Region-specific neural induction of an engrailed protein by anterior notochord in Xenopus

Anterior-specific neural induction can be assayed by means of an antibody that recognizes the Xenopus homeobox-containing protein En-2. The En-2 antigen is an excellent early marker, since it is present as a discrete band in the anterior neural plate of neurula embryos. Regional induction was assayed by combining dorsal mesoderm with competent ectoderm. Anterior notochord from the early neurula induced En-2 frequently, while posterior notochord induced En-2 less frequently. Presumptive somitic mesoderm and presumptive head mesoderm, though they induced neural tissue, were not strong inducers of En-2. Thus, anterior notochord may be the primary mesodermal tissue responsible for the patterning of the anterior neural plate.     

Protein kinase C and regulation of the local competence of Xenopus ectoderm

The limited competence of embryonic tissue to respond to an inductive signal has an essential, regulatory function in embryonic induction. The molecular basis for the competence of Xenopus ectoderm to differentiate into neural tissue was investigated. Dorsal mesoderm or 12-O-tetradecanoyl phorbol-13-acetate (TPA) caused in vivo activation of protein kinase C (PKC) and neural differentiation mainly in dorsal ectoderm and to a lesser extent in ventral ectoderm. These data correlate with the observations that PKC preparations from dorsal and ventral ectoderm differ, the dorsal PKC preparation being more susceptible to activation by TPA and diolein than is the ventral PKC preparation. Monoclonal antibodies against the bovine PKC alpha plus beta or gamma isozymes immunostained dorsal and ventral ectoderm, respectively, which suggests different localizations of PKC isozymes. These results suggest that PKC participates in the establishment of embryonic competence.     

Fetal alcohol syndrome: embryogenesis in a mouse model

When two small doses of ethanol were administered to pregnant mice during the gastrulation stage of embryogenesis, the embryos developed craniofacial malformations closely resembling those seen in the human fetal alcohol syndrome. Striking histological changes appeared in the developing brain (neuroectoderm) within 24 hours of exposure. Decreased development of the neural plate and its derivatives apparently accounts for the craniofacial malformations. The critical exposure period is equivalent to the third week in human pregnancy.     

壶瓶枣不同发育期果皮显微结构与裂果的关系

调查结果显示,壶瓶枣裂果主要发生在半红期和全红期,半红期以前裂果率极低。随着果实的发育,枣果皮进入半红期和全红期,表皮和皮下层细胞出现典型的衰老、凋亡特征,表现为细胞变形、皱缩,横向变短、纵向增长,有色物质较多,壁加厚、轮廓不清;表皮细胞出现龟裂,为果皮水分渗透敞开了通道;皮下层厚度的变化直接影响着果皮厚度的变化。受皮下层细胞变形、皱缩的影响,果皮厚度在半红期和全红期变薄,导致果皮破裂应力降低,增加了裂果的风险。果皮结构及形态上的变化可能是造成枣裂果的重要原因。     

Unique envelope of a jellyfish ovum: the armed egg

The eggs of Bougainvillia multitentaculata are spawned with an envelope consisting of a single layer of cnidocvtes. The cnidocytes are surficial On eggs, cleavage stages, and young blastulae. During gastrulation, the cnidocytes are Incorporated intO the ectoderm and become an integral part of the planula.     

Regulation of neurotrophin-3 expression by epithelial-mesenchymal interactions: the role of Wnt factors

Neurotrophins regulate survival, axonal growth, and target innervation of sensory and other neurons. Neurotrophin-3 (NT-3) is expressed specifically in cells adjacent to extending axons of dorsal root ganglia neurons, and its absence results in loss of most of these neurons before their axons reach their targets. However, axons are not required for NT-3 expression in limbs; instead, local signals from ectoderm induce NT-3 expression in adjacent mesenchyme. Wnt factors expressed in limb ectoderm induce NT-3 in the underlying mesenchyme. Thus, epithelial-mesenchymal interactions mediated by Wnt factors control NT-3 expression and may regulate axonal growth and guidance.     

