Tissue-specific cell lineages originate in the gastrula of the zebrafish

In the zebrafish, cells of a clone derived from a single blastomere migrate away from one another during gastrulation. Later in development their descendants are usually found scattered within several different types of tissues of embryo. The divisions and migrations of individual cells were monitored during early development, revealing that in most cases the lineal descendants of single cells present at gastrula stage exclusively populate only single tissues, and may have stereotyped positional relationships within these tissues. Thus the gastrula stage is the first stage when heritable restrictions in cell type might arise in the zebrafish.     

An inherited functional circadian clock in zebrafish embryos

Circadian clocks are time-keeping systems found in most organisms. In zebrafish, expression of the clock gene Period3 (Per3) oscillates throughout embryogenesis in the central nervous system and the retina. Per3 rhythmic expression was free-running and was reset by light but not by the developmental delays caused by low temperature. The time of fertilization had no effect on Per3 expression. Per3 messenger RNA accumulates rhythmically in oocytes and persists in embryos. Our results establish that the circadian clock functions during early embryogenesis in zebrafish. Inheritance of maternal clock gene products suggests a mechanism of phase inheritance through ovogenesis.     

莠去津和芴对斑马鱼胚胎的联合毒性效应研究

为了研究莠去津和芴的联合毒性效应,以斑马鱼作为模式生物,进行胚胎发育暴露实验、联合毒性模型预测和靶向氨基酸代谢组学研究。结果表明,在联合暴露120 h后的斑马鱼仔鱼中均观察到异常发育情况,会引起斑马鱼胚胎卵黄囊异常和脊柱弯曲,其毒性作用方式分别为拮抗作用和协同作用,且无论低高剂量下,二元联合暴露比单一暴露时毒性风险更高。靶向代谢组学研究发现,污染物主要通过干扰甘氨酸、丝氨酸、苏氨酸和组氨酸代谢等途径影响斑马鱼仔鱼的氨基酸代谢。研究表明,莠去津和芴的联合暴露对斑马鱼胚胎的神经发育、氧化应激、抗炎机制、能量代谢、免疫和细胞凋亡机制等生理功能可能产生影响,进而影响其生长发育,且卵黄囊异常是较为敏感的毒性指标。     

灭多威对斑马鱼胚胎抗氧化防御系统的影响

为探究灭多威对斑马鱼胚胎抗氧化防御系统的影响及氧化损伤效应,将受精后6h内的斑马鱼胚胎暴露在浓度为0、2、20、200 μg·L^-1的灭多威溶液中,分别在24、48、72、96h时测定斑马鱼体内超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、谷胱甘肽还原酶（GR）、还原型谷胱甘肽（GSH）、氧化型谷胱甘肽（GSSG）的活性及丙二醛（MDA）的含量。暴露于灭多威后,SOD活性呈现先降低后升高再降低的趋势,各浓度处理组与对照组差异显著（P<0.05）;CAT活性表现为先被诱导后抑制减弱的效应,其中20、200μg·L^-1处理组CAT活性显著高于对照组（P<0.05）;GR、GSH、GSSG活性呈现先升高后降低的趋势;与对照组相比,各浓度处理组斑马鱼胚胎体内MDA含量增加,呈先增加后减少再增加的趋势。灭多威对斑马鱼胚胎具氧化应激效应,造成鱼体内抗氧化防御因子活性水平及MDA含量发生改变,干扰抗氧化防御系统正常工作,具有氧化损伤效应。     

Heart regeneration in zebrafish

Cardiac injury in mammals and amphibians typically leads to scarring, with minimal regeneration of heart muscle. Here, we demonstrate histologically that zebrafish fully regenerate hearts within 2 months of 20% ventricular resection. Regeneration occurs through robust proliferation of cardiomyocytes localized at the leading epicardial edge of the new myocardium. The hearts of zebrafish with mutations in the Mps1 mitotic checkpoint kinase, a critical cell cycle regulator, failed to regenerate and formed scars. Thus, injury-induced cardiomyocyte proliferation in zebrafish can overcome scar formation, allowing cardiac muscle regeneration. These findings indicate that zebrafish will be useful for genetically dissecting the molecular mechanisms of cardiac regeneration.     

