Usefulness of the G8 Geriatric Assessment Tool as a Prognostic Factor in Gemcitabine Plus Nab-paclitaxel Combination Therapy for Elderly Patients with Pancreatic Cancer.

Introduction: The usefulness of various prognostic factors for advanced pancreatic cancer (APC) has been reported, but the number of elderly patients in these studies is disproportionately fewer than those in general practice. This study aimed to examine the prognostic factors for elderly patients with APC receiving gemcitabine plus nab-paclitaxel (GnP) considering the G8 geriatric assessment tool. Methods: We retrospectively analyzed 77 elderly (≥65 years old) patients with APC who received GnP as first-line chemotherapy at our hospital. We used the receiver operating characteristic curve to set the optimal cutoff value for G8. Univariate and multivariate Cox regression models were applied to study independent prognostic factors. Results: The progression-free survival was 5.5 months, and the overall survival (OS) was 12.0 months in all patients. The most optimal cutoff of G8 was 10.5. OS of G8 ≥10.5 patients was superior to that of G8 <10.5 patients (18.5 versus 8.0 months). Multivariate analysis showed that Eastern Cooperative Oncology Group performance status 1 (hazard ratio [HR] 3.00, p = 0.02), neutrophil-lymphocyte ratio ≥3.9 (HR 2.73, p = 0.03), and G8 geriatric assessment <10.5 (HR 5.38, p < 0.001) were independent negative prognostic factors. Conclusions: G8 is useful for predicting prognoses in elderly patients with APC receiving GnP.

Asymptomatic Common Bile Duct Stones Are Associated with Increased Risk of Post-Endoscopic Retrograde Cholangiopancreatography Pancreatitis.

Introduction: Common bile duct stones (CBDS) are a common disease that can cause biliary complications, including cholangitis, obstructive jaundice, and biliary pancreatitis. Regardless of the presence or absence of symptoms, endoscopic removal of CBDS is generally recommended, but endoscopic retrograde cholangiopancreatography (ERCP) is a high-risk procedure with complications, such as post-ERCP pancreatitis (PEP). As few reports have addressed the risk of PEP by focusing on asymptomatic CBDS, the purpose of this study is to examine the incidence of PEP for asymptomatic CBDS. Methods: This retrospective study included data from 302 patients with naive papilla who underwent therapeutic ERCP for CBDS between January 2012 and December 2019 at our hospital. Univariate and multivariate logistic regression models were used to investigate independent risk factors for PEP. Results: Of the 302 patients, 32 were asymptomatic, and the remaining 270 were symptomatic. Five asymptomatic patients (15.6%) suffered from mild PEP, whereas 10 (3.7%) symptomatic patients suffered from PEP (9 were mild, and 1 was severe). Univariate analysis identified deep cannulation time more than 10 min, endoscopic papillary balloon dilation (EPBD), and asymptomatic CBDS as risk factors for PEP, whereas multivariate analysis revealed deep cannulation time more than 10 min (odds ratio (OR), 6.67; p < 0.001), EPBD (HR, 5.70; p < 0.001), and asymptomatic CBDS (HR, 5.49; p < 0.001) as independent risk factors for PEP. Conclusions: A wait-and-see approach may be an option for the management of asymptomatic CBDS. EPBD may be avoided, especially in case of asymptomatic or if difficult for bile duct cannulation.

Fracture of a Self-expandable Metallic Stent Inserted for Malignant Gastric Outlet Obstruction.

Duodenal stenting has gradually been established as the first-line treatment for malignant gastric outlet obstruction (GOO). We encountered a case of duodenal stent fracture in a 76-year-old woman with gastric cancer and GOO. She underwent self-expandable metallic stent (SEMS) placement. The SEMS was found to be fractured 4 weeks after its placement. We removed the broken part of the stent and placed a second SEMS. SEMS fracture is a rare and - to the best of our knowledge - unreported complication; hence, clinicians and their patients should be aware of this possibility.

Utility of the simplified measurements of muscle mass in patients with gastrointestinal and chronic liver diseases.

