Considerations on the neoblasts of planarians on the basis of certain karyological evidence

Benazzi, Mario

doi:10.1007/bf00332791

Cited by 15 publications

(5 citation statements)

References 9 publications

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“…Incorporation studies with bromodeoxyuridine (BrdU) show that 99% of the neoblasts are labeled with BrdU after three days of continuous BrdU treatment. Thus, there is no evidence supporting a slowly-cycling subpopulation of neoblasts [Benazzi, 1966;Newmark and Sanchez Alvarado, 2000;Reddien and Sanchez Alvarado, 2004]. Although BrdU incorporation was not utilized in this study, labeling with BrdU might be used to assure that only first division metaphases were being scored for CAs, possibly decreasing the variability in the responses.…”

Section: Discussionmentioning

confidence: 99%

“…The planarians were irradiated during the regeneration process, 48 hr after cutting, and the chromosomes were prepared 24 hr later. The regenerating tissue is formed by a permanent population of stem cells [Benazzi, 1966;Newmark and Sanchez Alvarado, 2000;Sanchez Alvarado and Kang, 2005], which migrate to the wound to form a totipotent embryonic tissue resembling a syncytium [Chandebois, 1972[Chandebois, , 1973, called the new blastema. The highest mitotic Environmental and Molecular Mutagenesis.…”

Section: Discussionmentioning

confidence: 99%

“…Planarians have a high regeneration capacity. When an individual is cut into several parts, each part regenerates into a complete organism containing fully functional organs [Chandebois, 1965;Benazzi, 1966;Newmark and Sanchez Alvarado, 2000;Sanchez Alvarado and Kang, 2005]. The regenerating tissues have a high mitotic index.…”

Section: Introductionmentioning

confidence: 99%

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Freshwater planarians as novel organisms for genotoxicity testing: Analysis of chromosome aberrations

Lau

Knakievicz

Prá

et al. 2007

Environ and Mol Mutagen

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Two freshwater species of planarians, Girardia schubarti Marcus and G. tigrina Girard, were used for measuring chromosome aberration (CA) induction under laboratory conditions. Three genotoxicants were tested: methyl methanesulfonate (MMS), a direct-acting genotoxicant; cyclophosphamide, a metabolism-dependent genotoxicant; and gamma-radiation, a clastogenic agent. All three agents produced positive responses in both species. The strongest dose-responses were detected with MMS, and, in general, G. tigrina was somewhat more sensitive to the genotoxicity of the agents than G. schubarti. This difference in sensitivity may be due to: (a) the smaller body mass of G. tigrina; (b) differences in DNA repair, which may be reflected in the marginally higher background CA frequency of G. tigrina; and/or (c) the greater number of chromosomes in G. tigrina (2N = 16) as compared with G. schubarti (2N = 8). The responses induced by gamma-radiation in the planarians were similar to or higher than those induced in cultured human lymphocytes. The CA-planarian assay has advantages for monitoring environmental genotoxicity in natural water resources or urban and industrial wastewater since planarians are characterized by (a) a relatively low number of easily analyzable chromosomes; (b) high regenerating capacity, allowing exposure of replicating cells from different parts of the same organism to different doses; (c) easy maintenance under laboratory conditions; and (d) worldwide distribution, making them available for genotoxicity tests using either in situ or controlled laboratory exposure conditions.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Freshwater planarians as novel organisms for genotoxicity testing: Analysis of chromosome aberrations

Lau

Knakievicz

Prá

et al. 2007

Environ and Mol Mutagen

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“…Abbiamo impiegato per i nostri esperimenti esemplari di Dugesia lugubris appartenenti a quattro diversi biotipi caratterizzati da differenti gradi di ploidia (BENAZZI, 1957. La nostra indagine e stata facilitata dal fatto che questi animali vengono normalmente allevati in laboratorio e all'epoca della maturita presentano contemporaneamente nei loro germigeni ovociti in diversi stadi di accrescimento.…”

