Regulation factor for planarian regeneration

Planarian head extract was fractionated and the fractions were assayed for their effect on cultured cells and planarian regeneration. One fraction (molecular weight larger than 10 000; unadsorbable by DEAE-Sephadex, CM-Sephadex and Con A-Sepharose; and precipitable by ammonium sulfate) inhibited the growth of both Neuro 2a and PC-12 cell lines as well as planarian head- regeneration. This effect was specific for head-regeneration (regeneration of tails was not influenced), trypsin sensitive, reversible and stable after heat-treatment at 80° C for 30 min.     

miRNA与涡虫再生

miRNA是一类具有调节功能的非编码小分子RNA,参与调节多种细胞功能。涡虫具有强大的再生能力,逐渐成为干细胞功能和再生研究的良好的动物模型。本文对miRNA在动物再生中的功能,尤其是miRNA与涡虫再生的关系进行综述。     

Differentiation of epidermal cells in the regenerating planarian Dugesia japonica

Distribution of the cytoplasmic components in planarian epidermal cells is highly polarized, just as in vertebrate epithelia. Differentiating epidermal cells of the planarian Dugesia japonica Ichikawa et Kawakatsu were found to have relatively conspicuous accumulations of microtubules in their apical cytoplasm. When colchicine, a microtubule-disrupting drug, was applied to regenerating worms, it reversibly disorganized the polarity of differentiating epidermal cells. Cytochalasin B, which depolymerizes actin filaments, had no significant effect on the polarization, however. Tubulin could be localized by immunocytochemistry in the cytoplasm of differentiating epidermal cells; this reaction was inhibited by treatment with colchicine for 20 h. These observations indicate that microtubules play a role in establishing polarity during cell differentiation.     

涡虫wnt基因的研究进展

涡虫具有强大的再生能力,对其再生机制等方面的研究一直是发育生物学研究的热点问题。Wnt信号途径是动物发育中关键的信号途径之一,对生物的生长发育有着至关重要的作用,近年来国内外对涡虫的wnt基因进行了不断的深入研究。从Wnt信号途径、涡虫wnt基因的种类及命名、涡虫wnt基因的表达及功能几方面对wnt基因在涡虫中的研究进展进行综述。     

透明颤菌血红蛋白基因表达对金色链霉菌生长代谢的影响

利用四环素抗性基因启动子在金色链霉菌中表达透明颤菌血红蛋白基因。在1m3发酵罐中研究了工程菌株的生长代谢特性。在溶解氧充足的条件下,透明颤菌血红蛋白表达,对金色链霉菌生长代谢未产生明显影响,工程菌株与参比菌株的生长代谢特性基本一致,工程菌株和参比菌株金霉素最终浓度分别为22905u/mL、22896u/mL。在低溶解氧条件下,透明颤菌血红蛋白的表达,可促进金色链霉菌菌体生长、菌丝活力保持和金霉素的合成：工程菌菌体浓度比参比菌株高5％～10％,产物合成提高11.4％。     

cDNA cloning and partial sequencing of homeobox genes in Dugesia japonica

In the freshwater planarian Dugesia japonica, four types of cDNAs of homeobox-containing genes have been isolated by screening a cDNA library using a homeobox guessmer. Partial sequencing analysis of two types of cDNAs revealed that one was a homolog of Dth2 which is a homeobox gene in Dugesia tigrina and another was similar to Distal-less gene in Drosophila. This suggests that planarians have many homeobox genes.     

Effect of weak and ultraweak combined magnetic fields and low-intensity microwaves on regeneration in the planarian <Emphasis Type="Italic">Dugesia tigrina</Emphasis>

Regeneration (blastema growth) in Dugesia tigrina was accelerated if prior to transection the planarians were exposed to a weak constant magnetic field (42 μT) combined with an ultraweak alternating magnetic field (40 nT, 3.7 Hz); lesser stimulation was obtained with weak microwaves (100 μW/cm² at 36 GHz). Field exposure after transection produced only half of the effect (magnetic field) or none at all (microwaves).     

A Family of Genes of Multidomain Free Lectins from a Planarian: Structure,Expression, and the Use as Markers for Monitoring Regeneration

A family of genes of the asexual race of planarian Girardia tigrina were described that encode proteins that belong to the superfamily of C-type lectins and were demonstrated to have a unique domain organization. The genes are differentially expressed in the planarian body. The protein products of at least two genes (scarf2 and gtlec1) are expressed in specifically differentiated gland cells of the planarian and secreted into the environment through long cell necks. A comparison of the results obtained by electron microscopy and immunohistochemistry with literature data allows the assignment of these cells to the group of adhesion glands. The observation of the regeneration of the cell necks in normal and artificial two-headed planaria indicated that the dorsoventral contact at the edge of the head part of the planarian body directs and maintains the growth of the gtLec1-producing cell necks during regeneration.     

Effect of timing of cutting on patterning and proportion regulation during regeneration of the planarian Dugesia tigrina

The time interval between cuts that are made to obtain a tissue fragment from a planarian was found to be important to the process of its regeneration. Short fragments made by two transverse cuts across the body were more likely to regenerate abnormally when the interval between the two cuts was 5 or 12 min than when it was 1.5 min. The longer intervals specifically altered the regression line in the correlation between the length:width ratio of fragments and frequency of abnormal regenerates. This effect occured regardless of which region of the body the fragment was taken from. The time interval also affected body proportioning in regenerates and to the greatest degree in fragments derived from the region located immediately behind the head. These results indicate that events occuring shortly after a cut is made in a planarian significantly affect structure patterning and proportioning of the regenerate.     