A role for skin gammadelta T cells in wound repair

Gammadelta T cell receptor-bearing dendritic epidermal T cells (DETCs) found in murine skin recognize antigen expressed by damaged or stressed keratinocytes. Activated DETCs produce keratinocyte growth factors (KGFs) and chemokines, raising the possibility that DETCs play a role in tissue repair. We performed wound healing studies and found defects in keratinocyte proliferation and tissue reepithelialization in the absence of wild-type DETCs. In vitro skin organ culture studies demonstrated that adding DETCs or recombinant KGF restored normal wound healing in gammadelta DETC-deficient skin. We propose that DETCs recognize antigen expressed by injured keratinocytes and produce factors that directly affect wound repair.     

Ectodermal Wnt function as a neural crest inducer

Neural crest cells, which generate peripheral nervous system and facial skeleton, arise at the neural plate/ectodermal border via an inductive interaction between these tissues. Wnts and bone morphogenetic proteins (BMPs) play roles in neural crest induction in amphibians and zebrafish. Here, we show that, in avians, Wnt6 is localized in ectoderm and in vivo inhibition of Wnt signaling perturbs neural crest formation. Furthermore, Wnts induce neural crest from naive neural plates in vitro in a defined medium without added factors, whereas BMPs require additives. Our data suggest that Wnt molecules are necessary and sufficient to induce neural crest cells in avian embryos.     

胚胎干细胞体外分化研究进展

胚胎干细胞是来源于胚胎的、内细胞团的、具有多向分化潜能的细胞。随着胚胎干细胞,特别是分化机制研究的不断深入,胚胎干细胞分化为各种类型细胞的研究也取得了较大进展,从而为细胞移植、细胞治疗和组织工程等提供了一个新的途径。主要综述了小鼠和人胚胎干细胞向内、中、外三个胚层细胞类型分化的技术,以期为胚胎干细胞定向诱导分化的研究提供一些参考。     

Recognition of self antigens by skin-derived T cells with invariant gamma delta antigen receptors

Thy-1+ dendritic epidermal T cells (dECs) express invariant gamma delta antigen receptors and are found in intimate contact with keratinocytes in murine epidermis--thus raising the possibility that keratinocytes express a ligand for the antigen receptor of these T cells. Thy-1+ dECs were stimulated to produce lymphokines by interaction with keratinocytes in vitro. This stimulation was mediated through the dEC antigen receptor and did not appear to be restricted by the major histocompatibility complex. Thus, dECs can recognize self antigens and may participate in immune surveillance for cellular damage rather than for foreign antigens.     

Unusual pattern of accumulation of mRNA encoding EGF-related protein in sea urchin embryos

A sea urchin (Strongylocentrotus purpuratus) messenger RNA encoding a protein (SpEGF2) related to epidermal growth factor (EGF) was identified. The full-length complementary DNA sequence predicts a protein with an unusually simple structure, including four tandem EGF-like repeats and a hydrophobic leader, but lacking a potential transmembrane domain. Sequence similarities suggest that the peptides are homologous to two peptides from a different sea urchin species, which cause a classic developmental defect, exogastrulation, when added to the seawater outside of embryos. The SpEGF2 messenger RNA begins to accumulate at blastula stage, and in pluteus larvae it is distributed in discrete regions of ectoderm that are not congruent with known histological borders. One region corresponds to that expressing the homeodomain-containing protein, SpHbox1. The structure of the SpEGF2 protein and the pattern of accumulation of its messenger RNA suggest that it may have important functions as a secreted factor during development of sea urchin embryos.     

