Beta-catenin defines head versus tail identity during planarian regeneration and homeostasis

After amputation, freshwater planarians properly regenerate a head or tail from the resulting anterior or posterior wound. The mechanisms that differentiate anterior from posterior and direct the replacement of the appropriate missing body parts are unknown. We found that in the planarian Schmidtea mediterranea, RNA interference (RNAi) of beta-catenin or dishevelled causes the inappropriate regeneration of a head instead of a tail at posterior amputations. Conversely, RNAi of the beta-catenin antagonist adenomatous polyposis coli results in the regeneration of a tail at anterior wounds. In addition, the silencing of beta-catenin is sufficient to transform the tail of uncut adult animals into a head. We suggest that beta-catenin functions as a molecular switch to specify and maintain anteroposterior identity during regeneration and homeostasis in planarians.     

Smed-betacatenin-1 is required for anteroposterior blastema polarity in planarian regeneration

Planarian flatworms can regenerate heads at anterior-facing wounds and tails at posterior-facing wounds throughout the body. How this regeneration polarity is specified has been a classic problem for more than a century. We identified a planarian gene, Smed-betacatenin-1, that controls regeneration polarity. Posterior-facing blastemas regenerate a head instead of a tail in Smed-betacatenin-1(RNAi) animals. Smed-betacatenin-1 is required after wounding and at any posterior-facing wound for polarity. Additionally, intact Smed-betacatenin-1(RNAi) animals display anteriorization during tissue turnover. Five Wnt genes and a secreted Frizzled-related Wnt antagonist-like gene are expressed in domains along the anteroposterior axis that reset to new positions during regeneration, which suggests that Wnts control polarity through Smed-betacatenin-1. Our data suggest that beta-catenin specifies the posterior character of the anteroposterior axis throughout the Bilateria and specifies regeneration polarity in planarians.     

Polarized notum activation at wounds inhibits Wnt function to promote planarian head regeneration

Regeneration requires initiation of programs tailored to the identity of missing parts. Head-versus-tail regeneration in planarians presents a paradigm for study of this phenomenon. After injury, Wnt signaling promotes tail regeneration. We report that wounding elicits expression of the Wnt inhibitor notum preferentially at anterior-facing wounds. This expression asymmetry occurs at essentially any wound, even if the anterior pole is intact. Inhibition of notum with RNA interference (RNAi) causes regeneration of an anterior-facing tail instead of a head, and double-RNAi experiments indicate that notum inhibits Wnt signaling to promote head regeneration. notum expression is itself controlled by Wnt signaling, suggesting that regulation of feedback inhibition controls the binary head-tail regeneration outcome. We conclude that local detection of wound orientation with respect to tissue axes results in distinct signaling environments that initiate appropriate regeneration responses.     

A pericyte origin of spinal cord scar tissue

There is limited regeneration of lost tissue after central nervous system injury, and the lesion is sealed with a scar. The role of the scar, which often is referred to as the glial scar because of its abundance of astrocytes, is complex and has been discussed for more than a century. Here we show that a specific pericyte subtype gives rise to scar-forming stromal cells, which outnumber astrocytes, in the injured spinal cord. Blocking the generation of progeny by this pericyte subtype results in failure to seal the injured tissue. The formation of connective tissue is common to many injuries and pathologies, and here we demonstrate a cellular origin of fibrosis.     

Geckos: adaptive significance and energetics of tail autotomy

Coleonyx variegatus is adapted to readily sacrifice its tail to predators. This adaptation is associated with characteristic tail behavior and rapid tail regeneration. There is no facultative metabolic increase associated with tail regeneration, and energy normally allocated to body growth and maintenance is diverted to tail regeneration. This supports the contention that tail behavior, autotomy, and rapid regeneration evolved as mechanisms promoting survival in terms of predator escape.     

