Developmental Fate of Artificially Disordered Somite Cells after Heteroplastic Transplantation

A disordered somite pattern could be produced artificially when the segmental lateral plate of chickembryo was replaced by dissociated cells of quail segmental pate.The artificially disordered somitepattern formed at either place was used in our work as a model to analyze the mechanism of thedevelopment and differentiation of somite on chick embryo.Our conclusions include the following:1.Although the formation of somites from the dissociated segmental plate cells does not requirespecial environment,the development and differentiation of the somltes require a special environmentwhich is related to the neural tube and notochord.The effect of this special environmental factor maydecrease gradually with the increase of the distance from neural tube to lateral plate.2.The somites located on paraxial area at different distances to the axis have different fates indevelopment.3.The formation of epithelial vesicles is the property of somite cells and the epithelial vesicle is thestructural basis of somite differentiation.If and factor interferes with the differentiation of thesomite,the epithelial vesicle of the somite will be degenerated within certain period of time.4.During resegmentation of the somite,the number,size and arrangement of sclerotome in situ donot depend on the somite from which they are derived.5.Somite cells do not transdifferentiate into kidney tubule directly from their original epithelialvesicles,but are reorganized from the free cells dispersed from the disrupted somites.6.The establishment of cell commitment may involve several steps.Before commitment isestablished the of cell commitment is labile.7.The differentiation of sclerotome starts with the rupture of epithelial wall of somites and thedirection of its movement depends not only on the notochord but also on their position with respectto the neural tube and notochord.8.The disordered somite pattern doesn't influence the segmentation of dorsal root ganglia in situ,but causes the formation of the ectopic dorsal root ganglia.Key Words:Somite differentiation;Artificial disordered somite pattern;Chimeral somite;Resegmentation of sclerotome;Distribution of dorsal root ganglia     

Axial level-dependent differences in size of avian dorsal root ganglia are present from gangliogenesis

Dorsal root ganglia (DRG) form from neural crest cells that colonize the rostral sclerotomes of the somites of the trunk of higher vertebrates. Differences in sensory field size and innervation density are reflected by the size of the ganglia at different axial levels. Some of the position-dependent differences in ganglionic size derives from asymmetry in embryonic programmed cell death, when more DRG neurons die at non-limb-innervating levels than at the levels that innervate the limbs. I have now examined early chick embryos determine whether there is asymmetry in DRG size at the time of their condensation at stage 20 [embryonic day (E) 3], before the onset of cell death. Ganglia in brachial segments 14 and 15 are more than 80% larger on average than those in cervical segments 5 and 6 at this stage of development. This difference in volume is due to increased numbers of cells in the brachial sensory ganglia. Several other morphometric parameters of the DRG and sclerotomes were then determined. The rostro-caudal length was found to be significantly greater for brachial ganglia. The greater length of the brachial ganglia was found to be correlated with (1) a greater length of brachial than cervical sclerotomes and (2) the occupation by brachial ganglia of a larger proportion of the rostro-caudal extent of the sclerotome. These results demonstrate that the mature pattern of axial differences in ganglionic size are foreshadowed by a pattern set during the period of gangliogenesis, which is then further sculpted by apoptosis. This initial axial asymmetry in size preceding cell death parallels that recently shown for the development of the ventral motor column. Thus the sensory ganglia, like the somites, have distinct axial-position-dependent characteristics from their outset, characteristics that are not dependent on cell death resulting from competition for target-derived survival factors as was previously thought. DRG positional identities, like their segmentation, may be imposed by the paraxial mesoderm or may alternatively be intrinsically determined as is the case for the rhombomeres of the hindbrain. © 1993 John Wiley & Sons, Inc.     

Somitogenesis as a model to study the formation of morphological boundaries and cell epithelialization

The formation of morphological boundaries between developing tissues is an integral mechanism for generating body forms and functions. For the molecular and cellular studies of how such morphological boundaries form, somitogenesis serves as a particularly good model. When an intersomitic boundary forms in the anterior end of the presomitic mesoderm, cells undergo dynamic behaviors including a separation of tissues and changes in cell shape from mesenchymal to epithelial. Moreover, these events occur repeatedly and periodically. We here overview the inductive events that have recently been shown to play important roles in the formation of the intersomitic fissures. We then discuss molecular mechanisms underlying these inductive actions, and also discuss how the fissure formation is interpreted by the subsequent morphogenesis, including cell epithelialization and the acquisition of anterior–posterior identities in the newly formed somite. Thus, somitogenesis provides a unique model to understand how sequentially occurring processes of morphogenesis are coordinated in a 3-D environment.     

关于湖蛭属及其一新种的记述

我国原有鱼蛭科湖蛭属两种,其中中华湖蛭广泛分布华中地区,严重危害鲤、鲫鱼。据对安徽巢湖的调查,鲤鱼的感染率较鲫鱼高,大个体的感染率又较小个体的高。此蛭每年4月上旬开始离开鱼体到湖底繁殖,12月下旬新生幼体开始侵袭鱼体。哲罗湖蛭则仅限于黑龙江流域。1964年在青岛附近的黄海以及1975年在秦皇岛附近的渤海从两种硬骨鱼体上共得到4条属同一种的大型湖蛭,经鉴定为冈湖蛭Limnotrachelobdella okae,这是该种在我国首次记载。1985年在厦门附近的南海从赤点石斑鱼鳍上得到两条同属一种的小型湖蛭,被定为新种福建湖蛭(Limnotrachelobdella fujianensis sp.nov.)。本文给予此一新记录和一新种以详细的描述。       

