Mandibular Fracture Patterns at a Medical Center in Central Taiwan: A 3-Year Epidemiological Review

Mandibular fractures constitute a major portion of maxillofacial trauma and may lead to considerable functional and aesthetic sequelae if treatment is inadequate or delayed. An epidemiology study on mandibular fractures may guide the preventive efforts of the Taiwan public health care system. Therefore, a retrospective review was conducted at a medical center in central Taiwan to evaluate the current mandibular fracture epidemiology.The medical records and digitized radiographs of 198 patients who received treatment for mandibular fractures during a 3-year period (from October 2010 to September 2013) at a medical center in central Taiwan were reviewed to obtain demographic and injury data.The average age was 29.4 years (3-82 years). Patients aged 21 to 30 years sustained the most mandibular fractures (62 patients, 31.3%). The overall sex distribution (male to female) ratio was 1.8. Motor-vehicle accidents (MVAs) were the most common mechanism of injury (162 patients, 82%), and scooter and motorcycle riders wearing partial-coverage helmets constituted the majority of patients. A chart review identified 198 patients with 335 mandibular fractures; 113 patients (57.1%) had multiple mandibular fractures. The most common fracture sites were the symphysis and parasymphysis regions (38.9%), followed by the condyle (26.0%), angle (14.3%), body (14.3%), and ramus (6.6%).MVAs are the major cause of mandibular fractures in central Taiwan, and patients aged <30 years sustained the most mandibular fractures. Compared with previous studies, the present study has a higher percentage of women with mandibular fractures. In addition, inadequate mandibular protection by partial-coverage helmets may be a major reason for mandibular fractures most commonly localized in the symphysis and parasymphysis regions. The incidence and causes of mandibular fractures may reflect the trauma patterns within the community, thus facilitating the development of a preventive strategy for the socioeconomic and environmental background of central Taiwan.

Coincidence or complication? A systematic review of trigger digit after carpal tunnel release

BACKGROUND

Carpal tunnel syndrome (CTS) and trigger digits are among the most common nontraumatic hand disorders treated by plastic surgeons. The onset of trigger digits after carpal tunnel release (CTR) has been inconsistently reported. This systematic review assessed the prevalence of trigger digits development in patients after CTR surgery.

METHODS

We searched the MEDLINE, EMBASE and SCOPUS databases for papers published between January 1966 and August 2016. Eligible studies contained quantitative data on the incidence of trigger digits after CTR. The primary outcome measure was the onset of trigger digits after CTR. The secondary outcome measure was the prevalence of digital involvement in patients who developed trigger digits after CTR.

RESULTS

A total of 5654 CTR surgeries were performed in the included nine studies, and 483 patients (8.5%) developed trigger digits after CTR. The reported incidence of trigger digits after CTR ranged from 5.2% to 31.7%. The time to development of trigger digits was approximately 6 months postoperatively. In the eight observational studies and in the randomized controlled trial, the thumb and ring finger were reported as the most commonly involved trigger digits, respectively.

CONCLUSIONS

The incidence of trigger digits after CTR surgery is not negligible. Thumbs and ring fingers are the most commonly involved digits. This topic should therefore be suitably addressed during preoperative consultations.

Efficacy and safety of negative pressure wound therapy for Szilagyi grade III peripheral vascular graft infection

A best evidence topic in vascular surgery was written according to a structured protocol. The question addressed was whether it is safe and effective to use negative pressure wound therapy (NPWT) for Szilagyi grade III (i.e. the arterial implant proper involved in the infection) peripheral vascular graft infection. Altogether, 69 papers were found using the reported search. From the search results, reference lists of potentially eligible studies and related citations in PubMed, seven papers represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. In the only randomized, controlled trial that compared NPWT (n = 10) and alginate dressing change (n = 10), the NPWT group demonstrated shorter time to full skin epithelialization (median 57 vs 104 days; P = 0.026). In the other six case series, the recruited case number ranged from 12 to 72. The mode of NPWT varied among the included studies, with the majority using a continuous negative pressure of 125 mmHg. One study combined NPWT and sartorius myoplasty, another used sartorius myoplasty in selected cases and others did not. The mean duration of using NPWT ranged from 14.2 to 43 days. The mean duration to achieve complete wound healing ranged from 24 (the study with sartorius myoplasty) to 51 days. The NPWT treatment failure rate ranged from 0 (the study with sartorius myoplasty) to 25%. The major complication of NPWT was bleeding and the incidence rate was reported to be <10%. We conclude that the amount of evidence for recommending NPWT alone as the first-line treatment for Szilagyi grade III peripheral vascular graft infection is small with only one small-sized randomized controlled trial demonstrating that NPWT alone is superior to alginate dressing change in shortening the time to complete wound healing by 2 months. Limited evidence (case series with >1 year of follow-up) showed that NPWT with a continuous negative pressure of 125 mmHg, or combined NPWT and sartorius myoplasty, may shorten the time to complete wound healing by 2 months, have a >70% success rate, and have a <10% NPWT-related complication rate.

Selfish genetic elements

Complex genetic systems appear to be inherently vulnerable to subversion by 'selfish' genetic elements, which gain a transmission advantage relative to the rest of the genome and are often detrimental to the organism. Such elements appear to have evolved many times, and show diverse origins and mechanisms for gaining a transmission advantage. The purpose of this report is to indicate how widespread such selfish genetic elements are, and to review the main evolutionary and population genetic questions relating to them.

