Coevolutionary Interactions between Sexual and Habitat Isolation during Reinforcement.

Speciation often involves the evolution of multiple genetic-based barriers to gene flow (i.e., "coupling"). However, barriers may exhibit a diversity of evolutionary interactions during speciation. These dynamics are important in reinforcement, where selection may favor different prezygotic isolating barriers to avoid maladaptive hybridization. Here we study the interaction between evolution of sexual and habitat isolation. We first review the empirical literature where both barriers were explicitly considered, and then develop a population genetic model of reinforcement. Most studies of both sexual and habitat isolation were found in phytophagous insect systems. In 76% of these studies, both barriers coevolved; the remaining cases either showed only habitat isolation (21%) or only sexual isolation (3%). Our two-allele genetic mechanism model of each barrier also found that these often coevolved, but habitat isolation was generally more effective during reinforcement. Depending on the fitness of hybrids (e.g., Dobzhansky-Muller incompatibilities) and initial migration rate, these barriers could either facilitate, curtail, or have no effect on each other. This indicates that basic parameters will alter the underlying evolutionary dynamics, and thus the nature of "speciation coupling" will be highly variable in natural systems. Finally, we studied initially asymmetrical migration rates and found that populations with higher initial emigration evolved stronger habitat isolation, while populations that initially received more immigrants exhibited stronger sexual isolation. These results are in line with observations in some empirical studies, but more data is needed to test their generality.

Evolution of choosiness dictates whether search costs of mate choice enhance speciation by sexual selection.

The role of sexual selection in speciation is implicated in both empirical case studies and larger comparative works. However, sexual selection faces two major problems in driving speciation. First, because females with novel preferences search for their initially rare males, search costs are expected to curtail initial sexual divergence. Second, if these populations come back into sympatry, sexual divergence may be erased due to hybridization. A major goal is to understand which conditions increase the likelihood of overcoming these problems. Here we generated a diploid population genetic model of how female search costs and evolution of female 'choosiness' (i.e. preference strength) interact to drive speciation in allopatry and secondary contact. We studied the model using numerical simulations in the context of two different male traits, ecologically 'arbitrary' versus 'magic' traits. First, in allopatry, without female search costs only minor and fluctuating sexual isolation evolved. In contrast, with female search costs, sexual isolation was highly curtailed with arbitrary male traits but was greatly facilitated with magic traits. However, because search costs selected for reduced choosiness, sexual isolation with magic traits was eventually eroded, the rate determined by the genetic architecture of choosiness. These factors also played a key role in secondary contact; with evolvable choosiness and female search costs, pure sexual selection models collapsed upon secondary contact. However, when we added selection against hybrids (i.e. reinforcement) to this model, we found that speciation could be maintained under a wide range of conditions with arbitrary male traits, but not with magic male traits. This surprisingly suggests that arbitrary male traits are in some cases more likely to aid speciation than magic male traits. We discuss these findings and relate them to empirical literature on female choosiness within species and in hybrids.

Is cascade reinforcement likely when sympatric and allopatric populations exchange migrants?

When partially reproductively isolated species come back into secondary contact, these taxa may diverge in mating preferences and sexual cues to avoid maladaptive hybridization, a process known as reinforcement. This phenomenon often leads to reproductive character displacement (RCD) between sympatric and allopatric populations of reinforcing species that differ in their exposure to hybridization. Recent discussions have reinvigorated the idea that RCD may give rise to additional speciation between conspecific sympatric and allopatric populations, dubbing the concept "cascade reinforcement." Despite some empirical studies supporting cascade reinforcement, we still know very little about the conditions for its evolution. In the present article, we address this question by developing an individual-based population genetic model that explicitly simulates cascade reinforcement when one of the hybridizing species is split into sympatric and allopatric populations. Our results show that when sympatric and allopatric populations reside in the same environment and only differ in their exposure to maladaptive hybridization, migration between them generally inhibits the evolution of cascade by spreading the reinforcement alleles from sympatry into allopatry and erasing RCD. Under these conditions, cascade reinforcement only evolved when migration rate between sympatric and allopatric populations was very low. This indicates that stabilizing sexual selection in allopatry is generally ineffective in preventing the spread of reinforcement alleles. Only when sympatric and allopatric populations experienced divergent ecological selection did cascade reinforcement evolve in the presence of substantial migration. These predictions clarify the conditions for cascade reinforcement and facilitate our understanding of existing cases in nature.