Dynamic expression pattern of the myc protooncogene in midgestation mouse embryos

The c-myc protooncogene in mouse embryos was shown by RNA in situ hybridization to be preferentially expressed in tissues of endodermal and mesodermal origin. Most organs developing from the ectoderm, such as skin, brain, and spinal cord, displayed low levels of c-myc RNA. The thymus represented the only hematopoietic organ with high c-myc expression. In organs and structures strongly hybridizing to c-myc probes, for example the fetal part of the placenta, gut, liver, kidney, pancreas, submandibular glands, enamel organs of the molars, and skeletal cartilage, the level of expression depended on the stage of development. Expression was observed to be correlated with proliferation, particularly during expansion and folding of partially differentiated epithelial cells.     

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.     

胚胎干细胞体外定向诱导分化研究进展

胚胎干细胞是由早期内细胞团分离的一种多潜能细胞 ,在体外分化抑制培养时 ,可保持未分化状态而无限增殖。一旦撤除分化抑制因素 ,或添加适当的诱导剂 ,ES细胞可分化为内胚层、中胚层和外胚层的多种类型的特化细胞。文章综述了体外定向诱导 ES细胞分化为造血细胞、心肌细胞、神经细胞、脂肪细胞、胰岛细胞、内皮细胞、上皮细胞、成骨细胞、软骨细胞和黑素细胞等的途径和方法。     

小鼠胚胎中脑神经干细胞分离、培养及分化

目的:探讨小鼠胚胎中脑分离神经干细胞的体外培养方法,以获取高纯度的神经干细胞,为神经干细胞的深入研究提供试验材料。方法:无菌条件下分离孕12~13 d小鼠胚胎中脑曲,制成单细胞悬液,碱性成纤维生长因子(bFGF)和B27存在的培养基中培养扩增,通过免疫细胞化学染色鉴定神经干细胞及子代细胞的分化方向,流式细胞术检测TH阳性神经元比例。结果:培养的部分细胞体外分裂增殖,同时表达神经干细胞特异性抗原nestin,并向神经细胞和胶质细胞分化并经流式细胞仪检测自然分化为多巴胺能神经元的比例为3.25%。结论:小鼠胚脑中脑存在具有多分化潜能的神经干细胞,它们能在体外稳定培养、传代和分化。     

牛表皮祖细胞的体外分离培养

[目的]探索和建立牛表皮祖细胞体外分离与培养体系。[方法]无菌取3个月龄的胎牛皮肤组织,用组织块法培养获得细胞,用L—DMEM培养基（添加5％FBS,0．05mmol／LCaCl2,20ng／mlEGF,20ng／mlbFGF,1％B-27,0．4斗g／mlhydrocortisone）置细胞培养箱内培养。在显微镜下观察细胞的克隆形成能力,免疫细胞化学染色鉴定a6、B1整合素。[结果]获得的细胞有很高的克隆形成能力,a6、p1整合素免疫细胞化学染色阳性。RT—PCR检测结果表明,P,代时Oct4基因有表达,但传代超过P11代时,Oct4基本不表达。[结论]该研究可为进一步采用组织工程技术构建皮肤组织奠定基础。     

表皮干细胞标记物在仿刺参正常和再生体壁中的表达研究

为探究仿刺参表皮再生的机制和再生修复过程中的表皮细胞来源,采用免疫荧光方法,观察β1整合素,α6整合素,角蛋白19 (ck19) 3种表皮干细胞标记物在仿刺参正常及创伤后再生不同时间段的体壁中的表达情况。结果表明ck19在对照组和试验组仿刺参体壁中均呈阳性,并且随着再生的进行,阳性细胞数量和分布区域均有变化。创伤第1天阳性细胞向创伤面上缘迁移,细胞数量同对照组;第3天阳性细胞数量显著下降;第5天阳性细胞数量最多;第7天阳性细胞数量有所下降;11天、13天阳性细胞的数量较第7天稍有增加;第19天阳性细胞数量同对照组,但排列很分散。β1整合素和α6整合素在正常及创伤后再生的体壁中均未见阳性信号出现。结合石蜡切片观察结果进行比较分析认为被ck19标记的细胞是参与仿刺参体壁表皮再生的干细胞和短暂扩增细胞,仿刺参表皮再生的机制属于新建再生。