Association of DNA double-strand break gene XRCC6 genotypes and lung cancer in Taiwan

AIM

The DNA repair gene X-ray repair complementing defective repair in Chinese hamster cells 6 (XRCC6) is thought to play an important role in the repair of DNA double-strand breaks. It is known that defects in double-strand break repair capacity can lead to irreversible genomic instability. However, the association of polymorphic variants of XRCC6 with lung cancer susceptibility has never been reported. In this hospital-based case-control study, the association of XRCC6 promoter T-991C (rs5751129), promoter G-57C (rs2267437), promoter G-31A (rs132770), and intron 3 (rs132774) polymorphisms with lung cancer risk in a Taiwanese population, was studied.

MATERIALS AND METHODS

In total, 358 patients with lung cancer and 716 healthy controls recruited from the China Medical Hospital in Taiwan were genotyped.

RESULTS

The results showed that there were significant differences between lung cancer and control groups in the distribution of their genotypic (p=3.7×10(-4)) and allelic frequency (p=2.7×10(-5)) in the XRCC6 promoter T-991C polymorphism. Individuals who carried at least one C allele (TC or CC) had a 2.03-fold increased odds ratio of developing lung cancer compared to those who carried the wild-type TT genotype (95% conference internal=1.42-2.91, p=0.0001). For the other three polymorphisms, there was no difference between the case and control groups in the distribution of either genotypic or allelic frequency.

CONCLUSION

In conclusion, the XRCC6 promoter T-991C, but not the promoter C-57G, promoter G-31A or intron 3, is associated with lung cancer susceptibility.

Significant association of caveolin-1 (CAV1) genotypes with breast cancer in Taiwan

AIM

Japanese and American groups reported that single nucleotide variation of caveolin-1 gene (CAV1) plays an important role in breast cancer risk. The aim of this study was to evaluate the association of six polymorphic genotypes of CAV1, which is reported to be overexpressed in tumors, with breast cancer within a Taiwanese population.

PATIENTS AND METHODS

A total of 1232 patients with breast cancer and equal number of healthy controls in central Taiwan were genotyped via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) and six polymorphic variants of CAV1 were analyzed for their association with breast cancer susceptibility.

RESULTS

The distribution of genotypes of CAV1 G14713A and T29107A were significantly different between breast cancer and control groups (p=5.6×10(-5) and 1.9×10(-4), respectively), while those for CAV1 C239A, G21985A, T28608A and G32124A were not significant (p>0.05). The percentages of AG genotype of G14713A and TT genotype of T29107A are higher in the cancer group than in the control group. The two single nucleotide polymorphisms were chosen for haplotype analysis and the data showed that compared with GG/TT haplotype of CAV1 G14713A/T29107A, the GG/AT and GG/AA groups have a lower risk of breast cancer (odds ratio, OR=0.69, 95% confidence interval, CI=0.57-0.92). On the contrary, the AG/TT haplotype confers a higher risk of breast cancer (OR=1.50, 95% CI=1.14-2.12).

CONCLUSION

Our results provide evidence for CAV1 genotypes being involved in predisposition to breast cancer. The association of the potential risk haplotype agrees well with a role of CAV1 genotype in breast cancer risk and the association with tumor progression needs further investigation.

Association of Alpha B-Crystallin (CRYAB) genotypes with breast cancer susceptibility in Taiwan

AIM

Alpha B-Crystallin (CRYAB) is purported to be a metastasis suppressor protein, and lack or lower CRYAB expression is a prognostic biomarker for several types of cancer, such as that of the prostate and head and neck. However, the association of genomic variation of CRYAB and breast cancer is not well studied. The aim of this study was to evaluate the association of polymorphic genotypes of CRYAB with breast cancer within a Taiwanese population.

PATIENTS AND METHODS

In this hospital-based study, 1232 patients with breast cancer and an equal number of healthy controls in central Taiwan were genotyped via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) and the association of CRYAB A-1215G (rs2228387), C-802G (rs14133) and intron 2 (rs2070894) polymorphisms with breast cancer risk in a central Taiwanese population was investigated.

RESULTS

Those individuals with CRYAB C-802G CG and GG genotypes had 1.50- and 2.22-fold risk for breast cancer than those with the CC genotype. As for the A-1215G and intron 2 polymorphisms, there was no significant association of the genotype with breast cancer risk. In allelic frequency analysis, the G allele CRYAB C-802G conferred a significantly (p=5.63×10(-10)) increased risk of breast cancer. Our results provide evidence that the G allele of CRYAB C-802G is correlated with breast cancer risk and this polymorphism may be a useful marker for early detection of breast cancer in clinical practice.

Virility Deficiency and the Sex-Ratio Trait in DROSOPHILA PSEUDOOBSCURA. I. Sperm Displacement and Sexual Selection

The Sex-Ratio (SR) phenomenon is associated with the X chromosome of many species of Drosophila. Males carrying SR transmit predominantly sperm bearing the X chromosome. SR, therefore, has a very significant advantage in segregation. This paper provides an experimental analysis of the role of virility selection in preventing the fixation of SR. SR males are found to suffer substantial virility reduction when mated with nonvirgin females but not with virgin females. The reduced virility arises because they are weaker in sperm displacement and are discriminated against by nonvirgin females. The virility deficiency of SR males is even more severe at low temperatures.