Efficient embryonic culture method for the Japanese striped snake,Elaphe quadrivirgata,and its early developmental stages

The morphogenesis of snake embryos is an elusive yet fascinating research target for developmental biologists. However, few data exist on development of early snake embryo due to limited availability of pregnant snakes, and the need to harvest early stage embryos directly from pregnant snakes before oviposition without knowing the date of fertilization. We established an ex vivo culture method for early snake embryos using the Japanese striped snake, Elaphe quadrivirgata. This method, which we named “sausage‐style (SS) culture”, allows us to harvest snake embryos at specific stages for each experiment. Using this SS culture system, we calculated somite formation rate at early stages before oviposition. The average somite formation rate between 6/7 and 12/13 somite stages was 145.9 min, between 60/70 and 80/91 somite stages 42.4 min, and between 113–115 and 126/127 somite stages 71 min. Thus, somite formation rate that we observed during early snake embryogenesis was changed over time. We also describe a developmental staging series for E. quadrivirgata. This is the first report of a developmental series of early snake embryogenesis prior to oviposition by full‐color images with high‐resolution. We propose that the SS culture system is an easy method for treating early snake embryos ex vivo.     

A series of Cre‐ERT2 drivers for manipulation of the skeletal muscle lineage

We report the generation of five mouse strains with the tamoxifen‐inducible Cre (Cre‐ER^T2; CE) gene cassette knocked into the endogenous loci of Pax3, Myod1, Myog, Myf6, and Myl1, collectively as a resource for the skeletal muscle research community. We characterized these CE strains using the Cre reporter mice, R26R^LacZ, during embryogenesis and show that they direct tightly controlled tamoxifen‐inducible reporter expression within the expected cell lineage determined by each myogenic gene. We also examined a few selected adult skeletal muscle groups for tamoxifen‐inducible reporter expression. None of these new CE alleles direct reporter expression in the cardiac muscle. All these alleles follow the same knock‐in strategy by replacing the first exon of each gene with the CE cassette, rendering them null alleles of the endogenous gene. Advantages and disadvantages of this design are discussed. Although we describe potential immediate use of these strains, their utility likely extends beyond foreseeable questions in skeletal muscle biology. genesis 52:759–770, 2014. © 2014 Wiley Periodicals, Inc.     

Nestin-Cre transgenic mouse line Nes-Cre1 mediates highly efficient Cre/loxP mediated recombination in the nervous system, kidney, and somite-derived tissues

Here we describe the generation of the Nes-Cre1 transgenic mouse line in which Cre recombinase expression is controlled by the rat nestin promoter and intron 2 enhancer. This line has previously been used for conditional loss-of-function studies of various genes in the central nervous system and first branchial arch ectoderm. Here we report the detailed temporal and spatial recombination pattern of Nes-Cre1 using three different reporters of Cre-mediated recombination, ROSA26R (R26R), Z/AP, and Z/EG. Cre/loxP recombination was detected in embryos as early as the head-fold stage. By embryonic day (E)15.5 recombination occurred in virtually all cells of the nervous system and unexpectedly also in somite-derived tissues and kidneys. Tissues with little or no recombination included heart, liver, thymus, and lung. This study suggests that Nes-Cre1-mediated recombination occurs in progenitor cell types present in the neuroectoderm, the developing mesonephros, and the somites.     

Haplotype distribution in the GLI3 gene and their associations with growth traits in cattle

The glioma-associated oncogene family zinc finger 3 gene (GLI3) mediates in all vertebrates hedgehog (Hh) signaling that plays an essential role in the induction and patterning of numerous cell types during invertebrate and vertebrate development. In this study, a total of 6 single nucleotide polymorphisms (SNPs: 1–6) were identified by polymerase chain reaction–single stranded conformational polymorphism (PCR–SSCP) and DNA pool sequencing, including all 13 exons and 12 exon–intron boundaries within the bovine GLI3 gene. 16 haplotypes and 13 combined genotypes were revealed and the linkage disequilibrium was assessed in 708 individuals representing three main cattle breeds from China. The statistical analyses indicated that the SNP2, 3 and 4 are associated with the body weight at birth and 6 months in Nanyang cattle population (P < 0.05). No significant association was detected between 11 combined genotypes and body weight at five different ages. Our results provide evidence that polymorphisms in the GLI3 gene are associated with growth traits, and may be used for marker-assisted selection in beef cattle breeding program.     

The Notch-regulated ankyrin repeat protein is required for proper anterior-posterior somite patterning in mice

The Notch-regulated ankyrin repeat protein (Nrarp) is a component of a negative feedback system that attenuates Notch pathway-mediated signaling. In vertebrates, the timing and spacing of formation of the mesodermal somites are controlled by a molecular oscillator termed the segmentation clock. Somites are also patterned along the rostral-caudal axis of the embryo. Here, we demonstrate that Nrarp-deficient embryos and mice exhibit genetic background-dependent defects of the axial skeleton. While progression of the segmentation clock occurred in Nrarp-deficient embryos, they exhibited altered rostrocaudal patterning of the somites. In Nrarp mutant embryos, the posterior somite compartment was expanded. These studies confirm an anticipated, but previously undocumented role for the Nrarp gene in vertebrate somite patterning and provide an example of the strong influence that genetic background plays on the phenotypes exhibited by mutant mice.