Molecular basis for the nerve dependence of limb regeneration in an adult vertebrate

The limb blastemal cells of an adult salamander regenerate the structures distal to the level of amputation, and the surface protein Prod 1 is a critical determinant of their proximodistal identity. The anterior gradient protein family member nAG is a secreted ligand for Prod 1 and a growth factor for cultured newt blastemal cells. nAG is sequentially expressed after amputation in the regenerating nerve and the wound epidermis-the key tissues of the stem cell niche-and its expression in both locations is abrogated by denervation. The local expression of nAG after electroporation is sufficient to rescue a denervated blastema and regenerate the distal structures. Our analysis brings together the positional identity of the blastema and the classical nerve dependence of limb regeneration.     

Appendage regeneration in adult vertebrates and implications for regenerative medicine

The regeneration of complex structures in adult salamanders depends on mechanisms that offer pointers for regenerative medicine. These include the plasticity of differentiated cells and the retention in regenerative cells of local cues such as positional identity. Limb regeneration proceeds by the local formation of a blastema, a growth zone of mesenchymal stem cells on the stump. The blastema can regenerate autonomously as a self-organizing system over variable linear dimensions. Here we consider the prospects for limb regeneration in mammals from this viewpoint.     

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.     

Regeneration of the amputated amphibian limb: retardation by hemicholinium-3

Doses of hemicholinium-3 which partially paralyze the larval salamander profoundly retarded regeneration of the amputated hind limb. The drug also reduced the vascularity and mitotic index of the regenerating tissue. After withdrawal of the drug the rate of regeneration returned to normal. Atropine, in a daily dose of 40 milligrams per kilogram of body weight, did not retard growth. These findings suggest that in the salamander acetylcholine may mediate neurotrophic activity.     

Ectoderm to mesoderm lineage switching during axolotl tail regeneration

Foreign environments may induce adult stem cells to switch lineages and populate multiple tissue types, but whether this mechanism is used for tissue repair remains uncertain. Urodele amphibians can regenerate fully functional, multitissue structures including the limb and tail. To determine whether lineage switching is an integral feature of this regeneration, we followed individual spinal cord cells live during tail regeneration in the axolotl. Spinal cord cells frequently migrate into surrounding tissue to form regenerating muscle and cartilage. Thus, in axolotls, cells switch lineage during a real example of regeneration.     

Expression of the multidrug-resistant gene in hepatocarcinogenesis and regenerating rat liver

Preneoplastic and neoplastic liver nodules and hepatocytes isolated from regenerating rat liver have been shown to be resistant to a broad range of carcinogenic agents. This phenomenon was studied by measuring the expression of the multidrug-resistant (mdr) gene in normal liver cells and in preneoplastic and neoplastic nodules and regenerating liver. Levels of messenger RNA for the mdr gene, which encodes P-glycoprotein, were elevated in both preneoplastic and neoplastic lesions. Expression of the mdr gene also reached high levels in regenerating rat liver 24 to 72 hours after partial hepatectomy. These results show that the expression of the mdr gene can be regulated in liver and is likely to be responsible for part of the multidrug-resistance phenotype of carcinogen-initiated hepatocytes and regenerating liver cells.     

不同采集方式对马尾松林天然更新的影响

利用面积为 1 4.33hm2 的固定试验区 ,定位研究不同采集作业方式对马尾松次生阔叶混交林天然更新效果的影响 .结果表明 :主伐强度不同 ,对马尾松次生林更新密度、更新频度和1年生幼苗各器官生长量都有显著影响 ;集材有利于种子的着床发芽 ,对更新密度有显著影响 ,但对更新频度和幼苗生长无明显影响     

皇家嘎拉苹果试管苗叶片再生不定芽的试验

以皇家嘎拉苹果试管苗叶片为试材,采用正交试验设计,研究了氮形态比例(NH4+∶NO3-)、6-BA浓度、NAA浓度对叶片再生不定芽的影响.结果表明:3因素对叶片再生不定芽影响的顺序依次为:氮形态比例(NH4+∶NO3-)>NAA浓度>BA浓度,其中氮形态比例对叶片再生不定芽的影响达到显著水平.3因素水平的最佳不定芽再生组合为:氮形态比例(NH4+∶NO3-)=2∶0,6-BA 2.0 mg/L,NAA 0.1 mg/L的MS培养基.在氮形态比例(NH4+∶NO3+)=2∶0的基础上,进行6-BA、NAA小梯度筛选,结果显示,皇家嘎拉苹果试管苗叶片再生不定芽较高再生频率的培养条件为:6-BA 2.0 mg/L,NAA 0.15 mg/L的改良MS培养基.     