Virility Deficiency and the Sex-Ratio Trait in DROSOPHILA PSEUDOOBSCURA. II. Multiple Mating and Overall Virility Selection

Previous studies on fitness components of Drosophila have shown the over-whelming importance of virility selection. In this study, virility selection is further partitioned into two components-one with respect to virgin females and the other with respect to nonvirgin females. The relative importance of the two components to the overall virility selection depends on the remating tendency of females which is investigated here. A theoretical model is then proposed to estimate virility selection under the condition of frequent female remating. The model is tested experimentally. When this model is applied to the Sex-Ratio system of D. pseudoobscura, Sex-Ratio males are found to suffer substantial virility reduction. The significance of this finding to the Sex-Ratio problem is discussed.

Tension pneumocephalus: a rare complication after hyperbaric oxygen therapy

The study aimed to describe a patient with multiple skull bone fractures and a cerebrospinal fluid (CSF) leak who received hyperbaric oxygen therapy (HBOT). A 40-year-old man presented with subdural hemorrhage, skull bone fractures, facial bone fractures, sinus fractures, and CSF leakage after a one-story fall. He received HBOT as an adjunctive treatment to reduce brain edema and increase oxygen availability in brain tissue. Tension pneumocephalus developed after HBOT. Bur hole drainage was performed emergently to relieve the tension pneumocephalus. Cranioplasty and repair of skull base fracture were subsequently performed. The patient was discharged in a vegetative state. We proposed a possible mechanism by which tension pneumocephalus developed after HBOT sessions in this patient. Pneumocephalus, untreated skull base fracture, and CSF leakage should be considered contraindications to HBOT.

E-cadherin gene 3'-UTR C/T polymorphism is associated with prostate cancer

INTRODUCTION

E-cadherin (CDH-1) is a cell-cell adhesive molecule which maintains cell integrity and communication between the intracellular and extracellular world. CDH-1 may therefore be related to carcinogenesis. A polymorphism located at the 3'-UTR of the CDH-1 gene is associated with stone disease; however, its relationship to prostate cancer has not been reported. We aimed to study whether there is an association between the 3'-UTR polymorphism and prostate cancer.

MATERIALS AND METHODS

We collected 96 patients with prostate cancer and 114 normal controls for this study. The polymorphism of the CDH-1 gene was studied by polymerase chain reaction-based restriction analysis.

RESULTS

There was a significant difference in genotype distribution of the CDH-1 gene polymorphism between cancer patients and normal controls (p < 0.001). The distribution of the CDH-1 gene CC genotype in prostate cancer patients (51.0%) was higher than in the controls (10.5%). The odds ratio for the CDH-1 'C' allele was 2.896 (95% CI = 1.908-4.396). There was no significant difference according to age, pathological grading, clinical staging, and responsiveness to hormonal therapy among patients. Only 3 patients (3.1%) had a history of urolithiasis.

CONCLUSIONS

The CDH-1 gene 3'-UTR C/T polymorphism is associated with prostate cancer. The 'CC' homozygote indicates a relatively higher risk for developing prostate cancer than other genotypes.

Usefulness of 99mTc ethyl cysteinate dimer brain SPECT to detect abnormal regional cerebral blood flow in patients with acute carbon monoxide poisoning

99mTc ethyl cysteinate dimer (99mTc-ECD) brain single photon emission computed tomography (SPECT) was used to detect abnormal regional cerebral blood flow (rCBF) in patients with acute carbon monoxide (CO) poisoning. Ten patients with acute CO poisoning and no past histories of psychoneurological disorders were enrolled in this study. After oxygen treatment, all of the 10 patients were investigated using 99mTc-ECD brain SPECT and brain computed tomography (CT) scan. Brain CT scan findings were normal in all of the 10 patients. 99mTc-ECD brain SPECT showed the hypoperfusion lesions of the basal ganglia and brain cortex in five and seven patients, respectively. Only three of the 10 patients had normal 99mTc-ECD brain SPECT findings. This study suggests that, in comparison with brain CT scan, 99mTc-ECD brain SPECT is a better tool for the early detection of hypoperfusion brain lesions in acute CO poisoning in patients with normal brain CT findings.

The neutral theory in the genomic era

A number of tests have been developed to detect positive selection at the molecular level. These tests are based on DNA polymorphism within and divergence between species. Applications of these tests have revealed a large collection of genes that have evolved under positive selection and some general insights into adaptive evolution. Recently, these tests have been applied on a genomic scale and have provided estimates of the frequency of adaptive substitutions and a critical test of the neutral theory.

Modeling linkage disequilibrium between a polymorphic marker locus and a locus affecting complex dichotomous traits in natural populations

Linkage disequilibrium is an important topic in evolutionary and population genetics. An issue yet to be settled is the theory required to extend the linkage disequilibrium analysis to complex traits. In this study, we present theoretical analysis and methods for detecting or estimating linkage disequilibrium (LD) between a polymorphic marker locus and any one of the loci affecting a complex dichotomous trait on the basis of samples randomly or selectively collected from natural populations. Statistical properties of these methods were investigated and their powers were compared analytically or by use of Monte Carlo simulations. The results show that the disequilibrium may be detected with a power of 80% by using phenotypic records and marker genotype when both the trait and marker variants are common (30%) and the LD is relatively high (40-100% of the theoretical maximum). The maximum-likelihood approach provides accurate estimates of the model parameters as well as detection of linkage disequilibrium. The likelihood method is preferred for its higher power and reliability in parameter estimation. The approaches developed in this article are also compared to those for analyzing a continuously distributed quantitative trait. It is shown that a larger sample size is required for the dichotomous trait model to obtain the same level of power in detecting linkage disequilibrium as the continuous trait analysis. Potential use of these estimates in mapping the trait locus is also discussed.