Sarcopenia is an important prognostic factor in patients with gastrointestinal and chronic liver diseases. Computed tomography and bioelectrical impedance analysis are the gold standards for measuring skeletal muscle mass for the diagnosis of decreased muscle mass, but there are some institutions where BIA and CT cannot be carried out. We evaluated the utility of simplified methods for measuring muscle mass; the psoas muscle mass index (PMI) method, simple PMI method, and arm muscle area (AMA) method. This retrospective study included 331 patients with gastrointestinal diseases and 81 patients with chronic liver diseases who were admitted from June 2018 to December 2019 at Municipal Hospital of Kofu. The skeletal muscle mass was measured using the PMI via the volume analyzer SYNAPSE VINCENT ver3.0, simple PMI based on CT imaging, and AMA method. Positive correlations were found between muscle mass measured by PMI and simple PMI, PMI and AMA, and simple PMI and AMA in patients with gastrointestinal diseases (correlation coefficients = 0.76, 0.57, 0.47, respectively, p < 0.001). Positive correlations were observed between muscle mass measured by PMI and simple PMI, PMI and AMA, and simple PMI and AMA in chronic liver diseases (correlation coefficients = 0.77, 0.53, 0.45, respectively, p < 0.001). Measurement of muscle mass by the AMA method showed some correlation with the PMI method. Measurement of muscle mass by the simple PMI method showed correlation with the PMI method. These simplified methods can be alternative methods of evaluating muscle mass in patients with gastrointestinal and chronic liver disease.

Relationship between presarcopenia and event occurrence in patients with primary hepatocellular carcinoma.

Presarcopenia is a prognostic factor in patients with hepatocellular carcinoma (HCC). The Japan integrated staging (JIS) score is a prognostic method that combines the Child-Turcotte-Pugh classification and the tumor-node-metastasis (TNM) staging for HCC. We investigated the relationship between presarcopenia, the JIS score, and prognosis in patients with primary HCC. This retrospective study included 153 patients with primary HCC who were hospitalized from October 2011 to March 2018 at Municipal Hospital of Kofu. The skeletal muscle mass was measured using simplified psoas muscle mass index (PMI) based on CT imaging, and PMI using the volume analyzer SYNAPSE VINCENT ver3.0. We diagnosed presarcopenia based on the cut off value according to the assessment criteria for sarcopenia in liver disease defined by the Japan Society of Hepatology. Forty-three patients (28%) were diagnosed with presarcopenia. The median event-free survival was significantly worse in patients with presarcopenia than those without presarcopenia (P = 0.016). In multivariate analysis, presence of presarcopenia, JIS score ≥3, alpha-fetoprotein ≥200 ng/ml, and prothrombin induced by vitamin K absence-II ≥ 200 mAU/ml were significant prognostic factors. Among the patients with JIS scores ≥3, there was no difference in the event occurrence rate with presence of presarcopenia (P = 0.96). Among the patients with JIS scores ≤2, the median event-free-survival was significantly shorter in those with presarcopenia than those without presarcopenia (P = 0.045). Presarcopenia was an independent prognostic factor in patients with primary HCC. In patients with JIS scores ≤2, the median event-free survival was significantly shorter in those with presarcopenia compared to those without presarcopenia. In the patients with JIS scores ≥3, there was no difference in the event occurrence rates in those with and without presarcopenia.

Extravasation and fluid collection on computed tomography imaging in patients with colonic diverticular bleeding.

