Temperature-dependent effects of house fly proto-Y chromosomes on gene expression could be responsible for fitness differences that maintain polygenic sex determination

Sex determination, the developmental process by which sexually dimorphic phenotypes are established, evolves fast. Evolutionary turnover in a sex determination pathway may occur via selection on alleles that are genetically linked to a new master sex determining locus on a newly formed proto-sex chromosome. Species with polygenic sex determination, in which master regulatory genes are found on multiple different proto-sex chromosomes, are informative models to study the evolution of sex determination and sex chromosomes. House flies are such a model system, with male determining loci possible on all six chromosomes and a female-determiner on one of the chromosomes as well. The two most common male-determining proto-Y chromosomes form latitudinal clines on multiple continents, suggesting that temperature variation is an important selection pressure responsible for maintaining polygenic sex determination in this species. Temperature-dependent fitness effects could be manifested through temperature-dependent gene expression differences across proto-Y chromosome genotypes. These gene expression differences may be the result of cis regulatory variants that affect the expression of genes on the proto-sex chromosomes, or trans effects of the proto-Y chromosomes on genes elswhere in the genome. We used RNA-seq to identify genes whose expression depends on proto-Y chromosome genotype and temperature in adult male house flies. We found no evidence for ecologically meaningful temperature-dependent expression differences of sex determining genes between male genotypes, but we were probably not sampling an appropriate developmental time-point to identify such effects. In contrast, we identified many other genes whose expression depends on the interaction between proto-Y chromosome genotype and temperature, including genes that encode proteins involved in reproduction, metabolism, lifespan, stress response, and immunity. Notably, genes with genotype-by-temperature interactions on expression were not enriched on the proto-sex chromosomes. Moreover, there was no evidence that temperature-dependent expression is driven by chromosome-wide cis-regulatory divergence between the proto-Y and proto-X alleles. Therefore, if temperature-dependent gene expression is responsible for differences in phenotypes and fitness of proto-Y genotypes across house fly populations, these effects are driven by a small number of temperature-dependent alleles on the proto-Y chromosomes that may have trans effects on the expression of genes on other chromosomes

Water striders adjust leg movement speed to optimize takeoff velocity for their morphology

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.1

New virtual orthodontic treatment system for indirect bonding using the stereolithographic technique

The purpose of this article is to introduce a new virtual orthodontic treatment (VOT) system, which can be used to construct three-dimensional (3D) virtual models, establish a 3D virtual setup, enable the placement of the virtual brackets at the predetermined position, and fabricate the transfer jig with a customized bracket base for indirect bonding (IDB) using the stereolithographic technique. A 26-year-old woman presented with anterior openbite, crowding in the upper and lower arches, and narrow and tapered upper arch, despite having an acceptable profile and balanced facial proportion. The treatment plan was rapid palatal expansion (RPE) without extraction. After 10 days of RPE, sufficient space was obtained for decrowding. After a 10-week retention period, accurate pretreatment plaster models were obtained using silicone rubber impression. IDB was performed according to the protocol of the VOT system. Crowding of the upper and lower arches was effectively resolved, and anterior openbite was corrected to normal overbite. Superimposition of the 3D virtual setup models (3D-VSM) and post-treatment 3D virtual models showed that the latter deviated only slightly from the former. Thus, the use of the VOT system helped obtain an acceptable outcome in this case of mild crowding treated without extraction. More cases should be treated using this system, and the pre- and post-treatment virtual models should be compared to obtain feedback regarding the procedure; this will support doctors and dental laboratory technicians during the learning curve. (Korean J Orthod 2011;41(2):138-146)

Efficient Cultivation Conditions for Human Limbal Epithelial Cells

To compare the stem niche in different culture conditions of limbal epithelial cells, the suspended human limbal epithelial cells (HLECs) were seeded on the 3T3-pretreated plates and the other suspended cells were plated on amniotic membranes (AMs) which were either cryo-preserved or freeze-dried. All were cultured for 10 to 12 days. Reverse transcription-polymerase chain reaction (RT-PCR) for ATP-binding casette, subfamily G, member 2 (ABCG2), p63, cytokeratin 12, and connexin 43 were performed in cultivated HLECs and their expression levels were compared. The mRNA expression of all markers examined showed no statistically significant differences between the cells on cryo-preserved and on freeze-dried AM. The expression of p63 and cytokeratin 12 in cultivated cells on AMs were significantly lower than those in 3T3-cocultured cells on RT-PCR and immunofluorescent staining. Cultivated HLECs on AMs showed reduced proliferation and differentiation while maintaining stem-property regardless of the preservative method of AM

The Evolution of Sex Determination Mechanisms and Sex Chromosomes in House fly, Musca domestica L.