Positive and negative selection on the human genome

The distinction between deleterious, neutral, and adaptive mutations is a fundamental problem in the study of molecular evolution. Two significant quantities are the fraction of DNA variation in natural populations that is deleterious and destined to be eliminated and the fraction of fixed differences between species driven by positive Darwinian selection. We estimate these quantities using the large number of human genes for which there are polymorphism and divergence data. The fraction of amino acid mutations that is neutral is estimated to be 0.20 from the ratio of common amino acid (A) to synonymous (S) single nucleotide polymorphisms (SNPs) at frequencies of > or =15%. Among the 80% of amino acid mutations that are deleterious at least 20% of them are only slightly deleterious and often attain frequencies of 1-10%. We estimate that these slightly deleterious mutations comprise at least 3% of amino acid SNPs in the average individual or at least 300 per diploid genome. This estimate is not sensitive to human population history. The A/S ratio of fixed differences is greater than that of common SNPs and suggests that a large fraction of protein divergence is adaptive and driven by positive Darwinian selection.

Incipient speciation by sexual isolation in Drosophila: concurrent evolution at multiple loci

Drosophila melanogaster from Zimbabwe and nearby regions shows strong but asymmetric sexual isolation from its cosmopolitan counterparts. By creating stable chromosome-substitution lines, earlier studies were able to show that the two major autosomes have very large effects on both male mating success and female mating preference. In this study, we genetically dissect this sexual isolation by recombination analysis between a whole-chromosome substitution line (which carries a Zimbabwe-derived third chromosome) and a strain with seven visible markers on that chromosome. Four loci are responsible for male mating success and three others are found to control female mating preference. Because male and female traits are not closely linked, their strong association among isofemale lines is most likely a reflection of sexual selection in nature. The results suggest that a large number of behavioral loci may evolve concurrently in the incipient stage of speciation before other aspects of reproductive isolation (such as hybrid sterility) have become evident. The results shed light on the population genetic processes underlying the formation of nascent species, as well as modes of speciation.

Gametic incompatibilities between races of Drosophila melanogaster

Reproductive-isolating mechanisms between nascent species may involve sperm-egg recognition and have been best described in externally fertilizing organisms where such recognition is essential in preventing undesirable fertilizations. However, reproductive barriers in internally fertilizing species differ in significant ways, and a direct role for sperm-egg interactions has yet to be demonstrated. Females of many strains of Drosophila melanogaster from Zimbabwe, Africa, do not mate readily with cosmopolitan males. This polymorphism in mate choice is postulated to represent incipient speciation. We now report that, in one direction, crosses between the above populations produce far fewer offspring than reciprocal crosses due to a lower rate of egg hatch. We established that egg inviability in these crosses was due to defects in fertilization. Thus, even in taxa with internal fertilization, gametic incompatibility may be a mechanism relevant to reproductive isolation during incipient speciation.

The nucleotide changes governing cuticular hydrocarbon variation and their evolution in Drosophila melanogaster

The cuticular hydrocarbon (CH) pheromones in Drosophila melanogaster exhibit strong geographic variation. African and Caribbean populations have a high ratio of 5,9 heptacosadiene/7,11 heptacosadiene (the "High" CH type), whereas populations from all other areas have a low ratio ("Low" CH type). Based on previous genetic mapping, DNA markers were developed that localized the genetic basis of this CH polymorphism to within a 13-kb region. We then carried out a hierarchical search for diagnostic nucleotide sites starting with four lines, and increasing to 24 and 43 lines from a worldwide collection. Within the 13-kb region, only one variable site shows a complete concordance with the CH phenotype. This is a 16-bp deletion in the 5' region of a desaturase gene (desat2) that was recently suggested to be responsible for the CH polymorphism on the basis of its expression [Dallerac, R., Labeur, C., Jallon, J.-M., Knipple, D. C., Roelofs, W. L. & Wicker-Thomas, C. (2000) Proc. Natl. Acad. Sci. 97, 9449--9454]. The cosmopolitan Low type is derived from the ancestral High type, and DNA sequence variations suggest that the former spread worldwide with the aid of positive selection. Whether this CH variation could be a component of the sexual isolation between Zimbabwe and other cosmopolitan populations remains an interesting and unresolved question.

Sex in Drosophila mauritiana: a very high level of amino acid polymorphism in a male reproductive protein gene, Acp26Aa

Many genes pertaining to male reproductive functions have been shown to evolve rapidly between species, and evidence increasingly suggest the influence of positive Darwinian selection. The accessory gland protein gene (Acp26Aa) of Drosophila is one such example. In order to understand the mechanism of selection, it is often helpful to examine the pattern of polymorphism. We report here that the level of amino acid polymorphism in the N-terminal quarter of Acp26Aa is high in Drosophila melanogaster and is unprecedented in its sibling species Drosophila mauritiana. We postulate that (1) this N-terminal segment may play a role in sperm competition, and (2) D. mauritiana may have been under much more intense sexual selection than other species. Both postulates have important ramifications and deserve to be tested rigorously.

