1,721,016 research outputs found
Distribution of proliferating cells and vasa-positive cells in the embryo of Macrostomum lignano (Rhabditophora, Platyhelminthes)
No full textThe neoblast stem cell system of flatworms is considered to be unique within the animal kingdom. How this stem cell system arises during embryonic development is intriguing. Therefore we performed bromodeoxyuridine labelling on late stage embryos of Macrostomum lignano to assess when the pattern of proliferating cells within the embryo is comparable to that of hatchlings. This pattern can be found in late embryonic stages (stage 8). We also used the freeze cracking method to perform macvasa embryonic labelling. Macvasa is a somatic and germ line stem cell marker. We showed macvasa protein distribution during the whole embryonic development. In the macvasa-positive blastomeres the protein is localized around the nucleus in the putative chromatoid bodies. However, at a specific embryonic stage, it is also ubiquitously present in the cytoplasm of some blastomeres. We compare our data with what is known from Schmidtea polychroa of the expression of the vasa-like gene SpolvlgA and the protein distribution of the chromatoid body component Spoltud-1. The embryonic origin of the somatic stem cell system and the germ line is discussed
Distribution of proliferating cells and vasa-positive cells in the embryo of Macrostomum lignano (Rhabditophora, Platyhelminthes)
No full textThe neoblast stem cell system of flatworms is considered to be unique within the animal kingdom. How this stem cell system arises during embryonic development is intriguing. Therefore we performed bromodeoxyuridine labelling on late stage embryos of Macrostomum lignano to assess when the pattern of proliferating cells within the embryo is comparable to that of hatchlings. This pattern can be found in late embryonic stages (stage 8). We also used the freeze cracking method to perform macvasa embryonic labelling. Macvasa is a somatic and germ line stem cell marker. We showed macvasa protein distribution during the whole embryonic development. In the macvasa-positive blastomeres the protein is localized around the nucleus in the putative chromatoid bodies. However, at a specific embryonic stage, it is also ubiquitously present in the cytoplasm of some blastomeres. We compare our data with what is known from Schmidtea polychroa of the expression of the vasa-like gene SpolvlgA and the protein distribution of the chromatoid body component Spoltud-1. The embryonic origin of the somatic stem cell system and the germ line is discussed
Spermatogenesis and the structure of the testes in Isodiametra pulchra (Isodiametridae, Acoela)
No full textSpermatogenesis and the structure of the testes were studied ultrastructurally in Isodiametra pulchra (Smith and Bush, Transactions of the American Microscopical Society 1991; 110: 12; Hooge and Tyler, Journal of zoological systematics and evolutionary research 2005; 43: 100). The testes are paired, compact, non-follicular and lie dorsally and dorso-laterally to the paired ovaries, partially enfolding them. All stages of spermatogenesis, including spermiogenesis, are described at the ultrastructural level and their spatial organization within the testes is discussed. The cells at the early stages of spermatogenesis (spermatogonia and spermatocytes) are located on the dorsal and dorso-lateral sides of the testes, while the late stages (spermatids and filiform spermatozoa with 9+2 axonemes) lie at the ventral and inner periphery of the testes, adjacent to ovaries. All the cell types can be found both at the anterior and the posterior end of the testes. The value of the structure of the testes as a phylogenetic marker is addressed
From Stem Cell to Complex Sperm in the Rhabditophoran Macrostomum lignano
No full textMacrostomum lignano posesses a unique stem cell system (neoblasts) responsible for tissue-turnover growth, regeneration, and germ line formation. Its somatic gonads as well as the germ line formation in M.lignano. We mainly focused on the differentiation of primordial germ line stem cells to sperm using different techniques such as a light microscopical analysis and a transmission electron microscopic study mainly of the adult testis. 3D reconstructions were made based on TEM sections. The spermatozoa have a complex morphology with bristles, a terminal brush and an undulating shaft. It is still unclear how these morphological features develop. We found new intracellular structures associated with the bristles, which are transiently developed through spermiogenesis. Spermiogenesis of M. lignano will be discussed and compared to data on spermiogenesis in other species of Macrostomum and other platyhelminth taxa. More specifically, the developmental implications of bristle formation will also be discussed
