Intraspecific polymorphism to interspecific divergence: genetics of pigmentation in Drosophila.

Genetic changes contributing to phenotypic differences within or between species have been identified for a handful of traits, but the relationship between alleles underlying intraspecific polymorphism and interspecific divergence is largely unknown. We found that noncoding changes in the tan gene, as well as changes linked to the ebony gene, contribute to pigmentation divergence between closely related Drosophila species. Moreover, we found that alleles linked to tan and ebony fixed in one Drosophila species also contribute to variation within another species, and that multiple genotypes underlie similar phenotypes even within the same population. These alleles appear to predate speciation, which suggests that standing genetic variation present in the common ancestor gave rise to both intraspecific polymorphism and interspecific divergence.

Independent effects of cis- and trans-regulatory variation on gene expression in Drosophila melanogaster.

Biochemical interactions between cis-regulatory DNA sequences and trans-regulatory gene products suggest that cis- and trans-acting polymorphisms may interact genetically. Here we present a strategy to test this hypothesis by comparing the relative cis-regulatory activity of two alleles in different genetic backgrounds. Of the eight genes surveyed in this study, five were affected by trans-acting variation that altered total transcript levels, two of which were also affected by differences in cis-regulation. The presence of trans-acting variation had no effect on relative cis-regulatory activity, showing that cis-regulatory polymorphisms can function independently of trans-regulatory variation. The frequency of such independent interactions on a genomic scale is yet to be determined.

Regulatory changes underlying expression differences within and between Drosophila species.

Differences in gene expression are an important source of phenotypic variation, and can be caused by changes in cis and/or trans regulation. cis-regulatory variants alter allele-specific expression, whereas trans-regulatory variants influence expression of both alleles in a diploid cell. Because of this difference, we hypothesize that natural selection may favor one type of change over the other. Here, we investigate contributions of cis- and trans-regulatory changes to variable intra- and interspecific gene expression using four strains of Drosophila melanogaster, three strains of D. simulans and a total of 78 genes. We show that cis-regulatory changes account for a greater proportion of the expression differences observed between rather than within species. These data are inconsistent with a neutral model assuming equal probabilities of fixation for cis- and trans-regulatory polymorphisms, suggesting that natural selection influences the molecular mechanisms underlying divergent gene expression. Specifically, cis-regulatory changes seem to accumulate preferentially over time.

Parent-of-origin effects on mRNA expression in Drosophila melanogaster not caused by genomic imprinting.

Parent-of-origin effects create differences in gene expression among genetically identical individuals. Using measurements of allele-specific expression, we demonstrate that previously reported parent-of-origin effects on standing mRNA levels in Drosophila melanogaster are not attributable to genomic imprinting. Offspring from reciprocal crosses exhibit differences in total expression without differences in allelic expression, indicating that other types of maternal and/or paternal effects alter expression.

Evolutionary changes in cis and trans gene regulation.

Differences in gene expression are central to evolution. Such differences can arise from cis-regulatory changes that affect transcription initiation, transcription rate and/or transcript stability in an allele-specific manner, or from trans-regulatory changes that modify the activity or expression of factors that interact with cis-regulatory sequences. Both cis- and trans-regulatory changes contribute to divergent gene expression, but their respective contributions remain largely unknown. Here we examine the distribution of cis- and trans-regulatory changes underlying expression differences between closely related Drosophila species, D. melanogaster and D. simulans, and show functional cis-regulatory differences by comparing the relative abundance of species-specific transcripts in F1 hybrids. Differences in trans-regulatory activity were inferred by comparing the ratio of allelic expression in hybrids with the ratio of gene expression between species. Of 29 genes with interspecific expression differences, 28 had differences in cis-regulation, and these changes were sufficient to explain expression divergence for about half of the genes. Trans-regulatory differences affected 55% (16 of 29) of genes, and were always accompanied by cis-regulatory changes. These data indicate that interspecific expression differences are not caused by select trans-regulatory changes with widespread effects, but rather by many cis-acting changes spread throughout the genome.

Temperature-controlled 830-nm low-level laser therapy of experimental pressure ulcers.

OBJECTIVE: This study was performed to evaluate the effectiveness of near-infrared low-level laser therapy (LLLT) treatment of pressure ulcers under temperature-controlled conditions. BACKGROUND DATA: Little information is available regarding the potential thermal effects of near-infrared photo-radiation during LLLT. METHODS: Pressure ulcers were created in C57BL mice by placing the dorsal skin between two round ceramic magnetic plates (12.0 x 5.0 mm, 2.4 g, 1 K Gauss) for three 12-h cycles. Animals were divided into three groups (n = 9) for daily light therapy (830 nm, CW, 5.0 J/cm(2)) on days 3-13 post ulceration in both groups A and B. A special heat-exchange device was applied in Group B to maintain a constant temperature at the skin surface (30 degrees C). Group C served as controls, with irradiation at 5.0 J/cm(2) using an incandescent light source. Temperature of the skin surface, and temperature alterations during treatment were monitored. The wound area was measured and the rate and time to complete healing were noted. RESULTS: The maximum temperature change during therapy was 2.0 +/- 0.64 degrees C in Group A, 0.2 +/- 0.2 degrees C in Group B and 3.54 degrees C +/- 0.72 in Group C. Complete wound closure occurred at 18 +/- 4 days in Groups A and B and 25 +/- 6 days in Group C (p