Human monocytic cell lines derived from cord leukocytes by co-cultivation with irradiated CM-S cells

The CM-S cell line was established from the bone marrow of a child with congenital hypoplastic anemia and resembles its monocyte-macrophage lineage. Lethally x-irradiated CM-S cells from various passages and clones, representing different stages in the progression of the transformed growth phenotype, were tested for their ability to affect the survival and proliferation of normal human cord or adult blood leukocytes in co-culture. One clone, CM-SM, which is tumorigenic in athymic mice, consistently immortalized umbilical cord mononuclear cells but did not immortalize adult peripheral blood leukocytes. Six autonomous monocyte-like diploid cell lines were obtained and all were found to be of cord origin. Three lines were tumorigenic in athymic mice. Attempts to immortalize human leukocytes with cell-free supernatants from CM-S cells were unsuccessful.     

Increased Wnt signaling during aging alters muscle stem cell fate and increases fibrosis

The regenerative potential of skeletal muscle declines with age, and this impairment is associated with an increase in tissue fibrosis. We show that muscle stem cells (satellite cells) from aged mice tend to convert from a myogenic to a fibrogenic lineage as they begin to proliferate and that this conversion is mediated by factors in the systemic environment of the old animals. We also show that this lineage conversion is associated with an activation of the canonical Wnt signaling pathway in aged myogenic progenitors and can be suppressed by Wnt inhibitors. Furthermore, components of serum from aged mice that bind to the Frizzled family of proteins, which are Wnt receptors, may account for the elevated Wnt signaling in aged cells. These results indicate that the Wnt signaling pathway may play a critical role in tissue-specific stem cell aging and an increase in tissue fibrosis with age.     

杉木愈伤组织及再生芽分化的细胞学观察

研究杉木愈伤组织形成及再生芽分化过程中的细胞组织发育规律,为建立杉木遗传转化体系提供科学依据。以杉木茎段为外植体,通过对组织培养条件下产生的愈伤组织进行体视显微镜和石蜡切片观察,分析愈伤组织的结构、形成及再生芽分化过程中的细胞组织变化规律。结果表明:愈伤组织先是由杉木茎段切口处表皮细胞分裂,再由维管束薄壁细胞通过脱分化逐渐形成的;愈伤组织在增殖期间分生细胞会形成不同维管组织;愈伤组织的再生芽分化是由愈伤组织的表皮分生细胞团先分化形成芽原基,再形成肉眼可见的再生芽;不定芽可从茎段直接分化形成,亦可通过愈伤组织再分化形成,两种不定芽发生方式均为外起源。     

梅花鹿鹿茸细胞端粒酶活性及其mRNA表达的检测

[目的]研究鹿茸生长期端粒酶的表达,为揭示鹿茸生长发育的调控机制提供了新思路。[方法]在鹿茸快速生长阶段,采用改进的TRAP（端粒重复序列扩增技术）法检测鹿茸顶端增殖区的间充质层、前软骨层和软骨层细胞及下端成熟区的端粒酶活性。同时,采用RT-PCR的方法检测各组织细胞中端粒酶催化亚基（TERT）mRNA的表达水平。[结果]在顶端增生区各组织细胞中均检测到了不同程度的端粒酶活性,间质细胞、前软骨细胞和软骨细胞中的相对端粒酶活力分别为91.2、46.4和13.7,而在成熟区组织中则检测不到端粒酶活性。RT-PCR法检测的各组织细胞中TERTmRNA的表达水平与端粒酶活性检测结果一致。[结论]在鹿茸快速生长阶段,其增殖区表达端粒酶,并且端粒酶活性随组织层细胞的分化程度的增高而逐渐降低,说明端粒酶可能在鹿茸的生长过程中起重要的调控作用。     

大鲵脂肪组织分布及其理化特性

从大鲵的尾部开始,每隔1 cm切取大鲵肉块,观察其脂肪组织分布;通过石蜡切片、HE染色后观察脂肪细胞;通过流变仪测定大鲵脂肪粘度;通过气相色谱/质谱联用技术分析大鲵脂肪的脂肪酸组成。结果表明,大鲵脂肪主要集中于尾部2/3处至尾尖,尾部2/3处至尾鳍部脂肪含量显著减少,尾鳍部只存在极少量的皮下脂肪;脂肪细胞有较强的流动性,易变形、易碎;脂肪具牛顿流体特性,粘度为0.0289Paos;大鲵脂肪主要含13种脂肪酸(C18:124.2%,C16:015.4%,C16:113.7%,C18:28.2%,C20:56.7%,C18:34.5%,C22:64.3%,C14:13.0%,C18:02.8%,C22:52.6%,C20:42.2%,C17:02.0%,C17:11.9%)。     