OBJECTIVE: We evaluated the characteristics of patients with diverticular bleeding in whom emergency endoscopy should be proactively performed and those in whom it is unnecessary for spontaneous hemostasis following conservative treatment. METHODS: This study involved 132 patients in whom diverticular bleeding was diagnosed on lower gastrointestinal endoscopy. We evaluated the rate of identification of the bleeding diverticulum during endoscopy and the rate of spontaneous hemostasis following conservative treatment. RESULTS: In 26 patients (20%), bleeding diverticulum was identified during endoscopy. Extravasation or fluid collection on CT imaging was an important factor of successful identification of the bleeding source on endoscopy. Of the 104 patients in the conservative treatment group, 91 (87%) were able to be discharged after spontaneous hemostasis. Univariate analysis revealed a high rate of spontaneous hemostasis in patients without extravasation and fluid collection on CT imaging, those without adhesion of blood during endoscopy, those without diabetes, and those with a hemoglobin level ≥10 g/dL. CONCLUSION: In patients with colonic diverticular bleeding, extravasation or fluid collection on CT is an important factor related to the identification of the bleeding diverticulum. Patients without characteristic CT findings had a high rate of spontaneous hemostasis after conservative treatment. BACKGROUND: Diverticular bleeding is the most frequent cause of lower gastrointestinal bleeding accounting for 20%-40% of all cases in Japan and 20%-48% of all those in the Western countries[1, 2]. The prevalence of colonic diverticula tends to increase with age; thus, the overall prevalence of diverticular bleeding is expected to increase in the future. In Japan, the Japanese Gastroenterological Association published guidelines on colonic diverticulitis in 2017; these guidelines recommend the performance of lower gastrointestinal endoscopic examination within 24 h in patients with lower gastrointestinal bleeding suspected to be diverticular bleeding[3]. It has been reported that, for patients with lower gastrointestinal bleeding, urgent endoscopy helps avoid embolotherapy, colectomy, massive blood transfusion, and repeat bleeding[1, 4, 5]. However, it is often difficult to identify the bleeding point [6]; further, there are many challenging cases wherein it is difficult to decide whether urgent endoscopy should be performed in situations where there is insufficient medical staff, such as during nighttime and on holidays. Bleeding is reported to stop spontaneously with conservative treatment alone in 70% of diverticular bleeding cases[7, 8]. In particular, when determining the treatment policy for diverticular bleeding and in the case of patients at high risk of complications following endoscopy, such as older patients, those with poor performance status or cardiovascular disease, and those in whom spontaneous hemostasis can be expected, urgent endoscopy should be avoided, and elective endoscopy should be selected. Therefore, the type of cases wherein urgent endoscopy is effective and the type wherein it is unnecessary need to be clarified. Thus far, there have been very few reports of the characteristics of patients with diverticular bleeding in whom spontaneous hemostasis was achieved. We aimed to assess the characteristics of patients in whom emergency endoscopy should be proactively performed and those for whom it is unnecessary. Thus, we retrospectively analyzed the identification rate for the responsible diverticulum in patients with diverticular bleeding and the rate of spontaneous hemostasis following conservative treatment.

Comparative genomic and expression analysis of group B1 sox genes in zebrafish indicates their diversification during vertebrate evolution.

Group B1 Sox genes encode HMG domain transcription factors that play major roles in neural development. We have identified six zebrafish B1 sox genes, which include pan-vertebrate sox1a/b, sox2, and sox3, and also fish-specific sox19a/b. SOX19A/B proteins show a transcriptional activation potential that is similar to other B1 SOX proteins. The expression of sox19a and sox3 begins at approximately the 1,000-cell stage during embryogenesis and becomes confined to the future ectoderm by the shield stage. This is reminiscent of the epiblastic expression of Sox2 and/or Sox3 in amniotes. As development progresses, these six B1 sox genes display unique expression patterns that overlap distinctly from one region to another. sox19a expression is widespread in the early neuroectoderm, resembling pan-neural Sox2 expression in amniotes, whereas zebrafish sox2 shows anterior-restricted expression. Comparative genomics suggests that sox19a/b and mammalian Sox15 (group G) have an orthologous relationship and that the B1/G Sox genes arose from a common ancestral gene through two rounds of genome duplication. It seems likely, therefore, that each B1/G Sox gene has gained a distinct expression profile and function during vertebrate evolution.

A systematic genome-wide screen for mutations affecting organogenesis in Medaka, Oryzias latipes.