Patterns and processes of genome-wide divergence between North American and African Drosophila melanogaster.

Genomic tools and analyses are now being widely used to understand genome-wide patterns and processes associated with speciation and adaptation. In this article, we apply a genomics approach to the model organism Drosophila melanogaster. This species originated in Africa and subsequently spread and adapted to temperate environments of Eurasia and the New World, leading some populations to evolve reproductive isolation, especially between cosmopolitan and Zimbabwean populations. We used tiling arrays to identify highly differentiated regions within and between North America (the United States and Caribbean) and Africa (Cameroon and Zimbabwe) across 63% of the D. melanogaster genome and then sequenced representative fragments to study their genetic divergence. Consistent with previous findings, our results showed that most differentiation was between populations living in Africa vs. outside of Africa (i.e., "out-of-Africa" divergence), with all other geographic differences being less substantial (e.g., between cosmopolitan and Zimbabwean races). The X chromosome was much more strongly differentiated than the autosomes between North American and African populations (i.e., greater X divergence). Overall differentiation was positively associated with recombination rates across chromosomes, with a sharp reduction in regions near centromeres. Fragments surrounding these high F(ST) sites showed reduced haplotype diversity and increased frequency of rare and derived alleles in North American populations compared to African populations. Nevertheless, despite sharp deviation from neutrality in North American strains, a small set of bottleneck/expansion demographic models was consistent with patterns of variation at the majority of our high F(ST) fragments. Although North American populations were more genetically variable compared to Europe, our simulation results were generally consistent with those previously based on European samples. These findings support the hypothesis that most differentiation between North America and Africa was likely driven by the sorting of African standing genetic variation into the New World via Europe. Finally, a few exceptional loci were identified, highlighting the need to use an appropriate demographic null model to identify possible cases of selective sweeps in species with complex demographic histories.

A novel method, digital genome scanning detects KRAS gene amplification in gastric cancers: involvement of overexpressed wild-type KRAS in downstream signaling and cancer cell growth.

BACKGROUND: Gastric cancer is the third most common malignancy affecting the general population worldwide. Aberrant activation of KRAS is a key factor in the development of many types of tumor, however, oncogenic mutations of KRAS are infrequent in gastric cancer. We have developed a novel quantitative method of analysis of DNA copy number, termed digital genome scanning (DGS), which is based on the enumeration of short restriction fragments, and does not involve PCR or hybridization. In the current study, we used DGS to survey copy-number alterations in gastric cancer cells. METHODS: DGS of gastric cancer cell lines was performed using the sequences of 5000 to 15000 restriction fragments. We screened 20 gastric cancer cell lines and 86 primary gastric tumors for KRAS amplification by quantitative PCR, and investigated KRAS amplification at the DNA, mRNA and protein levels by mutational analysis, real-time PCR, immunoblot analysis, GTP-RAS pull-down assay and immunohistochemical analysis. The effect of KRAS knock-down on the activation of p44/42 MAP kinase and AKT and on cell growth were examined by immunoblot and colorimetric assay, respectively. RESULTS: DGS analysis of the HSC45 gastric cancer cell line revealed the amplification of a 500-kb region on chromosome 12p12.1, which contains the KRAS gene locus. Amplification of the KRAS locus was detected in 15% (3/20) of gastric cancer cell lines (8-18-fold amplification) and 4.7% (4/86) of primary gastric tumors (8-50-fold amplification). KRAS mutations were identified in two of the three cell lines in which KRAS was amplified, but were not detected in any of the primary tumors. Overexpression of KRAS protein correlated directly with increased KRAS copy number. The level of GTP-bound KRAS was elevated following serum stimulation in cells with amplified wild-type KRAS, but not in cells with amplified mutant KRAS. Knock-down of KRAS in gastric cancer cells that carried amplified wild-type KRAS resulted in the inhibition of cell growth and suppression of p44/42 MAP kinase and AKT activity. CONCLUSION: Our study highlights the utility of DGS for identification of copy-number alterations. Using DGS, we identified KRAS as a gene that is amplified in human gastric cancer. We demonstrated that gene amplification likely forms the molecular basis of overactivation of KRAS in gastric cancer. Additional studies using a larger cohort of gastric cancer specimens are required to determine the diagnostic and therapeutic implications of KRAS amplification and overexpression.