Sex determination (SD) evolves fast, often due to changes in master regulatory SD genes. SD genes are found on sex chromosomes, and evolution of SD can also drive evolutionary turnover of sex chromosomes. As a consequence, young (proto) sex chromosomes are generated, in which the X and Y are minimally diverged from each other. Multiple young sex chromosomes can coexist in species with multiple (polygenic) SD master regulators. Species with polygenic SD are informative of the factors driving the early evolution of sex chromosomes. The house fly, Musca domestica, is a well-suited model to those ends because natural populations have polygenic SD and young sex chromosomes. Natural selection appears to maintain polygenic SD, but the targets of selection are elusive. To address this, I examined the effects of two house fly proto-Y chromosomes (YM and IIIM) on gene expression. I find that the proto-Y chromosomes have minor effects on gene expression, which is paradoxical given that natural selection likely maintains polygenic SD in house fly. I identified evidence for disproportionate effects of the proto-Y chromosomes on sex-biased expression. These few expression differences could be targets upon which natural selection acts to maintain polygenic SD. The frequencies of YM and IIIM vary along latitudinal clines, and I tested whether temperature could explain these clines by examining the expression of SD pathway genes at different developmental temperatures. I did not find differences in expression of the sex-determining genes between YM and IIIM males consistent with the clines. I also found that one house fly proto-Y chromosome is differentiated from its homologous proto-X in the sequences of many genes, but gene expression divergence between the proto-X and proto-Y is limited to a subset of genes. This suggests that subtle gene expression differentiation constitutes the earliest stages of X-Y differentiation. Lastly, I tried constructing a stable line that has females carrying the dominant female-determining Md-traD allele. In this line, all females and males would carry two copies of IIIM. However, I could not create a stable line because males homozygous for IIIM could have low fitness or deleterious effects.Biology and Biochemistry, Department o

Effect of sex, hunger and relative body size on the use of ripple signals in the interactions among water striders Gerris latiabdominis

Water striders use ripple signals in aggressive interactions between individuals for access to food. We asked whether water striders produce ripple signals more frequently when they are hungrier and when the value of food resources is higher. We also asked if and how the use of signals depends on the size difference between interacting individuals. We found that females used ripple signals more often than males did. The experiment suggested that use of aggressive ripple signals is affected by hunger in females – the sex with high demands for food resources. Among females, but not males, we found out that the probability of using signals in response to the approaching intruder depended both on the degree of hunger and on the size of the focal animal relative to the size of the intruder. Before starvation, the probability of a female using a signal in an interaction with an intruder was higher when the individual's size was larger relative to the intruder. After starvation, the focal individuals were more likely to signal when their size was smaller relative to the intruder. The results are consistent with the idea that these signals may reveal information about the signalers weight or hunger level, and specific hypotheses are suggested for the future studies

Pyrosequencing-based Molecular Monitoring of the Intestinal Bacterial Colonization in Preterm Infants

Objectives: The aim of the study was to investigate the previously unexplored diversity of neonatal intestinal microbiota and monitor early intestinal colonization patterns in Korean preterm infants using high-throughput pyrosequencing technology combined with 16S rDNA-based molecular methods. Subjects and Methods: A total of 46,369 partial 16S rDNA sequences obtained from 30 fecal samples serially taken from 10 very-low-birth weight preterm infants were analyzed. Results: A significant proportion of the molecular species (21.9%) was found to be unclassified. The pathogenic or potentially pathogenic molecular species belonging to the classes Gammaproteobacteria and Bacilli were predominant during the entire observation period. Anaerobic or nonpathogenic molecular species belonging to the class Clostridia (except Clostridium difficile) and phyla Bacteroidetes were ubiquitous even within 72 hours after birth. The proportion of these species increased significantly at 1 month of age. The most ubiquitous and abundant major molecular genera common to all of the postnatal ages were Escherichia, Enterobacter, Enterococcus, Veillonella, Serratia, Staphylococcus, Roseburia, Acinetobacter, Citrobacter, Bacteroides, Faecalibacterium, Blautia, and Streptococcus. Conclusions: The diversity and dynamic nature of intestinal bacterial colonization in very-low-birth weight preterm infants were revealed using pyrosequencing technology. The results of the present pilot study may provide a basis to consider when investigating or interpreting the role of intestinal microbiota in certain preterm infant diseases such as necrotizing enterocolitis or systemic infection.