A large-scale mutagenesis screen was performed in Medaka to identify genes acting in diverse developmental processes. Mutations were identified in homozygous F3 progeny derived from ENU-treated founder males. In addition to the morphological inspection of live embryos, other approaches were used to detect abnormalities in organogenesis and in specific cellular processes, including germ cell migration, nerve tract formation, sensory organ differentiation and DNA repair. Among 2031 embryonic lethal mutations identified, 312 causing defects in organogenesis were selected for further analyses. From these, 126 mutations were characterized genetically and assigned to 105 genes. The similarity of the development of Medaka and zebrafish facilitated the comparison of mutant phenotypes, which indicated that many mutations in Medaka cause unique phenotypes so far unrecorded in zebrafish. Even when mutations of the two fish species cause a similar phenotype such as one-eyed-pinhead or parachute, more genes were found in Medaka than in zebrafish that produced the same phenotype when mutated. These observations suggest that many Medaka mutants represent new genes and, therefore, are important complements to the collection of zebrafish mutants that have proven so valuable for exploring genomic function in development.

Mutations affecting somite formation in the Medaka (Oryzias latipes).

The metameric structure of the vertebrate trunk is generated by repeated formation of somites from the unsegmented presomitic mesoderm (PSM). We report the initial characterization of nine different mutants affecting segmentation that were isolated in a large-scale mutagenesis screen in Medaka (Oryzias latipes). Four mutants were identified that show a complete or partial absence of somites or somite boundaries. In addition, five mutations were found that cause fused somites or somites with irregular sizes and shapes. In situ hybridization analysis using specific markers involved in the segmentation clock and antero-posterior (A-P) polarity of somites revealed that the nine mutants can be compiled into two groups. In group 1, mutants exhibit defects in tailbud formation and PSM prepatterning, whereas A-P identity in the somites is defective in group 2 mutants. Three mutants (planlos, pll; schnelles ende, sne; samidare, sam) have characteristic phenotypes that are similar to those in zebrafish mutants affected in the Delta/Notch signaling pathway. The majority of mutants, however, exhibit somitic phenotypes distinct from those found in zebrafish, such as individually fused somites and irregular somite sizes. Thus, these Medaka mutants can be expected to provide clues to uncovering novel components essential for somitogenesis.

Genetic dissection of the formation of the forebrain in Medaka, Oryzias latipes.

The forebrain, consisting of the telencephalon and diencephalon, is essential for processing sensory information. To genetically dissect formation of the forebrain in vertebrates, we carried out a systematic screen for mutations affecting morphogenesis of the forebrain in Medaka. Thirty-three mutations defining 25 genes affecting the morphological development of the forebrain were grouped into two classes. Class 1 mutants commonly showing a decrease in forebrain size, were further divided into subclasses 1A to 1D. Class 1A mutation (1 gene) caused an early defect evidenced by the lack of bf1 expression, Class 1B mutations (6 genes) patterning defects revealed by the aberrant expression of regional marker genes, Class 1C mutation (1 gene) a defect in a later stage, and Class 1D (3 genes) a midline defect analogous to the zebrafish one-eyed pinhead mutation. Class 2 mutations caused morphological abnormalities in the forebrain without considerably affecting its size, Class 2A mutations (6 genes) caused abnormalities in the development of the ventricle, Class 2B mutations (2 genes) severely affected the anterior commissure, and Class 2C (6 genes) mutations resulted in a unique forebrain morphology. Many of these mutants showed the compromised sonic hedgehog expression in the zona-limitans-intrathalamica (zli), arguing for the importance of this structure as a secondary signaling center. These mutants should provide important clues to the elucidation of the molecular mechanisms underlying forebrain development, and shed new light on phylogenically conserved and divergent functions in the developmental process.

Mutations affecting retina development in Medaka.

In a large scale mutagenesis screen of Medaka we identified 60 recessive zygotic mutations that affect retina development. Based on the onset and type of phenotypic abnormalities, the mutants were grouped into five categories: the first includes 11 mutants that are affected in neural plate and optic vesicle formation. The second group comprises 15 mutants that are impaired in optic vesicle growth. The third group includes 18 mutants that are affected in optic cup development. The fourth group contains 13 mutants with defects in retinal differentiation. 12 of these have smaller eyes, whereas one mutation results in enlarged eyes. The fifth group consists of three mutants with defects in retinal pigmentation. The collection of mutants will be used to address the molecular genetic mechanisms underlying vertebrate eye formation.

Mutations affecting retinotectal axonal pathfinding in Medaka, Oryzias latipes.