Hitchhiking under positive Darwinian selection

Positive selection can be inferred from its effect on linked neutral variation. In the restrictive case when there is no recombination, all linked variation is removed. If recombination is present but rare, both deterministic and stochastic models of positive selection show that linked variation hitchhikes to either low or high frequencies. While the frequency distribution of variation can be influenced by a number of evolutionary processes, an excess of derived variants at high frequency is a unique pattern produced by hitchhiking (derived refers to the nonancestral state as determined from an outgroup). We adopt a statistic, H, to measure an excess of high compared to intermediate frequency variants. Only a few high-frequency variants are needed to detect hitchhiking since not many are expected under neutrality. This is of particular utility in regions of low recombination where there is not much variation and in regions of normal or high recombination, where the hitchhiking effect can be limited to a small (<1 kb) region. Application of the H test to published surveys of Drosophila variation reveals an excess of high frequency variants that are likely to have been influenced by positive selection.

The phylogeny of closely related species as revealed by the genealogy of a speciation gene, Odysseus

Molecular differentiation between races or closely related species is often incongruent with the reproductive divergence of the taxa of interest. Shared ancient polymorphism and/or introgression during secondary contact may be responsible for the incongruence. At loci contributing to speciation, these two complications should be minimized (1, 2); hence, their variation may more faithfully reflect the history of the species' reproductive differentiation. In this study, we analyzed DNA polymorphism at the Odysseus (OdsH) locus of hybrid sterility between Drosophila mauritiana and Drosophila simulans and were able to verify such a prediction. Interestingly, DNA variation only a short distance away (1.8 kb) appears not to be influenced by the forces that shape the recent evolution of the OdsH coding region. This locus thus may represent a test case of inferring phylogeny of very closely related species.

Genetic analysis of speciation by means of introgression into Drosophila melanogaster

In the last decade, the genetic basis of reproductive isolation has been shown to be surprisingly polygenic, and yet even the most efficient system currently in use could lend itself to molecular analysis only in highly selected cases. By extending the recent discovery of fertility rescue between Drosophila melanogaster and Drosophila simulans, we show that this hybridization can permit systematic and precise delineation of the genetic and molecular basis of speciation. In a region of 5% of the D. simulans genome introgressed into D. melanogaster, we discover at least six genes of hybrid male sterility and none for female sterility by deficiency mapping. A single case of hybrid inviability has been tracked down to a 3-Kb element that was inserted into the Cyclin E locus during species hybridization. The extent of interspecific genetic divergence underlying hybrid male sterility, especially in contrast with the low degree of inviability and female sterility, is far greater than expected from previous studies.

Rapid evolution of male reproductive genes in the descent of man

A diverse body of morphological and genetic evidence has suggested that traits pertaining to male reproduction may have evolved much more rapidly than other types of character. Recently, DNA sequence comparisons have also shown a very high level of divergence in male reproductive proteins between closely related Drosophila species, among marine invertebrates and between mouse and rat. Here we show that rapid evolution of male reproductive genes is observable in primates and is quite notable in the lineages to human and chimpanzee. Nevertheless, rapid evolution by itself is not necessarily an indication of positive darwinian selection; relaxation of negative selection is often equally compatible with the DNA sequence data. By taking three statistical approaches, we show that positive darwinian selection is often the driving force behind this rapid evolution. These results open up opportunities to test the hypothesis that sexual selection plays some role in the molecular evolution of higher primates.

PE-PEG/LEH can reduce its interactions with plasma expanders indexed through viscosity measurements

To investigate whether PE-PEG coated LEH (PE-PEG/LEH) can reduce its interaction with different plasma expanders and possibly suspended in those expanders, we measured the viscosity of PE-PEG/LEH suspended in different plasma expanders as an index for the interactions. The results showed that lower viscosity values for PE-PEG/LEH were observed compared with LEH especially in low shear rate regions (e.g., 7.72 +/- 1.46 cp vs. 14.91 +/- 1.03 cp for gamma = 2.25 sec-1, respectively). Moreover, the viscosity values for PE-PEG/LEH suspended in fibrinogen suspensions were much less than those of LEH in the same media at low shear rate regions (e.g., 7.72 +/- 1.59 cp vs. 25.78 +/- 1.59 cp, gamma = 2.25 sec-1, respectively). Similar results were observed for PE-PEG/LEH suspended in 1.83% of oxypolygelatin (Gel) suspensions and 1.5% hydrooxyethyl starch (HES) compared to LEH in the same suspension media. On contrast, PE-PEG/LEH suspended in dextran (Dex) showed that dramatically increasing the viscosity values in low shear rates compared with LEH suspended in the same media (e.g., 78.87 +/- 0.56 cp vs. 51.08 +/- 3.52 cp, gamma = 2.25 sec-1, respectively) were observed. Since only minor interactions with Gel, HES or fibrinogen suspensions were observed, we suggest that PE-PEG/LEH suspended in those media but not in Dex can possibly serve for resuscitation oxygen-carrying fluids.

A rapidly evolving homeobox at the site of a hybrid sterility gene

The homeodomain is a DNA binding motif that is usually conserved among diverse taxa. Rapidly evolving homeodomains are thus of interest because their divergence may be associated with speciation. The exact site of the Odysseus (Ods) locus of hybrid male sterility in Drosophila contains such a homeobox gene. In the past half million years, this homeodomain has experienced more amino acid substitutions than it did in the preceding 700 million years; during this period, it has also evolved faster than other parts of the protein or even the introns. Such rapid sequence divergence is driven by positive selection and may contribute to reproductive isolation.