Retroperitoneal mixed-type liposarcoma showing features of four different subtypes.

Mixed-type liposarcoma is a rare soft tissue tumor. This report describes a 50-year-old man with retroperitoneal mixed-type liposarcoma that consisted of four pathologically different components. Preoperative CT and MRI showed a giant retroperitoneal mass composed of several nodules with various attenuation and signal intensity. At laparotomy, the tumor appeared to be composed of four components. Pathologic examination revealed that each component was of a histologically different subtype. Mixed-type liposarcoma containing four different subtypes is extremely rare. Its clinical and pathologic features are briefly reviewed.

Long-term adaptation of epistatic genetic networks.

Gene networks are likely to govern most traits in nature. Mutations at these genes often show functional epistatic interactions that lead to complex genetic architectures and variable fitness effects in different genetic backgrounds. Understanding how epistatic genetic systems evolve in nature remains one of the great challenges in evolutionary biology. Here we combine an analytical framework with individual-based simulations to generate novel predictions about long-term adaptation of epistatic networks. We find that relative to traits governed by independently evolving genes, adaptation with epistatic gene networks is often characterized by longer waiting times to selective sweeps, lower standing genetic variation, and larger fitness effects of adaptive mutations. This may cause epistatic networks to either adapt more slowly or more quickly relative to a nonepistatic system. Interestingly, epistatic networks may adapt faster even when epistatic effects of mutations are on average deleterious. Further, we study the evolution of epistatic properties of adaptive mutations in gene networks. Our results show that adaptive mutations with small fitness effects typically evolve positive synergistic interactions, whereas adaptive mutations with large fitness effects evolve positive synergistic and negative antagonistic interactions at approximately equal frequencies. These results provide testable predictions for adaptation of traits governed by epistatic networks and the evolution of epistasis within networks.

Isolated periportal tuberculosis: characteristic findings of clinical imaging.

Isolated periportal tuberculous lymphadenopathy is a rare clinical entity. This report describes a 56-year-old woman with the disease, who showed characteristic findings on clinical imaging studies. Computed tomography showed a low-density mass with peripheral enhancement and calcification, adjacent to the pancreatic head and caudate lobe of the liver. 2-[Fluorine 18]fluoro-2-deoxy-D-glucose positron emission tomography imaging co-registered with computed tomography showed slightly increased uptake along the periphery of the lesion. The diagnosis was confirmed at laparotomy. The manifestation of the disease is nonspecific, and preoperative differential diagnosis from neoplastic disease is often difficult. Its clinical and radiological features are briefly reviewed.

Pseudomyxoma peritonei presenting with femoral hernias and peritonitis.

Pseudomyxoma peritonei is a rare disease characterized by intraperitoneal accumulation of mucinous ascites produced by neoplastic cells, which mostly originate from an appendiceal adenoma. The clinical presentation of the disease varies, and preoperative diagnosis is often difficult. This report describes a 76-year-old female patient with pseudomyxoma peritonei who presented with lower abdominal pain and bilateral femoral masses. Computed tomography revealed bilateral femoral hernias and fluid collection in the peritoneal cavity. Laparotomy was performed, during which we found extensive diffuse gelatinous material mixed with purulent ascites, and the diagnosis of pseudomyxoma peritonei was confirmed. The disease is rarely associated with femoral hernias or peritonitis. Its clinical presentation, including the characteristic findings on computed tomography, and surgical management are briefly reviewed.

