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  • 1
    ISSN: 1432-1432
    Keywords: Key words: 18S rDNA — Polymorphism — Dugesiidae — Platyhelminthes — Variability — Multigene family — Metazoan — Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Analysis of the 18S rDNA sequences of five species of the family Dugesiidae (phylum Platyhelminthes, suborder Tricladida, infraorder Paludicola) and eight species belonging to families Dendrocoelidae and Planaridae and to the infraorder Maricola showed that members of the family Dugesiidae have two types of 18S rDNA genes, while the rest of the species have only one. The duplication event also affected the ITS-1, 5.8S, ITS-2 region and probably the 28S gene. The mean divergence value between the type I and the type II sequences is 9% and type II 18S rDNA genes are evolving 2.3 times more rapidly than type I. The evolutionary rates of type I and type II genes were calibrated from biogeographical data, and an approximate date for the duplication event of 80–120 million years ago was calculated. The type II gene was shown, by RT-PCR, to be transcribed in adult individuals of Schmidtea polychroa, though at very low levels. This result, together with the fact that most of the functionally important positions for small-subunit rRNA in prokaryotes have been conserved, indicates that the type II gene is probably functional.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 364 (1993), S. 109-109 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Robertson reports1 the presence of different families of mariner transposon elements2 in many insects using a polymerase chain reaction (PCR) strategy and degenerated oligonucleotides from conserved sequences of the mariner central region. The presence of different subfamilies in the same ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 415 (2002), S. 13-13 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sir In your timely, engaging and well-illustrated News Feature “The regeneration gap” (Nature 414, 388–390; 2001), you report on the often-neglected invertebrate models of regeneration, such as ...
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  • 4
    ISSN: 1432-041X
    Keywords: Key words Planaria ; Pattern formation ; Pharynx regeneration ; Cell renewal ; Monoclonal antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The special morphological features of freshwater planarians make them an attractive and informative model for studying the processes of regeneration and pattern formation. In this work, we investigate pattern formation and maturation of the planarian pharynx during regeneration in tail fragments. Using three monoclonal antibodies (TCAV-1, TF-26 and TMUS-13) specific for epithelial, secretory and muscle cells, respectively, we followed the sequence and timing of differentiation and maturation of these three cell types within the regenerating pharynx. Two of these monoclonal antibodies, TCAV-1 and TMUS-13, also labelled morphologically immature cells that appear to be committed to the differentiation pathway leading to their respective adult cell types. Our results show that the cells forming the new pharynx come from undifferentiated cells through proliferation and differentiation processes rather than from differentiated cells of the old stump. We describe three stages of pharynx regeneration according to the immunoreactivity shown: (1) no immunoreactivity, corresponding to the accumulation of undifferentiated cells that form the pharynx primordium; (2) immunoreactivity to TCAV-1 and TMUS-13, corresponding to the re-building of the pharynx; and (3) immunoreactivity to TF-26, corresponding to a fully mature and functional pharynx. The sequence of differentiation of these three cell types suggests that the pharynx grows by intercalation of new undifferentiated cells coming from the parenchyma between the older pharyngeal cells, in agreement with existing models of pharynx regeneration. Finally, our results suggest an intercalary model for pharynx epithelial cell renewal.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 194 (1985), S. 364-368 
    ISSN: 1432-041X
    Keywords: Intercalary regeneration ; Chromosomal marker ; Distal and proximal transformation ; Chimaeras ; Planarians
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Studies on intercalary regeneration in several organisms have shown that a regenerate is formed when surfaces of different positional value along the proximo-distal axis are opposed. One of the main problems posed by this phenomenon is to know which piece contributes to the building of the regenerate. In the present work we have studied this problem in planarians using chimaeras made between pieces of different body levels, irradiated or not, of the sexual and asexual races ofDugesia(S)mediterranea that differ in a chromosomal marker. The results found show very clearly that intercalary regenerates in planarians are formed by cells coming from both pieces (stumps), and that irradiated pieces keep the positional values and interact with non-irradiated pieces to restore the missing parts. This means that distal and proximal transformation do actually occur at the same time during intercalary regeneration in planarians. The implications of these results as regards to the origin of cells in the regenerate and to present models of intercalary regeneration are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Histochemistry and cell biology 107 (1997), S. 139-149 