From Stem Cell to Complex Sperm in the Rhabditophoran Macrostomum lignano
No full textMacrostomum lignano posesses a unique stem cell system (neoblasts) responsible for tissue-turnover growth, regeneration, and germ line formation. Its somatic gonads as well as the germ line formation in M.lignano. We mainly focused on the differentiation of primordial germ line stem cells to sperm using different techniques such as a light microscopical analysis and a transmission electron microscopic study mainly of the adult testis. 3D reconstructions were made based on TEM sections. The spermatozoa have a complex morphology with bristles, a terminal brush and an undulating shaft. It is still unclear how these morphological features develop. We found new intracellular structures associated with the bristles, which are transiently developed through spermiogenesis. Spermiogenesis of M. lignano will be discussed and compared to data on spermiogenesis in other species of Macrostomum and other platyhelminth taxa. More specifically, the developmental implications of bristle formation will also be discussed
In vivo prediction and discrimination of carcinogenic compounds using Schmidtea mediterranea's stem cell proliferation patterns
No full textAccurate and reliable carcinogenicity assays are imperative, as cancer risks are directly associated with the type and potency of a compound. A challenge for the development of alternative test methods is the prediction of non-genotoxic carcinogens, which entail different assessments of human cancer risk. The variety of non-genotoxic cancer pathways complicates the search for sensitive and reliable parameters expressing their carcinogenicity.
The presented assay enables a simple, rapid and inexpensive prediction and discrimination of both genotoxic and non-genotoxic carcinogens by means of flatworm stem cell dynamics. Our methodology entails an exposure to carcinogenic compounds during the animal's regeneration process, and the most striking differences between non-genotoxic and genotoxic carcinogen-induced proliferative responses were detected during the initial stages of the regeneration process, i.e. at the moment stem cells proliferate. We present a two-step-approach that combines in vivo adult stem cell proliferation patterns and phenotypic appearances. Based on the observed differences in stem cell dynamics we were able to discriminate between genotoxic and non-genotoxic carcinogens in a selected group of compounds (MMS, 4NQO, CsA, S-PB, MPH, CPZ). More specifically, genotoxic carcinogens were characterized by significantly fewer mitotic cells after 3 days exposure in comparison with a 1-day exposure set-up, while, on the contrary, non-genotoxic carcinogens were characterized by significantly more mitotic cells after 3 days exposure in comparison with a 1-day exposure set-up. The ability to discriminate between genotoxic and non-genotoxic compounds makes this approach unique and with significant added value to current research and drug development
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Use of freeze-cracking in ontogenetic research in Macrostomum lignano (Macrostomida, Rhabditophora)
Full text linkA method for studying whole mount flatworm
embryos based on freeze-cracking of the eggs is described.
This method allows successful immunohistological and
immunocytological studies of whole mount embryos. It does
not require the use of sharpened needles or a microinjection
system to puncture the eggshell. Moreover, this method is
more practical and less time-consuming than classical
puncturing and much cheaper than the use of a microinjection
system. The advantages of this method are illustrated by
results of several immunolocalisation experiments in the
macrostomid flatworm Macrostomum lignano. The optimal
procedure and crucial steps for this method are discussed
Ontogeny of the Complex Sperm in the Macrostomid Flatworm Macrostomum lignano (Macrostomorpha, Rhabditophora)
No full textSpermiogenesis in Macrostomum lignano
(Macrostomorpha, Rhabditophora) is described using
light- and electron microscopy of the successive stages in
sperm development. Ovoid spermatids develop to highly
complex, elongated sperm possessing an undulating distal
(anterior) process (or ‘‘feeler’’), bristles, and a proximal
(posterior) brush. In particular, we present a
detailed account of the morphology and ontogeny of the
bristles, describing for the first time the formation of a
highly specialized bristle complex consisting of several
parts. This complex is ultimately reduced when sperm
are mature. The implications of the development of this
bristle complex on both sperm maturation and the evolution
and function of the bristles are discussed. The
assumed homology between bristles and flagellae questioned
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