We screened for mutations affecting retinotectal axonal projection in Medaka, Oryzias latipes. In wild-type Medaka embryos, all the axons of retinal ganglion cells (RGCs) project to the contralateral tectum, such that the topological relationship of the retinal field is maintained. We labeled RGC axons using DiI/DiO at the nasodorsal and temporoventral positions of the retina, and screened for mutations affecting the pattern of stereotypic projections to the tectum. By screening 184 mutagenized haploid genomes, seven mutations in five genes causing defects in axonal pathfinding were identified, whereas mutations affecting the topographic projection of RGC axons were not found. The mutants were grouped into two classes according to their phenotypes. In mutants of Class I, a subpopulation of the RGC axons branched out either immediately after leaving the eye or after reaching the midline, and this axonal subpopulation projected to the ipsilateral tectum. In mutants of Class II, subpopulations of RGC axons branched out after crossing the midline and projected aberrantly. These mutants will provide clues to understanding the functions of genes essential for axonal pathfinding, which may be conserved or partly divergent among vertebrates.

Mutations affecting the formation of posterior lateral line system in Medaka, Oryzias latipes.

We performed a systematic screen for mutations affecting the trajectory of axons visualized by immunohistochemical staining of Medaka embryos with anti-acetylated tubulin antibody. Among the mutations identified, yanagi (yan) and kazura (kaz) mutations caused specific defects in projection of the posterior lateral line (PLL) nerve. In yan and kaz mutant embryos, the PLL nerve main bundle was misrouted ventrally and dorsally or anteriorly. Medaka semaphorin3A, sdf1, and cxcr4 cDNA fragments were cloned to allow analysis of these mutants. There were no changes in semaphorin3A or sdf1 expression in mutant embryos, suggesting that the tissues expressing semaphorin3A or sdf1 that are involved in PLL nerve guidance are present in these mutant embryos. Double staining revealed that the mislocated PLL primordium and growth cone of the ectopically projected PLL nerve were always colocalized in both yan and kaz mutant embryos, suggesting that migration of PLL primordia and PLL nerve growth cones are not uncoupled in these mutants. Although homozygous yan larvae showed incomplete migration of the PLL primordium along the anteroposterior axis, ventral proneuromast migration was complete, suggesting that ventral migration of the proneuromast does not require the signaling affected in yan mutants. In addition to the PLL system, the distribution of primordial germ cells (PGCs) was also affected in both yan and kaz mutant embryos, indicating that yan and kaz genes are required for the migration of both PLL primordia and PGCs. Genetic linkage analysis indicated that kaz is linked to cxcr4, but yan is not linked to sdf1 or cxcr4. These mutations will provide genetic clues to investigate the molecular mechanism underlying formation of the PLL system.

Mutations affecting thymus organogenesis in Medaka, Oryzias latipes.

The thymus is an organ for T lymphocyte maturation and is indispensable for the establishment of a highly developed immune system in vertebrates. In order to genetically dissect thymus organogenesis, we carried out a large-scale mutagenesis screening for Medaka mutations affecting recombination activating gene 1 (rag1) expression in the developing thymus. We identified 24 mutations, defining at least 13 genes, which led to a marked reduction of rag1 expression in the thymus. As thymus development depends on pharyngeal arches, we classified those mutations into three classes according to the defects in the pharyngeal arches. Class 1 mutants had no or slight morphological abnormalities in the pharyngeal arches, implying that the mutations may include defects in such thymus-specific events as lymphocyte development and thymic epithelial cell maturation. Class 2 mutants had abnormally shaped pharyngeal arches. Class 3 mutants showed severely attenuated pharyngeal arch development. In Class 2 and Class 3 mutants, the defects in thymus development may be due to abnormal pharyngeal arch development. Those mutations are expected to be useful for identifying the molecular mechanisms underlying thymus organogenesis.

Mutations affecting liver development and function in Medaka, Oryzias latipes, screened by multiple criteria.