Widespread origins of domestic horse lineages

Domestication entails control of wild species and is generally regarded as a complex process confined to a restricted area and culture. Previous DNA sequence analyses of several domestic species have suggested only a limited number of origination events. We analyzed mitochondrial DNA (mtDNA) control region sequences of 191 domestic horses and found a high diversity of matrilines. Sequence analysis of equids from archaeological sites and late Pleistocene deposits showed that this diversity was not due to an accelerated mutation rate or an ancient domestication event. Consequently, high mtDNA sequence diversity of horses implies an unprecedented and widespread integration of matrilines and an extensive utilization and taming of wild horses. However, genetic variation at nuclear markers is partitioned among horse breeds and may reflect sex-biased dispersal and breeding.     

MicroRNA expression in zebrafish embryonic development

MicroRNAs (miRNAs) are small noncoding RNAs, about 21 nucleotides in length, that can regulate gene expression by base-pairing to partially complementary mRNAs. Regulation by miRNAs can play essential roles in embryonic development. We determined the temporal and spatial expression patterns of 115 conserved vertebrate miRNAs in zebrafish embryos by microarrays and by in situ hybridizations, using locked-nucleic acid-modified oligonucleotide probes. Most miRNAs were expressed in a highly tissue-specific manner during segmentation and later stages, but not early in development, which suggests that their role is not in tissue fate establishment but in differentiation or maintenance of tissue identity.     

FGF-dependent mechanosensory organ patterning in zebrafish

During development, organ primordia reorganize to form repeated functional units. In zebrafish (Danio rerio), mechanosensory organs called neuromasts are deposited at regular intervals by the migrating posterior lateral line (pLL) primordium. The pLL primordium is organized into polarized rosettes representing proto-neuromasts, each with a central atoh1a-positive focus of mechanosensory precursors. We show that rosettes form cyclically from a progenitor pool at the leading zone of the primordium as neuromasts are deposited from the trailing region. fgf3/10 signals localized to the leading zone are required for rosette formation, atoh1a expression, and primordium migration. We propose that the fibroblast growth factor (FGF) source controls primordium organization, which, in turn, regulates the periodicity of neuromast deposition. This previously unrecognized mechanism may be applicable to understanding segmentation and morphogenesis in other organ systems.     

Seasonal dynamics of previously unknown fungal lineages in tundra soils

The finding that microbial communities are active under snow has changed the estimated global rates of biogeochemical processes beneath seasonal snow packs. We used microbiological and molecular techniques to elucidate the phylogenetic composition of undersnow microbial communities in Colorado, the United States. Here, we show that tundra soil microbial biomass reaches its annual peak under snow, and that fungi account for most of the biomass. Phylogenetic analysis of tundra soil fungi revealed a high diversity of fungi and three novel clades that constitute major new groups of fungi (divergent at the subphylum or class level). An abundance of previously unknown fungi that are active beneath the snow substantially broadens our understanding of both the diversity and biogeochemical functioning of fungi in cold environments.     

Melatonin suppresses nighttime memory formation in zebrafish

Memory processes are modulated by the biological clock, although the mechanisms are unknown. Here, we report that in the diurnal zebrafish both learning and memory formation of an operant conditioning paradigm occur better during the day than during the night. Melatonin treatment during the day mimics the nighttime suppression of memory formation. Training in constant light improves nighttime memory formation while reducing endogenous melatonin concentrations. Treatment with melatonin receptor antagonists at night dramatically improves memory. Pinealectomy also significantly improves nighttime memory formation. We adduce that melatonin is both sufficient and necessary for poor memory formation during the night.     

Myc-induced T cell leukemia in transgenic zebrafish

The zebrafish is an attractive model organism for studying cancer development because of its genetic accessibility. Here we describe the induction of clonally derived T cell acute lymphoblastic leukemia in transgenic zebrafish expressing mouse c-myc under control of the zebrafish Rag2 promoter. Visualization of leukemic cells expressing a chimeric transgene encoding Myc fused to green fluorescent protein (GFP) revealed that leukemias arose in the thymus, spread locally into gill arches and retro-orbital soft tissue, and then disseminated into skeletal muscle and abdominal organs. Leukemic cells homed back to the thymus in irradiated fish transplanted with GFP-labeled leukemic lymphoblasts. This transgenic model provides a platform for drug screens and for genetic screens aimed at identifying mutations that suppress or enhance c-myc- induced carcinogenesis.