Comparative genome analysis identifies the vitamin D receptor gene as a direct target of p53-mediated transcriptional activation.

p53 is the most frequently mutated tumor suppressor gene in human neoplasia and encodes a transcriptional coactivator. Identification of p53 target genes is therefore key to understanding the role of p53 in tumorigenesis. To identify novel p53 target genes, we first used a comparative genomics approach to identify p53 binding sequences conserved in the human and mouse genome. We hypothesized that potential p53 binding sequences that are conserved are more likely to be functional. Using stringent filtering procedures, 32 genes were newly identified as putative p53 targets, and their responsiveness to p53 in human cancer cells was confirmed by reverse transcription-PCR and real-time PCR. Among them, we focused on the vitamin D receptor (VDR) gene because vitamin D3 has recently been used for chemoprevention of human tumors. VDR is induced by p53 as well as several other p53 family members, and analysis of chromatin immunoprecipitation showed that p53 protein binds to conserved intronic sequences of the VDR gene in vivo. Introduction of VDR into cells resulted in induction of several genes known to be p53 targets and suppression of colorectal cancer cell growth. In addition, p53 induced VDR target genes in a vitamin D3-dependent manner. Our in silico approach is a powerful method for identification of functional p53 binding sites and p53 target genes that are conserved among humans and other organisms and for further understanding the function of p53 in tumorigenesis.

Genetic, epigenetic, and clinicopathologic features of gastric carcinomas with the CpG island methylator phenotype and an association with Epstein-Barr virus.

BACKGROUND: The CpG island methylator phenotype (CIMP), which is characterized by simultaneous methylation of the CpG islands of multiple genes, has been recognized as one of the important mechanisms in gastrointestinal carcinogenesis. METHODS: Methylation of the 5 methylated-in-tumors (MINT) loci and 12 tumor-related genes in 78 primary gastric carcinomas was examined using combined bisulfite-restriction analysis. Epstein-Barr virus (EBV)-associated gastric tumors were detected using real-time polymerase chain reaction analysis followed by an evaluation of the correlations between CIMP status, EBV-association, and genetic alteration of p53 and K-ras. The authors compared the clinicopathologic features of gastric carcinomas that had high CIMP methylation (CIMP-H) with tumors that had low CIMP methylation (CIMP-L) or negative CIMP methylation (CIMP-N). RESULTS: The methylation profiles of 12 genes showed nonrandom methylation, supporting the presence of CIMP in gastric carcinoma. No p53 mutations were detected among CIMP-H tumors, and no EBV association was detected in tumors that showed mutation of p53 and K-ras. In a multiple logistic regression model with CIMP-H as the dependent variable, proximal location (P = .011), diffuse type (P = .019), and less advanced pathologic TNM status (P = .043) contributed significantly to CIMP-H. Patients who had CIMP-N gastric tumors had a significantly worse survival than patients who had CIMP-H tumors (P = .004) or CIMP-L tumors (P = .012). EBV-associated tumors were associated strongly with CIMP-H, hypermethylation of tumor-related genes, and no p53 or K-ras mutation. CONCLUSIONS: CIMP status appeared to be associated with distinct genetic, epigenetic, and clinicopathologic features in gastric carcinomas. The finding that gastric carcinomas arose through different molecular pathways may affect not only tumor characteristics but also patient prognosis.

[A case of multiple hepatic and peritoneal metastases from colon cancer responding to oral UFT+leucovorin chemotherapy].

A 57-year-old woman underwent right hemicolectomy (D3) due to transverse colon cancer with multiple liver and peritoneal metastasis. Administration of oral UFT+Leucovorin was started postoperatively. After 6 months, the multiple liver metastases completely disappeared without any adverse reaction. After 14 months, no other recurrence was found by CT scan. This case suggests the usefulness of oral UFT+Leucovorin for progressive recurrent colorectal cancer as home chemotherapy.

Accuracy of linear-array EUS for preoperative staging of gastric cardia cancer.