We report here mutations affecting various aspects of liver development and function identified by multiple assays in a systematic mutagenesis screen in Medaka. The 22 identified recessive mutations assigned to 19 complementation groups fell into five phenotypic groups. Group 1, showing defective liver morphogenesis, comprises mutations in four genes, which may be involved in the regulation of growth or patterning of the gut endoderm. Group 2 comprises mutations in three genes that affect the laterality of the liver; in kendama mutants of this group, the laterality of the heart and liver is uncoupled and randomized. Group 3 includes mutations in three genes altering bile color, indicative of defects in hemoglobin-bilirubin metabolism and globin synthesis. Group 4 consists of mutations in three genes, characterized by a decrease in the accumulation of fluorescent metabolite of a phospholipase A(2) substrate, PED6, in the gall bladder. Lipid metabolism or the transport of lipid metabolites may be affected by these mutations. Mutations in Groups 3 and 4 may provide animal models for relevant human diseases. Group 5 mutations in six genes affect the formation of endoderm, endodermal rods and hepatic bud from which the liver develops. These Medaka mutations, identified by morphological and metabolite marker screens, should provide clues to understanding molecular mechanisms underlying formation of a functional liver.

Mutations affecting early distribution of primordial germ cells in Medaka (Oryzias latipes) embryo.

The development of germ cells has been intensively studied in Medaka (Oryzias latipes). We have undertaken a large-scale screen to identify mutations affecting the development of primordial germ cells (PGCs) in Medaka. Embryos derived from mutagenized founder fish were screened for an abnormal distribution or number of PGCs at embryonic stage 27 by RNA in situ hybridization for the Medaka vasa homologue (olvas). At this stage, PGCs coalesce into two bilateral vasa-expressing foci in the ventrolateral regions of the trunk after their migration and group organization. Nineteen mutations were identified from a screen corresponding to 450 mutagenized haploid genomes. Eleven of the mutations caused altered PGC distribution. Most of these alterations were associated with morphological abnormalities and could be grouped into four phenotypic classes: Class 1, PGCs dispersed into bilateral lines; Class 2, PGCs dispersed in a region more medial than that in Class 1; Class 3, PGCs scattered laterally and over the yolk sac area; and Class 4, PGCs clustered in a single median focus. Eight mutations caused a decrease in the number of PGCs. This decrease was observed in the offspring of heterozygous mothers, indicating the contribution of a maternal factor in determining PGC abundance. Taken together, these mutations should prove useful in identifying molecular mechanisms underlying the early PGC development and migration.

Mutations affecting gonadal development in Medaka, Oryzias latipes.

A gonad is formed from germ cells and somatic mesodermal cells through their interactions. Its development is coupled with the determination and differentiation of the sex and sex-associated traits. We carried out a large-scale screening of Medaka mutants in which gonadal development is affected. Screening was performed on larvae at 8 days posthatching for abnormal abundance and/or distribution of germ cells detected by the in situ hybridization for olvas (Medaka vasa). We describe here 16 mutants of 13 genes, which are classified into four groups. Group 1, consisting of four mutants of three genes kon, tot) characterised by an increase in germ cell number. An adult tot homozygote fish has the characteristic feature of possessing hypertrophic gonads filled with immature oocytes. Group 2, represented by a single gene (zen) mutant characterized by a gradual loss of germ cells. Group 3, consisting of four mutants of distinct genes (eko, eki, sht, ano) showing irregular clustering of germ cells. Group 4, consisting of seven mutants of five genes (arr, hyo, mzr, hdr, fbk) showing fragmented clusters of germ cells. In some mutants belonging to Groups 1, 3 and 4, the expression level of ftz-f1 (sf-1/Ad4BP) in gonadal somatic cells significantly decreased, suggesting that interaction between somatic and germ cells is affected.

Identification of radiation-sensitive mutants in the Medaka, Oryzias latipes.