Positive selection driving the evolution of a gene of male reproduction, Acp26Aa, of Drosophila: II. Divergence versus polymorphism

The evolution of the gene for a male ejaculatory protein, Acp26Aa, has been shown to be driven by positive selection when nonsibling species in the Drosophila melanogaster subgroup are compared. To know if selection has been operating in the recent past and to understand the details of its dynamics, we obtained DNA sequences of Acp26Aa and the nearby Acp26Ab gene from 39 D. melanogaster chromosomes. Together with the 10 published sequences, we analyzed 49 sequences from five populations in four continents. The southern African population is somewhat differentiated from all other populations, but its nucleotide diversity is lower at these two loci. We find the following results for Acp26Aa: (1) The R: S (replacement : silent changes) ratio is significantly higher in the between-species comparisons than in the within-species data by the McDonald and Kreitman test. Positive selection is probably responsible for the excess of amino acid replacements between species. (2) However, within-species nucleotide diversity is high. Neither the Tajima test nor the Fu and Li test indicates a reduction in nucleotide diversity due to positive selection in the recent past. (3) The newly derived nucleotides in D. melanogaster are at high frequency significantly more often than predicted by the neutral equilibrium. Since the nearby Acp26Ab gene does not show these patterns, these observations cannot be attributed to the characteristics of this chromosomal region. We suggest that positive selection is active, but may be weak, for each amino acid change in the Acp26Aa gene.

Incipient speciation by sexual isolation in Drosophila melanogaster: extensive genetic divergence without reinforcement

The collection of Drosophila melanogaster from Zimbabwe and nearby regions (the Z-type) yield females who would not mate with the cosmopolitan D. melanogaster males (the M-type). To dissect the genetic basis of this sexual isolation, we constructed 16 whole-chromosome substitution lines between two standard Z- and M-lines. The results were as follows: (1) All substitution lines appear normal in viability and fertility in both sexes, indicating no strong postmating isolation. (2) The genes for the behaviors are mapped to all three major chromosomes with the same ranking and comparable magnitude of effects for both sexes: III > II >> X > or = 0 (III, II and X designate the effects of the three chromosomes). The results suggest less evolution on the X than on autosomes at loci of sexual behavior. (3) The genes for "Z-maleness" are many and somewhat redundant. Whole-chromosome effects for Z-maleness appear nearly additive and show little dominance. (4) In contrast, "Z-femaleness" has less redundancy as partial genotypes never exhibit full phenotypic effects. Epistatic interactions and incomplete dominance can sometimes be detected. (5) The extensive genetic divergence underlying sexual isolation has evolved in the absence of detectable reduction in hybrid fitnesses. Sexual selection has apparently been a driving force of multiple facets of speciation at the nascent stage without reinforcement.

Positive selection and the molecular evolution of a gene of male reproduction, Acp26Aa of Drosophila

The gene for a male ejaculatory protein, Acp26Aa, in four sibling species of the Drosophila melanogaster subgroup has previously been shown to have a nonsynonymous rate (Ka) of nucleotide substitution that is indistinguishable from the synonymous rate (Ks). By examining this gene in two other species of this subgroup, we found that Ka is generally large and can sometimes be more than twice as large as Ks. This suggests that positive selection may be operating at this locus of male reproduction.

Discord between the phylogenies inferred from molecular versus functional data: uneven rates of functional evolution or low levels of gene flow?

According to measures of molecular divergence, the three species of the Drosophila simulans clade are closely related to and essentially equidistant from each other. We introgressed 10% of the D. sechellia X chromosome into a pure D. simulans genetic background and found that males carrying this introgressed region were consistently fertile; in contrast, males carrying the same segment from D. mauritiana are sterile and suffer from incompatibilities at a minimum of four loci. Together with other recent results, these data suggest that D. simulans and D. sechellia are much more closely related to each other than either is to D. mauritiana. How can we reconcile the phylogeny inferred from the density of hybrid sterility genes with that inferred from molecular divergence? If the molecular phylogeny is correct, the discrepancy might be explained by uneven rates of functional evolution, resulting in the uneven accumulation of substitutions with corresponding negative effects in hybrids. If the functional phylogeny is correct, then low levels of gene flow across nascent species boundaries, particularly for loci not tightly linked to a hybrid sterility gene, may have erased the original pattern of lineage splitting. We propose tests that will allow us to discriminate between these hypotheses.

Rapid evolution of a coadapted gene complex: evidence from the Segregation Distorter (SD) system of meiotic drive in Drosophila melanogaster

Segregation Distorter (SD) is a system of meiotic drive found in natural populations of Drosophila melanogaster. Males heterozygous for an SD second chromosome and a normal homologue (SD+) produce predominantly SD-bearing sperm. The coadapted gene complex responsible for this transmission advantage spans the second chromosome centromere, consisting of three major and several minor interacting loci. To investigate the evolutionary history of this system, we surveyed levels of polymorphism and divergence at six genes that together encompass this pericentromeric region and span seven map units. Interestingly, there was no discernible divergence between SD and SD+ chromosomes for any of these molecular markers. Furthermore, SD chromosomes harbored much less polymorphism than did SD+ chromosomes. The results suggest that the SD-system evolved recently, swept to appreciable frequencies worldwide, and carried with it the entire second chromosome centromeric region (roughly 10% of the genome). Despite its well-documented genetic complexity, this coadapted system appears to have evolved on a time scale that is much shorter than can be gauged using nucleotide substitution data. Finally, the large genomic region hitchhiking with SD indicates that a multilocus, epistatically selected system could affect the levels of DNA polymorphism observed in regions of reduced recombination.

