Ersatzgewebe aus Bioreaktoren

Induced Stem Cells and Tissue Engineering Not only ethical reservations and restrictive laws direct medically oriented stem cell research towards adult stem cells, facilitated by new methods to reprogram differentiated cells back to proliferating progenitors. This allows new therapies with autologous, immunologically tolerant cells and tissues. In bioreactors autologous tissues are grown to replace, for instance, burned skin, cartilaginous elements, and heart valves. Even almost complete eyes, however in an embryonic state, can develop from stem cells in culture by self organization. Finally the German laws related to stem cell research are reviewed.     

中国绿水螅分子系统发生地位的初步探讨

目的:初步探讨中国绿水螅(Hydra sinensis)分子系统发生地位以及水螅属内部各类群系统发生关系。方法:采用酚-氯仿法提取中国绿水螅总DNA,扩增线粒体COI和16S r RNA基因片段并进行DNA序列测定,再利用Clustal及MEGA等生物信息学分析软件进行系统发生分析。结果:在本研究重建的所有系统发生树中,中国绿水螅始终与绿水螅Hydra viridissima的不同种群一起构成绿水螅单系群。同时,棕色水螅群的单系性被基于COI基因的NJ树以及基于16S r RNA基因的NJ树和ML树支持,唯独基于COI基因的ML树不支持棕色水螅群的单系发生。在基于COI基因的ML树中纤弱水螅族在系统树的基部独立为一支系,而绿水螅群和其他棕色水螅群水螅一起组成另一支系,提示纤弱水螅族水螅的系统发生地位值得进一步探讨。值得注意的是,根据本文的结果,棕色水螅群内3族的划分仍然有一定疑问。基于COI基因的NJ树和ML树支持普通水螅族、寡水螅族和纤弱水螅族各自族内的单系发生,但16S r RNA基因的NJ树和ML树中仅普通水螅族水螅聚为单系群,而寡水螅族和纤弱水螅族水螅各自并非单系发生。结论:把水螅属划分为绿水螅群及棕色水螅群有一定的合理性,但棕色水螅群内寡水螅族、普通水螅族和纤弱水螅族3族的划分还有待商榷。     

普通水螅(无鞘螅目,水螅科)中国一新纪录种

对采自中国广东省珠江流域(114°E,23°N)的一种淡水水螅进行连续两年的培养与观察,并扩增了其线粒体细胞色素氧化酶亚基Ⅰ(COⅠ)的基因序列.通过形态学分析及CO Ⅰ基因序列的鉴定确定其为普通水螅Hydra vulgaris Pallas,1766,为中国一新纪录种.     

强壮水螅的特征及其与寡水螅的种间差别问题

一种广泛分布于黑龙江省的大型具柄水螅被暂定为强壮水螅Hydra robusta(IT(?) 1947)。这一中国品系与IT(?)(1947)在日本报告的新种主要特征相同,包括具有精巢乳头。只是精巢乳头不稳定。在实验室条件下第一次有性生殖时每个雄体都发生精巢乳头,但第二次有性生殖时,同一群的后代可全部失去精巢乳头。这是介于强壮水螅与寡水螅Hydra oligactis Pallas(1766)之间的中间性状。从而导致作者做出结论,认为过去其他学者所主张的,以精巢乳头的有无做为鉴别特征来区分强壮水螅和寡水螅是不可靠的。因此,本文又检验了此种水螅的体细胞染色体,证明2n=30,其中第二对染色体上有明显近中位置的次缢痕,最小染色体的长度为最大染色体长度的二分之一以上。这些可做为此种水蝗的鉴别特征。对Niiyama(1944)和Datta(1970)在寡水螅上所做的染色体研究也做了比较及讨论。     

Bud formation inHydra: Inhibition by an endogenous morphogen

Summary From crude extracts ofHydra tissue a substance has been purified which prevents or retards the asexual reproduction by budding. The molecular weight is in the range of 300 to 1000 daltons. Inhibition of bud formation can be observed with concentrations equivalent to the extract from one hydra per 4 ml, that is, to a more than 10,000-fold dilution of the initial crude extract of a hydra. The purified inhibitor is active at a concentration of less than 10^–8 M.Most of the inhibitor present inHydra is bound to cells. Within the cells the substance is mainly bound to particulate structures which sediment at 10,000 g. Its concentration is highest in the hypostomal region and decreases in the direction of the tentacles and peduncle. A second, lower, peak has been found in the basal disc. Treatment of the animals with a toxic agent (nitrogen mustard) which depletes the animal of interstitial cells, nematocytes and nematoblasts excludes the possibility that the inhibitor is present to any great extent in these cells. In conjunction with cell separation experiments by centrifugation of fixed cells in suspension, these results indicate that nerve cells are the most likely sites of storage of the inhibiting substance, although epithelial cells are not excluded as sources for the inhibitor.     