BACKGROUND: The feasibility of a less invasive operation for early stage cancer of the gastric cardia with a low frequency of lymph node involvement has been previously demonstrated by us. Precise discrimination among mucosal, submucosal, and advanced cancers, as well as accurate evaluation of the proximal tumor margin are prerequisites for such stage-specific treatment. EUS is considered the most reliable staging modality. However, there is no EUS study specifically of cardia cancer. METHODS: Forty-five patients with gastric cardia cancer who underwent gastrectomy with at least first-tier lymphadenectomy were retrospectively analyzed. The results of preoperative linear-array echoendoscopy (7.5 MHz) with respect to cancer depth, lymph node involvement, and esophageal invasion were compared with postoperative histopathologic findings. RESULTS: Overall diagnostic accuracy for depth of invasion was 71%. Sensitivity for T1, T2, and T3 lesions was 100%, 31% and 75%, respectively. Overstaging of T2 cancers was the main diagnostic error. Mucosal (pT1-m) and submucosal (pT1-sm) cancers were correctly discriminated in 81% of patients. Diagnostic accuracy for lymph node involvement was 80%. EUS had positive and negative predictive values of 90% and 80%, respectively, for esophageal invasion. CONCLUSIONS: For gastric cardia cancer, the linear-array echoendoscope yielded satisfactory results with respect to depth of invasion, lymph node involvement, and esophageal invasion evaluation. The information obtained is useful to the performance of stage-specific treatment.

Gastric cancer with metastasis to the gingiva.

The present case report describes a gastric cancer which showed unusual metastasis in the oral region. A 56-year-old male patient underwent total gastrectomy and splenectomy due to advanced gastric cancer in the upper third of the stomach. Fifteen months later, he presented with anorexia and gingival swelling of durations of approximately 3 and 1 month, respectively. The gastric tumor was histologically a signet ring cell and a poorly differentiated cancer with a moderate degree of vascular invasion. Biopsy specimens from the gingival tumor revealed a signet ring cell cancer. Other metastatic sites were the brain, limb bones and abdominal lymph nodes. A bone scintigram revealed an abnormal uptake in the limb bones, while it did not exhibit any abnormality in the oral region. Correlation between the histology of the gingival tumor with that of the gastric cancer, as well as the absence of a gingival tumor at the time of prior gastrectomy, led to a diagnosis that the gingival tumor was a metastasis from gastric cancer. Gastric cancer metastasizing to the oral region, either the osseus or the oral soft tissue, is very rare. Although it cannot be proved without an autopsy, negative findings in the mandible by bone scanning in the present case suggest that direct gingival metastasis can be considered, rather than mandibular metastasis involving the gingiva. Hematogenous spread could be a mechanism of metastasis for this unusual tumor.

Activity and safety of a low dose, fractional administration of irinotecan hydrochloride (CPT-11) in combination with cisplatin for relapsed gastric cancer patients: a preliminary report.

BACKGROUND: Irinotecan hydrochloride (CPT-11) in combination with cisplatin has emerged as a new therapeutic option for the treatment of advanced gastric cancer. So far, very few combination trials have been reported, and a relatively high frequency of grade 3/4 toxicities in previous trials has been a major problem. The purpose of this study was to elucidate the efficacy and safety of a low dose, fractional administration of CPT-11 and cisplatin that is principally based on recently acquired knowledge of the synergistic antitumor activities between these two agents. METHODS: Five relapsed gastric cancer patients were treated every 2 weeks with a starting dose of CPT-11 (30 mg/m(2)) and a fixed dose of cisplatin (30 mg/m(2)). All patients were of performance status 0 and had received prior chemotherapy. Dose escalation of CPT-11 to 40 mg/m(2) or to 50 mg/m(2) was performed whenever possible. Responses, toxicities, and at-home ratio during chemotherapy were evaluated. RESULTS: The response rate reached 40%. Toxicities were grade 1/2, and no grade 3/4 hematological toxicities or diarrhea were observed. Repeated subsequent treatments could be performed in an outpatient setting without treatment delay or cancellations, which resulted in an 83%-92% at-home ratio in four patients receiving five or more cycles of treatment. There were no treatment-related deaths. CONCLUSION: A low dose, fractional administration of CPT-11 and cisplatin seems rational, encouraging, and safe, and compares well with other trials of the combination. Outpatient administration provides the patients with a better quality of life, suggesting a meaningful therapeutic option for relapsed gastric cancer patients in particular.