The broom of the sorcerer's apprentice: the fine structure of a chromosomal region causing reproductive isolation between two sibling species of Drosophila

How many genes contribute to reproductive isolation between closely related species? We determined the number of genes located in the 9D-12B region of the Drosophila mauritiana X chromosome that cause hybrid male sterility in a D. simulans background. Previous low resolution studies suggested that a single hybrid sterility factor was associated with this region. In this study, by taking advantage of a cluster of visible and DNA markers, we identified three D. mauritiana factors in this region and then subjected one of them to detailed analysis. This factor again turned out to be comprised of three factors; one of which, mapped to within 200 kb, may in fact be two factors. The title refers to this exercise of splitting sterile introgressions into ever smaller ones, each of which retains partial or full sterility effects. In a region representing a mere 3% of the Drosophila genome, no fewer than six loci of hybrid sterility were identified between two sibling species that have not shown clear divergence at the molecular level. These results suggest that levels of genetic divergence between closely related species may be quite high for functionally important traits even when the opposite is true for randomly chosen loci.

The genetics of reproductive isolation in the Drosophila simulans clade: X vs. autosomal effects and male vs. female effects

A strong effect of homozygous autosomal regions on reproductive isolation was found for crosses between the species in the Drosophila simulans clade. Second chromosome regions were introgressed from D. mauritiana and D. sechellia into D. simulans and tested for their homozygous effects on hybrid male and hybrid female sterility and inviability. Most introgressions are fertile as heterozygotes, yet produce sterile male offspring when made homozygous. The density of homozygous autosomal factors contributing to hybrid male sterility is comparable to the density of X chromosome factors for this level of resolution. Female sterility was also revealed, yet the disparity between male and female levels of sterility was great, with male sterility being up to 23 times greater than female sterility. Complete hybrid inviability was also associated with some regions of the second chromosome, yet there were no strong sex differences. In conclusion, we find no evidence to support a strong X chromosome bias in the evolution of hybrid sterility or inviability but do find a very strong sex bias in the evolution of hybrid sterility. In light of these findings, we reevaluate the current models proposed to explain the genetic pattern of reproductive isolation.

Further characterization of the Odysseus locus of hybrid sterility in Drosophila: one gene is not enough

Previously we mapped by genetical and molecular means a gene that contributes to hybrid-male sterility between Drosophila mauritiana and D. simulans to the cytological interval of 16D. In this report, we refine the mapping of this gene, Odysseus (Ods) and show that it can be delineated to a region the size of an average gene. We further demonstrate that, while Ods appears to be a discrete element, it requires other nearby gene(s) to be cointrogressed to confer full hybrid sterility effect. This observation is in agreement with the view that reproductive isolation between closely related species of Drosophila is usually caused by several genes of weak effect from the same species that interact strongly among themselves as well as with the foreign genetic background.

Sexual isolation in Drosophila melanogaster: a possible case of incipient speciation

It is generally believed that Drosophila melanogaster has no closely related species with which it can produce the viable and fertile hybrids that are essential for the genetic analysis of speciation. Following the recent report of molecular differentiation between a Zimbabwe, Africa, population and two United States populations, we provide evidence that strong sexual isolation exists between the D. melanogaster population in Zimbabwe and populations of other continents. In the presence of males of their own kind, females from most isofemale lines of Zimbabwe would not mate with males from elsewhere; the reciprocal mating is also significantly reduced, but to a lesser degree. The genes for sexual behaviors are apparently polymorphic in Zimbabwe and postmating reproductive isolation between this and other populations has not yet evolved. Whole chromosome substitutions indicate significant genetic contributions to male mating success by both major autosomes, whereas the X chromosome effect is too weak to measure. In addition, the relative mating success between hybrid and pure line males supports the interpretation of strong female choice. These observations suggest that we are seeing the early stages of speciation in this group and that it is driven by sexual selection. The genetic and molecular tractability of D. melanogaster offers great promise for the detailed analysis of this apparent case of incipient speciation.

Genetics of hybrid male sterility between drosophila sibling species: a complex web of epistasis is revealed in interspecific studies

To study the genetic differences responsible for the sterility of their male hybrids, we introgressed small segments of an X chromosome from Drosophila simulans into a pure Drosophila mauritiana genetic background, then assessed the fertility of males carrying heterospecific introgressions of varying size. Although this analysis examined less than 20% of the X chromosome (roughly 5% of the euchromatic portion of the D. simulans genome), and the segments were introgressed in only one direction, a minimum of four factors that contribute to hybrid male sterility were revealed. At least two of the factors exhibited strong epistasis: males carrying either factor alone were consistently fertile, whereas males carrying both factors together were always sterile. Distinct spermatogenic phenotypes were observed for sterile introgressions of different lengths, and it appeared that an interaction between introgressed segments also influenced the stage of spermatogenic defect. Males with one category of introgression often produced large quantities of motile sperm and were observed copulating, but never inseminated females. Evidently these two species have diverged at a large number of loci which have varied effects on hybrid male fertility. By extrapolation, we estimate that there are at least 40 such loci on the X chromosome alone. Because these species exhibit little DNA-sequence divergence at arbitrarily chosen loci, it seems unlikely that the extensive functional divergence observed could be due mainly to random genetic drift. Significant epistasis between conspecific genes appears to be a common component of hybrid sterility between recently diverged species of Drosophila. The linkage relationships of interacting factors could shed light on the role played by epistatic selection in the dynamics of the allele substitutions responsible for reproductive barriers between species.

