chromosome in this species. All autosomes and the X chromosome carried slight centromeric constitutive heterochromatin, whereas the Y chromosome was entirely heterochromatic. On the satellites of short arms of two autosomal pairs, the nucleolus organizer regions (NORs) were recognized. The G- and C-banded and Ag-NOR-stained karyotypes presented in the present study could be useful cytogenetic characteristics for specification of chromosomes participating in Robertsonian rearrangements within this species and for karyo-systematic study of genus Blarina