Two Rapidly Evolving Genes Contribute to Male Fitness in Drosophila

Purifying selection often results in conservation of gene sequence and function. The most functionally conserved genes are also thought to be among the most biologically essential. These observations have led to the use of sequence conservation as a proxy for functional conservation. Here we describe two genes that are exceptions to this pattern. We show that lack of sequence conservation among orthologs of CG15460 and CG15323 – herein named jean-baptiste (jb) and karr respectively – does not necessarily predict lack of functional conservation. These two Drosophila melanogaster genes are among the most rapidly evolving protein-coding genes in this species, being nearly as diverged from their D. yakuba orthologs as random sequences are. jb and karr are both expressed at an elevated level in larval males and adult testes, but they are not accessory gland proteins and their loss does not affect male fertility. Instead, knockdown of these genes in D. melanogaster via RNA interference caused male-biased viability defects. These viability effects occur prior to the third instar for jb and during late pupation for karr. We show that putative orthologs to jb and karr are also expressed strongly in the testes of other Drosophila species and have similar gene structure across species despite low levels of sequence conservation. While standard molecular evolution tests could not reject neutrality, other data hint at a role for natural selection. Together these data provide a clear case where a lack of sequence conservation does not imply a lack of conservation of expression or function

Neonatal NMDA receptor blockade disrupts spike timing and glutamatergic synapses in fast spiking interneurons in a NMDA receptor hypofunction model of schizophrenia

The dysfunction of parvalbumin-positive, fast-spiking interneurons (FSI) is considered a primary contributor to the pathophysiology of schizophrenia (SZ), but deficits in FSI physiology have not been explicitly characterized. We show for the first time, that a widely-employed model of schizophrenia minimizes first spike latency and increases GluN2B-mediated current in neocortical FSIs. The reduction in FSI first-spike latency coincides with reduced expression of the Kv1.1 potassium channel subunit which provides a biophysical explanation for the abnormal spiking behavior. Similarly, the increase in NMDA current coincides with enhanced expression of the GluN2B NMDA receptor subunit, specifically in FSIs. In this study mice were treated with the NMDA receptor antagonist, MK-801, during the first week of life. During adolescence, we detected reduced spike latency and increased GluN2B-mediated NMDA current in FSIs, which suggests transient disruption of NMDA signaling during neonatal development exerts lasting changes in the cellular and synaptic physiology of neocortical FSIs. Overall, we propose these physiological disturbances represent a general impairment to the physiological maturation of FSIs which may contribute to schizophrenia-like behaviors produced by this model

Two-step Photoionization Of Potassium Atoms

The cross section for photoionization of potassium atoms in the 4P2 states has been measured in a triple-crossed-beam experiment. © 1978 The American Physical Society

Coordinated evolution of co-expressed gene clusters in the Drosophila transcriptome

Abstract Background Co-expression of genes that physically cluster together is a common characteristic of eukaryotic transcriptomes. This organization of transcriptomes suggests that coordinated evolution of gene expression for clustered genes may also be common. Clusters where expression evolution of each gene is not independent of their neighbors are important units for understanding transcriptome evolution. Results We used a common microarray platform to measure gene expression in seven closely related species in the Drosophila melanogaster subgroup, accounting for confounding effects of sequence divergence. To summarize the correlation structure among genes in a chromosomal region, we analyzed the fraction of variation along the first principal component of the correlation matrix. We analyzed the correlation for blocks of consecutive genes to assess patterns of correlation that may be manifest at different scales of coordinated expression. We find that expression of physically clustered genes does evolve in a coordinated manner in many locations throughout the genome. Our analysis shows that relatively few of these clusters are near heterochromatin regions and that these clusters tend to be over-dispersed relative to the rest of the genome. This suggests that these clusters are not the byproduct of local gene clustering. We also analyzed the pattern of co-expression among neighboring genes within a single Drosophila species: D. simulans. For the co-expression clusters identified within this species, we find an under-representation of genes displaying a signature of recurrent adaptive amino acid evolution consistent with previous findings. However, clusters displaying co-evolution of expression among species are enriched for adaptively evolving genes. This finding points to a tie between adaptive sequence evolution and evolution of the transcriptome. Conclusion Our results demonstrate that co-evolution of expression in gene clusters is relatively common among species in the D. melanogaster subgroup. We consider the possibility that local regulation of expression in gene clusters may drive the connection between adaptive sequence and coordinated gene expression evolution

Photoionization Of The 6P32,122 Fine-structure Levels In Cesium

The relative photoionization cross sections for cesium atoms selectively excited to the 6P32,122 states have been measured in a triple-crossed-beam experiment. A cesium discharge lamp produced resonant wavelengths of 8521 and 8944 for the excitation process. A Hg-Xe lamp combined with a grating monochromator was used for the actual ionization in the wavelength region from 2500 to 5000. Background counts due to photoionization of ground-state cesium atoms and dimers as well as various surface effects were discriminated against by chopping the excitation light source. The data are compared with results from radiative-recombination measurements in which the fine-structure levels are not resolved and with recent model-potential calculations. The wavelength () dependence of the cross section indicates a 2 dependence at threshold (5000) and a 4 behavior at lower wavelengths. © 1975 The American Physical Society

Next-Generation Mapping of Complex Traits with Phenotype-Based Selection and Introgression

Finding the genes underlying complex traits is difficult. We show that new sequencing technology combined with traditional genetic techniques can efficiently identify genetic regions underlying a complex and quantitative behavioral trait. As a proof of concept we used phenotype-based introgression to backcross loci that control innate food preference in Drosophila simulans into the genomic background of D. sechellia, which expresses the opposite preference. We successfully mapped D. simulans introgression regions in a small mapping population (30 flies) with whole-genome resequencing using light coverage (∼1×). We found six loci contributing to D. simulans food preference, one of which overlaps a previously discovered allele. This approach is applicable to many systems, does not rely on laborious marker development or genotyping, does not require existing high quality reference genomes, and needs only small mapping populations. Because introgression is used, researchers can scale mapping population size, replication, and number of backcross generations to their needs. Finally, in contrast to more widely used mapping techniques like F2 bulk-segregant analysis, our method produces near-isogenic lines that can be kept and reused indefinitely