1,721,044 research outputs found
Chromosomal localization of a highly repeated EcoRI DNA fragment in Megoura viciae (Homoptera, Aphididae) by nick translation and fluorescence in situ hybridization
No full textTo investigate the genome of the aphid Megoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases. EcoRI digestion produced a highly repeated DNA fragment, about 600 bp long. The contribution of this EcoRI element to the total genome of M. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescent in situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained by in situ nick translation experiments carried out after EcoRI digestion, and clearly demonstrate that a substantial amount of M. viciae heterochromatin consists of EcoRI fragments which are mainly located on the X chromosome. Using the EcoRI restriction fragment as a molecular probe may prove to be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects
Chromatin Damage and Male Infertility
No full textThere is accumulating evidence linking sperm chromatin damage to poor reproductive outcome. The chromatin damage is associated to sperm anomalies that manifest themselves as breaks in the sperm nuclear DNA, aberrant ratios of protamine and histones in the chromatin, and the presence of apoptotic marker proteins in the ejaculated spermatozoa. This chapter examines the mechanisms involved in generating chromatin damage during spermatogenesis in the human, the techniques used to test sperm chromatin and how they may affect reproductive outcome, and how to reduce the risk of using spermatozoa with chromatin damage
NORs heteromorphism within a parthenogenetic lineage of the aphid Megoura viciae
No full textIn parthenogenetic females of a clone of the aphid Megoura viciae (Homoptera, Aphididae), more than 50% of the cells show heteromorphism between homologous NORs which are located on one telomeric region of the two X chromosomes. Using different techniques, such as staining with the CG-specific fluorochrome chromomycin A(3), silver staining and in-situ hybridization with an rDNA probe, we have shown that the observed heteromorphism is due to an unequal distribution of ribosomal genes between homologous NOR regions. The total number of rDNA genes per individual aphid remained constant. Moreover, the analysis of cells from single embroys has shown that the observed heteromorphism is not only intraclonal but also intraindividual. These data, together with the finding of X chromosomes connected by chromatin bridges between their NORs, allow us to suggest that mitotic unequal crossing over could be the main cause of NOR heteomorphism in this taxon
Characterization of equine amnion-derived Mesenchymal Stem Cells (MSCs) after cryopreservation
No full textLocalizzazione dei peptidi "CDC" nel mollusco bivalve Venus verrucosa.
No full textE' stao effettuato uno screening immunocitochimico che ha dimostratyo la presenza nel sistema nervoso gangliare del bivalve Venus di alcuni neurotrasmettitori e neuropeptidi, come i peptidi "CDC" implicati nel comporatamento riproduttivo dei gasteropodi e di altri bivalvi
Mechanisms of environmental reproductive toxicity: Sperm DNA damage
No full textThe spermatogenetic process in the human produces a heterogeneous cell population showing different degrees of maturation, variable morphological features and fertilizing capacity. There is a large body of evidence that some of the ejaculated spermatozoa possess a variety of abnormalities at the nuclear, cytoskeletal, and organelle levels and that these anomalies impact fertility. Damage of sperm DNA or its chromatin structure can occur at any step of whole spermatogenesis and could have endogenous (i. e. pathological altered germ cell maturation) or exogenous origin (i. e. exposure to xenobiotic substances). Three main theories have been proposed to explain DNA anomalies in the ejaculated human spermatozoa (Sakkas and Alavarez, 2010). The first theory supports that DNA damage in mature spermatozoa is associated with poor chromatin packaging or abnormal packing due to underprotamination and/or alteration of Topisomerase II activity which results in the presence of endogenous nicks in DNA (Manicardi et al., 1995). The second theory proposes that sperm DNA damage could be related to a process called “abortive apoptosis” whereby sperm cells are earmarked for apoptosis during spermatogenesis but survive to be present in the ejaculate (Sakkas et al., 2002). A major factor affecting sperm is also their vulnerability to oxidative stress, because they are deficient in both antioxidant and DNA-repair systems and rich in targets for oxidative attack (Aitken et al., 1998). The correct DNA packaging and stability appears to be fundamental for the protection against both endogenous and exogenous DNA damage. Transmission of damaged DNA to the offspring, particularly at levels that exceed the DNA repair capacity of the oocyte, has been shown to have serious consequences in animal models and is also being more and more implicated in the human. Normal sexual development, differentiation and function in the human has been shown to be altered by the presence of synthetic chemicals in the environment acting as endocrine disruptors or mutation agents. Moreover, exposure to physical agents or chemicals, including therapeutic drugs and environmental toxicants, either individually or together, can affect the integrity of sperm chromatin (Stronati et al., 2006). The observation that ejaculated human spermatozoa possess DNA damage raises numerous problems relating to why and how these spermatozoa arise in the ejaculate of some men and what consequences they have if they succeed in their genetic project. Understanding the mechanisms responsible will improve our knowledge about certain causes of male infertility
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
Occurrence of NORs heteromorphism in the two X chromosomes of different aphid species
No full textIn this paper we review recent work concerning both cytogenetic and molecular features of constitutive heterochromatin in the holocentric chromosomes of different aphid species. Sections include an extensive survey regarding chromosomal localization and DNA base composition of C-positive areas together with a cytological and molecular analysis of nucleolar organizer regions. The possible role of mitotic crossing over on genetic variability in parthenogenetic lineages is also briefly reviewed
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