Position-specific and non-colinear expression of the planarian posterior (Abdominal-B-like) gene

Hox genes are pivotal molecules in the control of morphogenesis along the anterior-posterior (AP) axis in various bilaterians. Planarians are key animals for understanding the evolution of the bilaterian body plan. Furthermore, they are also known for their strong regeneration ability and are thought to use the Hox genes in the process of reconstruction of the AP axis. In the present paper, the identification and analysis of expression of two posterior (Abdominal-B-like) genes, DjAbd-Ba and DjAbd-Bb, is reported in the planarian Dugesia japonica. DjAbd-Ba is expressed in the entire tail region and its anterior boundary is the posterior pharyngeal region. In contrast, DjAbd-Bb is expressed in several types of cells throughout the body. During regeneration, the expression of DjAbd-Ba rapidly recovers a pattern similar to that in the normal worm. These findings suggest the possibility that DjAbd-Ba is involved in the specification of the tail region. The anterior boundary of the expression domain of the posterior gene DjAbd-Ba is anterior to the domains of the central genes Plox4-Dj and Plox5-Dj. These expression patterns of planarian Hox genes seem out of the rule of spatial colinearity and may reflect an ancestral feature of bilaterian Hox genes.     

Bromodeoxyuridine specifically labels the regenerative stem cells of planarians

The singular regenerative abilities of planarians require a population of stem cells known as neoblasts. In response to wounding, or during the course of cell turnover, neoblasts are signaled to divide and/or differentiate, thereby replacing lost cell types. The study of these pluripotent stem cells and their role in planarian regeneration has been severely hampered by the reported inability of planarians to incorporate exogenous DNA precursors; thus, very little is known about the mechanisms that control proliferation and differentiation of this stem cell population within the planarian. Here we show that planarians are, in fact, capable of incorporating the thymidine analogue bromodeoxyuridine (BrdU), allowing neoblasts to be labeled specifically during the S phase of the cell cycle. We have used BrdU labeling to study the distribution of neoblasts in the intact animal, as well as to directly demonstrate the migration and differentiation of neoblasts. We have examined the proposal that a subset of neoblasts is arrested in the G2 phase of the cell cycle by double-labeling with BrdU and a mitosis-specific marker; we find that the median length of G2 (approximately 6 h) is sufficient to account for the initial mitotic burst observed after feeding or amputation. Continuous BrdU-labeling experiments also suggest that there is not a large, slow-cycling population of neoblasts in the intact animal. The ability to label specifically the regenerative stem cells, combined with the recently described use of double-stranded RNA to inhibit gene expression in the planarian, should serve to reignite interest in the flatworm as an experimental model for studying the problems of metazoan regeneration and the control of stem cell proliferation.     

A novel invertebrate trophic factor related to invertebrate neurotrophins is involved in planarian body regional survival and asexual reproduction

Trophic factors are a heterogeneous group of molecules that promote cell growth and survival. In freshwater planarians, the small secreted protein TCEN49 is linked to the regional maintenance of the planarian central body region. To investigate its function in vivo, we performed loss-of-function and gain-of-function experiments by RNA interference and by the implantation of microbeads soaked in TCEN49, respectively. We show that TCEN49 behaves as a trophic factor involved in central body region neuron survival. In planarian tail regenerates, tcen49 expression inhibition by double-stranded RNA interference causes extensive apoptosis in various cell types, including nerve cells. This phenotype is rescued by the implantation of microbeads soaked in TCEN49 after RNA interference. On the other hand, in organisms committed to asexual reproduction, both tcen49 mRNA and its protein are detected not only in the central body region but also in the posterior region, expanding from cells close to the ventral nerve chords. In some cases, the implantation of microbeads soaked in TCEN49 in the posterior body region drives organisms to reproduce asexually, and the inhibition of tcen49 expression obstructs this process, suggesting a link between the central nervous system, TCEN49, regional induction, and asexual reproduction. Finally, the distribution of TCEN49 cysteine and tyrosine residues also points to a common evolutionary origin for TCEN49 and molluscan neurotrophins.     

Partial nitrification to nitrite using low dissolved oxygen concentration as the main selection factor

Partial nitrification to nitrite (nitritation) can be achieved in a continuous process without sludge retention by wash out of nitrite oxidising bacteria (NOB) while retaining ammonia oxidising bacteria (AOB), at elevated temperatures (the SHARON process) and, as demonstrated in this paper, also at low dissolved oxygen (DO) concentrations. Enriched AOB was attained at a low DO concentration (0.4 mg l⁻¹) and a dilution rate of 0.42 day⁻¹ in a continuous process. A higher oxygen affinity of AOB compared to NOB seemed critical to achieving this. This was verified by determining the oxygen half saturation constant, K _o, with similar oxygen mass transfer resistances for enriched AOB and NOB as 0.033 ± 0.003 mg l⁻¹ and 0.43 ± 0.08 mg l⁻¹, respectively. However, the extent of nitritation attained was found to be highly sensitive to process upsets.