Bone marrow stromal cells generate muscle cells and repair muscle degeneration

Bone marrow stromal cells (MSCs) have great potential as therapeutic agents. We report a method for inducing skeletal muscle lineage cells from human and rat general adherent MSCs with an efficiency of 89%. Induced cells differentiated into muscle fibers upon transplantation into degenerated muscles of rats and mdx-nude mice. The induced population contained Pax7-positive cells that contributed to subsequent regeneration of muscle upon repetitive damage without additional transplantation of cells. These MSCs represent a more ready supply of myogenic cells than do the rare myogenic stem cells normally found in muscle and bone marrow.     

东亚三角涡虫DjStag基因干扰载体的构建及干扰效果鉴定

 构建DjStag基因的RNA干扰表达载体,诱导表达产生dsRNA后喂食涡虫,观察DjStag表达变化及对涡虫再生的影响。本文以含有东亚三角涡虫DjStag基因的pcDNA3 DjStag重组质粒为模板,经PCR 扩增目的片段,将其克隆到干扰载体L4440 上,构建重组质粒L4440 DjStag后转化入大肠杆菌HT115感受态细胞中, IPTG 诱导表达dsRNA后喂食涡虫。显微观察涡虫再生过程中的表型变化,Real time PCR检测干扰后涡虫DjStag基因表达的变化。结果表明,成功构建了DjStag基因的RNA干扰表达载体;DjStag基因 RNA干扰后,涡虫不能正常再生,再生片段显示出明显的再生缺陷;涡虫体内DjStag基因的表达受到抑制,DjStag mRNA的表达水平显著下降。     

海参再生研究进展

综述了国内外关于海参再生的研究进展,介绍了海参各部位再生研究进展,以期为高等动物的细胞分化与增殖、组织修复的完整机制提供理论基础。     

新疆大叶紫花苜蓿两种再生体系的比较

分别以新疆大叶紫花苜蓿幼苗的叶片和切去胚根的子叶为外植体,比较了传统胚胎发生途径和器官发生途径的两种不同的再生过程对苜蓿再生周期和再生频率的影响,初步得出器官发生途径是一种可行的快速高效的再生途径。结果表明,从种子处理到再生幼苗的生成,利用成熟种子的胚诱导分化成苗可以大大缩短再生周期,提高再生频率,是明显优于胚胎发生途径的另一种再生方式。     

Neuroscience. Stem cells hear call of injured tissue

In animal models, injected stem cells travel to tissue injured by stroke, Alzheimer's-like plaques, contusions, or spinal cord bruises, sometimes traversing long distances. Several teams reported these surprising results this month at the Society for Neuroscience annual meeting. No one knows exactly how stem cells detect these different kinds of damage, but researchers hope that the cells' migratory powers can be harnessed to either replace dead tissue or deliver therapeutics right where they're needed.     

Synaptic potentials recorded in cell cultures of nerve and muscle

Initially dissociated spinal cord and muscle cells derived from chick embryos differentiate sufficiently in tissue culture to form functional synaptic contacts. Spontaneous and evoked potentials recorded with intracellular microelectrodes resemble synaptic responses of adult spinal cord and neuromuscular junctions.     

fgf20 is essential for initiating zebrafish fin regeneration

Epimorphic regeneration requires the presence or creation of pluripotent cells capable of reproducing lost organs. Zebrafish fin regeneration is mediated by the creation of blastema cells. Here, we characterize the devoid of blastema (dob) mutant that fails fin regeneration during initial steps, forms abnormal regeneration epithelium, and does not form blastema. This mutation has no impact on embryonic survival. Dob results from an fgf20a null mutation, Y148S. Fgf20a is expressed during initiation of fin regeneration at the epithelial-mesenchymal boundary and later overlaps with the blastema marker msxb. Thus, fgf20a has a regeneration-specific requirement, initiating fin regeneration, and controlling blastema formation.