Evidence for complex genic interactions between conspecific chromosomes underlying hybrid female sterility in the Drosophila simulans clade

F1 hybrid females between the sibling species Drosophila simulans, Drosophila mauritiana and Drosophila sechellia are completely fertile. However, we have found that female sterility can be observed in F2 backcross females who are homozygous for D. simulans X chromosomes and homozygous for autosomal regions from either D. mauritiana or D. sechellia. Our results indicate that neither D. mauritiana autosome (2 or 3) can cause complete female sterility in a D. simulans background. The simultaneous presence of homozygous regions from both the second and third chromosomes of D. mauritiana, however, causes nearly complete female sterility which cannot be accounted for by their individual effects. The two autosomes of D. sechellia may show a similar pattern. From the same crosses, we also obtained evidence against a role for cytoplasmic or maternal effects in causing hybrid male sterility between these species. Taken with the results presented elsewhere, these observations suggest that epistatic interactions between conspecific genes in a hybrid background may be the prevalent mode of hybrid sterility between recently diverged species.

Genetics of reproductive isolation in the Drosophila simulans clade: complex epistasis underlying hybrid male sterility

We have analyzed the sterility associated with introgressions of the distal one-fourth of the X chromosome from either Drosophila mauritiana or Drosophila sechellia into the genome of Drosophila simulans using a series of visible and DNA markers. Because in Drosophila hybrids, male sterility is usually complete and is often tightly linked with each of several markers used in crosses, a simple genetic basis has generally been assumed. In our low resolution mapping experiment, we were not able to reject the null hypothesis that a single gene, introgressed from either D. mauritiana or D. sechellia, is the cause of male sterility. High resolution mapping, however, reveals a much more complex picture. At least three distinct factors from D. mauritiana, or two from D. sechellia, were identified that need to be jointly present to confer full sterility. Each individual factor by itself is relatively ineffective in causing sterility, or even a partial spermatogenic defect. Moreover, there appear to be more sterility factors on comparable introgressions from D. mauritiana than from D. sechellia. On the basis of these observations, we propose a model which suggests that multilocus weak allele interactions are a very common cause of reproductive incompatibility between closely related species. We also present theoretical argument and empirical evidence against extrapolating the results of within-species analysis to interpret the genetic basis of species differences. The implications of this model on the theories of evolution of species differences and the attempt to understand the mechanisms of hybrid sterility/inviability at the molecular level are discussed.

Characterization of two Segregation distorter revertants: evidence that the tandem duplication is necessary for Sd activity in Drosophila melanogaster

Segregation Distorter (SD) is a naturally occurring system of meiotic drive in Drosophila melanogaster. Males heterozygous for an SD second chromosome and a normal homolog (SD+) transmit predominantly SD-bearing sperm. To accomplish this, the Segregation distorter (Sd) locus induces the dysfunction of those spermatids that receive the SD+ chromosome. Recently, P. A. Powers and B. Ganetzky isolated overlapping DNA clones spanning the region of DNA known to contain the Sd gene and identified a 5-kb tandem duplication that is present on all SD chromosomes examined, but is apparently absent from wild-type chromosomes. Here we report a molecular analysis of two spontaneous revertants from an Australian SD chromosome (SD-Arm28). Both of these revertants have lost the 5-kb tandem duplication along with the ability to distort transmission; the critical observation, however, is that they retain the DNA haplotype in the flanking regions (both proximally and distally) that is characteristic of the original SD-Arm28. We propose unequal sister chromatid exchange between the tandem repeats as the only plausible explanation for loss of a repeat while retaining flanking markers. This provides direct evidence that the tandem duplication is indeed necessary for the Sd phenotype. Further, we examined testes-specific levels of both RNA and protein for the nearby Topoisomerase 2 gene. Neither revealed a consistent difference between SD and SD+ strains. We also measured testes-specific levels of RNA using the tandem duplication itself as probe. Our results suggest that there is strong up-regulation of one or several 2.0-2.3-kb transcripts from the duplicated region in the testes of an SD strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Population genetics of tandem repeats in centromeric heterochromatin: unequal crossing over and chromosomal divergence at the Responder locus of Drosophila melanogaster

The Responder (Rsp) locus in Drosophila melanogaster is the target locus of segregation distortion and is known to be comprised of a tandem array of 120-bp repetitive sequences. In this study, we first determined the large scale molecular structure of the Rsp locus, which extends over a region of 600 kb on the standard sensitive (cn bw) chromosome. Within the region, small Rsp repeat arrays are interspersed with non-Rsp sequences and account for 10-20% of the total sequences. We isolated and sequenced 32 Rsp clones from three different chromosomes. The main results are: (1) Rsp repeats isolated from the same chromosome are not more similar than those from different chromosomes. This implies either that there are more homologous exchanges at the Rsp locus than expected or, alternatively, that the second chromosomes of D. melanogaster have diverged from one another more recently at the centromeric heterochromatin than at the nearby euchromatin. (2) The repeats usually have a dimeric structure with an average difference of 16% between the left and right halves. The differences allow us to easily identify the products of unequal exchanges. Despite the large differences between the two halves, exchanges have occurred frequently and the majority of them fall within a 29-bp interval of identity between the two halves. Our data thus support the suggestion that recombination depends on short stretches of complete identity rather than long stretches of general homology. (3) Frequent unequal crossover events obscure the phylogenetic relationships between repeats; therefore, different parts of any single repeat could often have different phylogenetic histories. The high rate of unequal crossing over may also help explain the evolutionary dynamics of the Rsp locus.