We screened populations of N-ethyl-N-nitrosourea (ENU)-mutagenized Medaka, (Oryzias latipes) for radiation-sensitive mutants to investigate the mechanism of genome stability induced by ionizing radiation in developing embryos. F3 embryos derived from male founders that were homozygous for induced the mutations were irradiated with gamma-rays at the organogenesis stage (48hpf) at a dose that did not cause malformation in wild-type embryos. We screened 2130 F2 pairs and identified three types of mutants with high incidence of radiation-induced curly tailed (ric) malformations using a low dose of irradiation. The homozygous strain from one of these mutants, ric1, which is highly fertile and easy to breed, was established and characterized related to gamma-irradiation response. The ric1 strain also showed higher incidence of malformation and lower hatchability compared to the wild-type CAB strain after gamma-irradiation at the morula and pre-early gastrula stages. We found that the decrease in hatching success after gamma-irradiation, depends on the maternal genotype at the ric1 locus. Terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end-labeling assays showed a high frequency of apoptosis in the ric1 embryos immediately after gamma-irradiation at the pre-early gastrula stage but apoptotic cells were not observed before midblastula transition (MBT). The neutral comet assay revealed that the ric1 mutant has a defect in the rapid repair of DNA double-strand breaks induced by gamma-rays. These results suggest that RIC1 is involved in the DNA double strand break repair in embryos from morula to organogenesis stages, and unrepaired DNA double strand breaks in ric1 trigger apoptosis after MBT. These results support the use of the ric1 strain for investigating various biological consequences of DNA double strand breaks in vivo and for sensitive monitoring of genotoxicity related to low dose radiation.

Analysis of Wnt8 for neural posteriorizing factor by identifying Frizzled 8c and Frizzled 9 as functional receptors for Wnt8.

The dorsal ectoderm of vertebrate gastrula is first specified into anterior fate by an activation signal and posteriorized by a graded transforming signal, leading to the formation of forebrain, midbrain, hindbrain and spinal cord along the anteroposterior (A-P) axis. Transplanted non-axial mesoderm rather than axial mesoderm has an ability to transform prospective anterior neural tissue into more posterior fates in zebrafish. Wnt8 is a secreted factor that is expressed in non-axial mesoderm. To investigate whether Wnt8 is the neural posteriorizing factor that acts upon neuroectoderm, we first assigned Frizzled 8c and Frizzled 9 to be functional receptors for Wnt8. We then, transplanted non-axial mesoderm into the embryos in which Wnt8 signaling is cell-autonomously blocked by the dominant-negative form of Wnt8 receptors. Non-axial mesodermal transplants in embryos in which Wnt8 signaling is cell-autonomously blocked induced the posterior neural markers as efficiently as in wild-type embryos, suggesting that Wnt8 signaling is not required in neuroectoderm for posteriorization by non-axial mesoderm. Furthermore, Wnt8 signaling, detected by nuclear localization of beta-catenin, was not activated in the posterior neuroectoderm but confined in marginal non-axial mesoderm. Finally, ubiquitous over-expression of Wnt8 does not expand neural ectoderm of posterior character in the absence of mesoderm or Nodal-dependent co-factors. We thus conclude that other factors from non-axial mesoderm may be required for patterning neuroectoderm along the A-P axis.

An expression pattern screen for genes involved in the induction of the posterior nervous system of zebrafish.

The posterior nervous system, including the hindbrain and the spinal cord, has been shown to be formed by the transformation of neural plate of anterior character by signals derived from non-axial mesoderm. Although secreted factors, such as fibroblast growth factors (FGFs), Wnts, retinoic acid (RA) and Nodal, have been proposed to be the posteriorizing factors, the mechanism how neural tissue of posterior character is induced and subsequently specified along the anteroposterior axis remains elusive. To identify intercellular signaling molecules responsible for posteriorization of the neural plate as well as to find molecules induced intracellularly by the posteriorizing signal in the caudal neural plate, we screened by in situ hybridization for genes specifically expressed in posterior tissues, including the posterior neural plate and non-axial mesoderm when posteriorization of the neural plate takes place. From a subtracted library differentiating anterior versus posterior neural plate, 420 cDNA clones were tested, out of which 76 cDNA fragments showed expression restricted to the posterior tissue. These clones turned out to represent 32 different genes, including one novel secreted factor and one transmembrane protein. Seven genes were induced by non-axial mesodermal implants and bFGF beads, suggesting that these are among the early-response genes of the posteriorizing signal. Thus, our approach employing cDNA subtraction and subsequent expression pattern screening allows us to clone candidate genes involved in a novel signaling pathway contributing to the formation of the posterior nervous system.