Hydra pattern is controlled by two distinct but interacting morphogen sets

Summary Temporal course of regeneration of the hypostome and basal disc along the body length of the hydra is studied both in the presence and absence of the other determined centre. The regeneration times vary nonlinearly with distance from the original position indicating that the underlying processes are of non-linear nature. The presence of hypostome influences the regeneration of basal disc in an inhibitory manner throughout the body length, whereas, basal disc influences the regeneration of hypostome only in the lower portion of the body in a positive manner. A scheme in terms of the activators and inhibitors specific to hypostome and basal disc, is given. The implication of these results is that the two inhibitors are functionally distinct.     

Biosynthetic events of hydrid regeneration

Summary The results of a combined morphological and biochemical study of the role of DNA synthesis during distal regeneration inHydra oligactis revealed that a burst of³H-thymidine incorporation into DNA preceded the elaboration of each of the initial three tentacles. In addition, the relative level of each burst of precursor incorporation relfected the number of tentacles formed at that time. Cytological localization of concentrated amounts of labeled material in nuclei of the hypostome and tentacle regions provided corroborative evidence for the biochemical findings.Evidence that the increased DNA specific activity levels described above are associated with tentacle initiation derived from studies in which regenerating hydra were cultured in hydroxyurea and studies in which hydra regenerated proximally rather than distally. Hydra regenerating in 8 mg/ml (0.105 M) hydroxyurea developed morphologically recognizable hypostomes but no tentacles, and incorporated³H-thymidine into DNA at a level distinctly below that exhibited by uncut, untreated animals. Similarly, hydra regenerated a normal, functional basal disc in the absence of any increased DNA specific activity. Therefore, it is suggested that tentacle initiation inH. oligactis requires concomitant DNA synthesis and, as such, represents an epimorphic phenomenon.     

Head activator does not qualitatively alter head morphology in regenerates ofHydra oligactis

Summary The characterization of head activator (HA) as a morphogen capable of increasing the number of tentacles regenerated by hydra was re-examined. Gastric tissue was excised from HA-treated whole animals and allowed to regenerate. At the cellular level the differentiation of head-specific ectodermal epithelial cells was monitored by quantifying monoclonal antibody, CP8, labeling. This labeling has been correlated with a rise in head activation potential and the determination of tissue to form head structures (Javois et al. 1986). At the morphological level tentacle number was monitored. HA-treated regenerates began the head patterning processes and evaginated tentacles sooner than controls but did not produce extra tentacles. The kinetics of CP8 labeling did not reveal major differences between treated and control regenerates after the initiation of head-specific epithelial cell differentiation. HA appeared to act more like a growth factor stimulating the differentiation of head-specific cell types rather than a morphogen which altered head morphology. An additional aspect of the study examined axial-specific effects of HA on the initiation and extent of head-specific epithelial cell differentiation. The cellular response of ectodermal epithelial cells to HA was dependent on their original axial location. More CP8⁺ tissue differentiated in regenerates of apical as opposed to mid-gastric origin.     

Regulation of Numbers of Algae in the Hydra-Chlorella Symbiosis

Algae injected into green hydra are taken up rapidly and in relatively large numbers, resulting in an increased symbiont population in digestive cells. The increase is temporary and the normal stock population size is restored within 24 hours after injection. Restoration of the normal population size is taken as evidence for regulation, and the technique offers a means for eliciting and studying at least one type of regulatory mechanism. Similarly, a method is described for rapid assay and visualization of digestive cell mitosis. This method may facilitate the investigation of other potential regulatory mechanisms which may involve interaction between host and algal cell division. Finally, symbiont overgrowth of host cells resulting from nutrient enrichment is described. The observations lend support to the hypothesis that nutrient limitation may regulate population size of algal symbionts.     