Electrophysiologic responses in hamster superior colliculus evoked by regenerating retinal axons

Autologous peripheral nerve grafts were used to permit and direct the regrowth of retinal ganglion cell axons from the eye to the ipsilateral superior colliculus of adult hamsters in which the optic nerves had been transected within the orbit. Extracellular recordings in the superior colliculus 15 to 18 weeks after graft insertion revealed excitatory and inhibitory postsynaptic responses to visual stimulation. The finding of light-induced responses in neurons in the superficial layers of the superior colliculus close to the graft indicates that axons regenerating from axotomized retinal ganglion cells can establish electrophysiologically functional synapses with neurons in the superior colliculus of these adult mammals.     

Development of a receptor on a foreign nerve fiber in a Pacinian corpuscle

When the sensory fiber of a Pacinian corpuscle (in cat mesentery) is transected (at the inferior mesenteric nerve) transduction fails within 30 hours: the nerve ending produces no generator potentials in response to mechanical stimulation. Electrically elicited nerve impulse conduction continues for at least another 18 hours. A transducer mechanism develops on a regenerating nerve fiber when this fiber enters the denervated corpuscle. Such transducer development takes place on myelinated fibers from the inferior mesenteric nerve, which normally supplies corpuscles, as well as on myelinated hypogastric nerve fibers, which normally do not go to corpuscles, including fibers larger than the original corpuscle afferents.     

Biosynthess of histones and acidic nuclear proteins under different conditions of growth

The incorporation of uniformly labeled L-lysine-C(14) into the normal and regenerating rat liver, into Novikoff hepatoma histones, and into acidic nuclear proteins was studied. In rat liver, different histone fractions incorporate labeled lysine to a different extent. Such differences become less obvious in regenerating liver, and they are even less so in Novikoff hepatoma. In the hepatoma cells the ratio of the biosynthesized acidic nuclear proteins to histones was altered.     

甘谷线辣椒继代培养快速繁殖培养基的研究

本试验是在1988～1990年期间对甘谷线辣椒继代苗筛选出较适宜的培养基的基础上,为了使植株生长健壮,提高繁殖系数,我们以B_5培养基为基础,加入不同药剂处理,筛选出植株生长健壮,根系发达,年繁殖系数可达478万株的B_3培养基。该结果对用辣椒组织培养的方法以及快速繁殖辣椒,保存优良株系等方面有较大意义。     

金针菇的原生质体单核化

采用显微镜单孢分离技术从金针菇菌株 FL19(黄色品种 )和 880 1(白色品种 )分离刚萌发的原生质体再生菌株 ,分别获得 89和 83株单个原生质体再生菌株 ,并对它们的不亲和性因子基因型进行测定 .结果表明 ,两个亲本的不亲和性因子 A和 B都存在 3个复等位基因 .原生质体单核化技术可为白色金针菇的品种改良提供一个新途径     

Scaling body support in mammals: limb posture and muscle mechanics

The scaling of bone and muscle geometry in mammals suggests that peak stresses (ratio of force to cross-sectional area) acting in these two support elements increase with increasing body size. Observations of stresses acting in the limb bones of different sized mammals during strenuous activity, however, indicate that peak bone stress is independent of size (maintaining a safety factor of between 2 and 4). It appears that similar peak bone stresses and muscle stresses in large and small mammals are achieved primarily by a size-dependent change in locomotor limb posture: small animals run with crouched postures, whereas larger species run more upright. By adopting an upright posture, large animals align their limbs more closely with the ground reaction force, substantially reducing the forces that their muscles must exert (proportional to body mass) and hence, the forces that their bones must resist, to counteract joint moments. This change in limb posture to maintain locomotor stresses within safe limits, however, likely limits the maneuverability and accelerative capability of large animals.     