Section: Material£ E Tecnicaunclassified

“…Nella estesissima e complessa letteratura sulle Planarie non esistono ricerche su questo argomento, anche se non mancano alcune osservaziom nguardanti le dimensioni degli ovociti di Dugesia lugubris (MIROLLI, 1956) eseguite nei differenti biotipi che BENAZZI ( 1957) ha distinto nell'ambito della stessa specie.…”

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Osservazioni Citometriche Sugli Elementi Germinali Dell'Ovario in Quattro Diversi Biotipi Della PlanariaDugesia Lugubris

Grasso

Zaccanti

1968

Caryologia

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A contribution to the problem of the origin of the blastema cells in planarians: A karyological and ultrastructural investigation

Gremigni

Puccinelli

1977

J. Exp. Zool.

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The basic problem in Planarian regeneration, i.e., the origin of blastema cells, has been tackled by means of a karyological investigation carried out on a triplo-hexaploid biotype of Dugesia lugubris. The main characteristic of this biotype is that male germ cells are karyologically distinguishable from female germ cells and from the somatic cells.Sexually mature specimens were transected at a caudal level, posterior to the testes: from each transected specimen two regenerants were obtained, both of which formed a blastema. Thirty-six hours after the transection most of the metaphase cells of the anterior regenerant blastema (a.r.b.1 had 12 chromosomes. However, cells with 8 chromosomes as well as cells showing signs of chromosome elimination were also present. Three days after the transection only cells with 8 or 12 chromosomes could be detected in the a.r.b.The ultrastructural examination of the 36-hours-old a.r.b. revealed that some blastema cells display features which can be interpreted as indicating a process of dedifferentiation, the others being virtually undifferentiated. In the posterior regenerant blastema (p.r.b.1 of sexually mature specimens only cells with 12 chromosomes were present. The same applies to both the a.r.b. and p.r.b. of sexually immature specimens and to developing embryos. These findings suggest that in the sexually mature planarians studied, the blastema is formed mainly by triploid cells. However, in those regenerants which still possess testes, immature male germ cells can also contribute to the blastema formation. The possible role played by these male germ cells in the reconstitution of the missing tissues in the biotype studied is also discussed.One of the major problems in planarian regeneration concerns the nature and the origin of the cells which form the blastema. As is well known, the process by which the blastema is formed is currently explained according to two main theories. Several authors (cf., Wolff and Dubois, '47; Dubois, '49; Lender, '62; Brsndsted, '69) maintain that neoblasts -pluripotent, embryonic cells dispersed throughout the animal body -are the sole cell type responsible for regeneration. On the other hand, other workers (Steinmann, '08; Lang, '12; Hyman, '51; Woodruff and Burnett, '65; Rose and Shostak, '68; Hay, '68; Coward, '69) believe that, as a result of a regenerative stimulus, many specialized cells can J. EXP. ZOOL., dedifferentiate and migrate to the wounded region where they form the blastema. The missing tissues would then be reconstituted by redifferentiation of the dedifferentiated cells.Evidence obtained from several lines of experiment (for a recent survey on the subject, see Brsndsted, '69; Pedersen, '72; Gremigni, '74; Chandebois, '76) do not yet allow reconciliation of these two conflicting theories. It is possible that the mechanisms adduced by the two quoted theories to explain the formation of the blastema, i.e., the involvement of embryonic reserve cells or the dedifferentiation

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Considerations on the neoblasts of planarians on the basis of certain karyological evidence

Cited by 15 publications

References 9 publications

Freshwater planarians as novel organisms for genotoxicity testing: Analysis of chromosome aberrations

Freshwater planarians as novel organisms for genotoxicity testing: Analysis of chromosome aberrations

Osservazioni Citometriche Sugli Elementi Germinali Dell'Ovario in Quattro Diversi Biotipi Della PlanariaDugesia Lugubris

A contribution to the problem of the origin of the blastema cells in planarians: A karyological and ultrastructural investigation

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