Head regeneration inHydra is initiated release of head activator and inhibitor

Summary Hydra regenerating heads release at least two substances into the surrounding medium: one stimulates and one inhibits head formation. The inhibitor is released mainly during the first hour after cutting, the activator is released more slowly with a maximum in the second hour and with substantial release still during the following six hours. The release of both substances seems to be specific for head regeneration: it is not found in animals regenerating feet. The sequential release of these substances leads to the early changes observed at the cellular level during head regeneration inhydra: the inhibitor produces a decrease, the activator an increase in the mitotic activity of interstitial and epithelial cells, if assayed on intact animals. Head regeneration is blocked, if the release of the head activator is prevented. It is therefore suggested that these substances are necessary to initiate head regeneration inhydra.     

Therapie mit Stammzellen

Therapeutic use of stem cells Here the hematopoetic system of blood‐ and immune cell renewal is reviewed. Curing of chronic leucemias and malignant lymphomas is the most successful stem cell based therapy up to date. However, mismatches of histocompatibility‐complexes (HLA‐types) between receiver and donor set narrow limits to such therapies. Whether other diseases such as Parkinson could be cured by infusion of stem cells is still in question.     

A four-variable model for the pattern-forming mechanism in Hydra

A generalized Gierer-Meinhardt model has been used to account for the transplantation experiments in Hydra. In this model, a cross inhibition between the two organizing centres (namely, head and foot) are assumed to be the only mode of interaction in setting up a stable morphogen distribution for the pattern formation in Hydra.     

Effects of Altered Light and Feeding Regimes on the Zooplankton Feeding Capability of Hydra viridis

The effects of light regime, feeding regime and tentacle number on the zooplankton feeding capability of Hydra viridis were tested in the laboratory. Feeding was measured by exposing Hydra to a known volume of Artemia salina nauplii and recording the number captured and ingested. In all cases there was a correlation between the number of Artemia captured and the number ingested. H. viridis with 7 tentacles captured and ingested more Artemia than Hydra with 6 tentacles. However, changes in light and/or feeding regimes did not alter the number of tentacles/Hydra. Varying light and feeding regimes altered the number of Zoochlorellae/cell and Hydra growth rate. There was no effect on the number of Artemia captured or ingested and no effect on the percent ingestion of captured Artemia. These data suggest that, under these conditions, zooplankton feeding by H. viridis is independent of nutritional history.     

Characterisation of two types of head activator receptor on hydra cells

A head activator (HA) analogue is described which even at high concentrations does not lose its biological activity. By cross-linking two HA molecules over a C8 spacer, the conformation was sufficiently altered, such that self-inactivation of HA by dimerisation was prevented. In addition, the introduction of a tyrosine instead of phenylalanine in one of the two HA molecules allowed radioactive labelling with iodine. This HA bipeptide was used to investigate the effect of HA at different concentrations and as ligand for HA receptor characterisation. We found that low concentrations (0.1-10 pM) sufficed to stimulate interstitial cell mitosis, and that higher concentrations (10-1000 pM) were required for the determination of interstitial cells to nerve cells. Binding of the radioactive HA ligand to living hydra and to purified membrane fractions was saturable and specific. Binding was compatible with HA analogues with a stable monomeric conformation, but less well with dimerising HA and HA analogues. Scatchard and kinetic analyses revealed the presence of at least two types of binding site in the membrane fraction, one with a 'lower' affinity (Kd = 10(-9) M) and one with a 100-fold higher affinity (Kd = 10(-11) M). Autoradiography showed that interstitial cells were differentially labelled, suggesting that the number or types of HA receptors may vary depending on cell cycle status. A mutant of hydra with a multiheaded morphology contained 6-20-times more HA receptors per mg protein than other hydra species or mutants.     

Separation and specificity of action of four morphogens from hydra

Summary A procedure is presented by which four previously described morphogenetic substances can be purified from hydra: an activator and an inhibitor of head formation and an activator and an inhibitor of foot formation. We show that all four substances act specifically. At low concentrations, the head factors only influence head and not foot formation, and the foot factors only influence foot and not head formation.