玉米自交系幼胚高效再生系统的建立

以22份玉米自交系为试验材料,以幼胚为外植体,研究基因型、诱导（分化）培养基、继代次数、Ag-NO3浓度对玉米幼胚胚性愈伤组织的诱导、保持和植株分化的影响。结果表明,玉米幼胚培养能力受基因型、培养基及二者互作效应的影响,基因型是主要的影响因子。3 mg/L的2,4-D对胚性愈伤组织诱导和保持起关键作用;0.5 mg/L 6-BA抑制胚性愈伤组织的发生;8-12 mg/L AgNO3明显改善部分基因型愈伤组织质量,提高胚性愈伤组织诱导率。分化培养基中添加1 mg/L的KT和0.5 mg/L的IBA促进绿苗的分化和根系的生长。胚性愈伤组织继代3-5次后调整到最佳状态。确定了玉米幼胚培养胚性愈伤组织诱导的最佳培养基为N6＋3 mg/L 2,4-D＋8-12 mg/L AgNO3＋0.2 mg/L IAA,最佳分化培养基为N6＋1 mg/L KT＋0.5 mg/L IBA。     

Astrocytes block axonal regeneration in mammals by activating the physiological stop pathway

Regenerating sensory axons in the dorsal roots of adult mammals are stopped at the junction between the root and spinal cord by reactive astrocytes. Do these cells stop axonal elongation by activating the physiological mechanisms that normally operate to stop axons during development, or do they physically obstruct the elongating axons? In order to distinguish these possibilities, the cytology of the axon tips of regenerating axons that were stopped by astrocytes was compared with the axon tips that were physically obstructed at a cul-de-sac produced by ligating a peripheral nerve. The terminals of the physically obstructed axon tips were distended with neurofilaments and other axonally transported structures that had accumulated when the axons stopped elongating. By contrast, neurofilaments did not accumulate in the tips of regenerating axons that were stopped by spinal cord astrocytes at the dorsal root transitional zone. These axo-glial terminals resembled the terminals that axons make on target neurons during normal development. On the basis of these observations, astrocytes appear to stop axons from regenerating in the mammalian spinal cord by activating the physiological stop pathway that is built into the axon and that normally operates when axons form stable terminals on target cells.     

Radar scattering from venus at large angles of incidence and the question of polar ice caps

Spectrum analysis of radar waves backscattered from an anulus near the limb of Venus shows that a uniform scattering model applies over regions extending from the equator to within approximately 15 degrees of the poles. These observations indicate that large polar ice caps extending to latitudes as low as 60 degrees are very unlikely.     

Distal regeneration and symmetry

A revision of the "polar coordinate model" shows how pattern formation in diverse regenerating systems can be understood in terms of strictly local cell interactions.     

Diurnal rhythm: effects on hepatic regeneration and hepatic regenerative stimulator substance

The effect of a controlled lighting schedule on the activity of a weanling rat liver extract that stimulates DNA synthesis in regenerating adult rat liver, and on the response of the test animals to the extract, has been investigated. Both activity of the extract and endogenous DNA synthesis in the weanling animals follow the same distinct diurnal rhythm. Reversal of the lighting schedule reverses the rhythm of endogenous DNA synthesis but activity of the extract no longer correlates with the peak of DNA synthesis. Diurnal rhythm also has a striking effect on DNA synthesis in the regenerating test animal, but the extract increases DNA synthesis to the same relative degree, regardless of the time of day the hepatectomy is performed.     

蜗牛酶高效制备白色念珠菌原生质体的研究

为了寻求以蜗牛酶经济高效的白色念珠菌原生质体的制备方法,以白色念珠菌为材料,研究了菌龄、预处理剂、酶浓度、作用时间、高渗稳定剂等因素对原生质体制备率和再生率的影响。结果表明,以蜗牛酶制备白色念珠菌原生质体的最佳菌龄是培养10～14 h的菌体,最佳预处理剂配方为50 mmol/L Tris(pH8.0)、50 mmol/L EDTA和5%巯基乙醇,1%蜗牛酶在37℃酶解1 h原生质体制备率可达90%以上,此原生质体采用夹层平板培养法在0.7 mol/L NaCl高渗培养基中培养,再生率最高可达95%。本研究表明单独用蜗牛酶高效制备高质量的白色念珠菌原生质是可行的。