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  To obtain specific immunological probes for studying molecular mechanisms involved in cell renewal, cell differentiation, and pattern formation in intact and regenerating planarians, we have produced a hybridoma library specific for the asexual race of the freshwater planarian Dugesia (Girardia) tigrina. Among the 276 monoclonal antibodies showing tissue-, cell-, cell subtype-, subcellular- and position-specific staining, we have found monoclonal antibodies against all tissues and cell types with the exception of neoblasts, the undifferentiated totipotent stem-cells in planarians. We have also detected position-specific antigens that label anterior, central, and posterior regions. Patterns of expression uncovered an unexpected heterogeneity among previously thought single cell types, as well as interesting cross-reactivities that deserve further study. Characterization of some of these monoclonal antibodies suggests they may be extremely useful as molecular markers for studying cell renewal and cell differentiation in the intact and regenerating organism, tracing the origin, lineage, and differentiation of blastema cells, and characterizing the stages and mechanisms of early pattern formation. Moreover, two position-specific monoclonals, the first ones isolated in planarians, will be instrumental in describing in molecular terms how the new pattern unfolds during regeneration and in devising the pattern formation model that best fits classical data on regeneration in planarians.
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  • 7
    ISSN: 1573-5117
    Keywords: Monoclonal antibodies ; regeneration ; immunohistochemistry ; pharyngeal epithelial cells ; differentiation ; Dugesia (G.) tigrina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During regeneration in planarians, anterior (head and prepharyngeal) and posterior (postpharyngeal and tail) fragments rebuild one of the most peculiar structures of planarians: the pharynx and the pharynx cavity. Previous studies (see Brønsted, 1969, for a general review, and Asai, 1990, 1991, for anterior regeneration) have shown that within postpharyngeal pieces both structures appear in the old stump from clusters of undifferentiated cells. However, the lineage and differentiation of their elements (inner and outer epithelial cells, muscle layers, gland cells, nerve rings) and the overall pattern of growth and differentiation is not clear.
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  • 8
    ISSN: 1573-5117
    Keywords: Turbellaria ; Dugesia ; homeobox ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To identify potential pattern control and cell determination and/or differentiation genes in the freshwater planarian Dugesial (G.) tigrina, we searched for homeobox genes of different types in the genome of this primitive metazoan. We applied two basic approaches: 1) Screening the cDNA library with degenerate oligonucleotides corresponding to the most conserved amino acid sequence from helix-3 of the homeodomain of each family; and 2) PCR amplification of genomic DNA or cDNA, using two sets of degenerated oligonucleotides corresponding to helices 1 and 3 of the homeodomain or two specific domains of the POU family. Using the first strategy we have identified and characterized two tissue-specific cell determination and/or differentiation NK-type homeobox genes. Using the second strategy we have identified several homeobox genes that belong to the HOM/Hox, paired (prd) or POU families.
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  • 9
    ISSN: 1573-5117
    Keywords: monoclonal antibodies ; regional antigen ; regeneration ; pattern formation ; immunohistochemistry ; Dugesia (G.) tigrina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have produced monoclonal antibodies (mAbs) against antigens of the freshwater planarian Dugesia (G.) tigrina (Girard) using standard protocols. One of these mAbs, TCEN-49, detects an antigen (TCEN-49Ag) present in most cells of the central area of the body, including the pharynx. Labelled cells seem more related by position than by lineage, suggesting that TCEN-49Ag is involved somehow in the expression of central body positional identity. The spatial and temporal changes in TCEN-49Ag expression during growth/degrowth and regeneration have been monitored and the implications of these results are discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 383 (1998), S. 189-190 
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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