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Yolk Proteins in Vertebrate: A Review
No full textIn all the oviparous vertebrates, also showing different
reproductive modes, that is, oviparity, ovoviviparity,
and viviparity, the oocytes always contain yolk proteins
that represent the nourishment store for the developing
embryo. Yolk proteins derive from the cleavage of a large
maternal serum lipoglycophosphoprotein called vitellogenin
(VTG) produced by the liver under estrogen
stimulation (Wallace, 1985 and references therein;
Rosanova et al., 2002). The mammalian (eutherian)
liver lost the ability tomakeVTGbut the genetic bases of
this acquired inability are still unknown (Rothchild,
2003).
Once synthesized by the liver, VTG reaches the
ovarian follicles through the bloodstream, crosses between
the granulosa cells and is incorporated into
the oocytes by micropinocytosis, a mechanism of
receptor-mediated endocytosis (Opresko and Wiley,
1987; Schneider, 1996; Romano and Limatola, 2000).
VTG internalization occurs in coated pits of the oocyte
plasma membrane; they rapidly detach and give rise to
coated vesicles in the cortical oocyte cytoplasm; the
latter rapidly lose their clathrin coat and coalesce to
form the primordial yolk globules subsequently transformed
into yolk platelets (Ghiara et al., 1968, 1970;
Neaves, 1972; Wallace, 1985; Limatola and Filosa,
1989). Similar ultrastructural features were described
also in the mosquito oocytes (Roth and Porter, 1964).
In the platelets, VTG are enzymatically cleaved in
lipovitellins and phosvitins that represent the two
principal classes of yolk proteins. Lipovitellins are high
molecular-weight proteins with a strongly hydrophobic
nature; phosvitins show a lower molecular weight and
are highly phosphorylated. The cleavage of VTG in yolk
proteins is generally indicated as primary degradation;
furthermore, in almost all vertebrates studied, a secondary
degradation of yolk proteins occurs at oocyte
maturation or later during embryo development.
This review represents an attempt to summarize the
numerous data of the literature about the VTG derived
yolk proteins during the oogenesis and their utilization
during the embryogenesis
LIPOVITELLINS AND PHOSVITINS IN THE LAID FERTILIZED EGGS DURING INCUBATION OF THE OVIPAROUS LIZARD PODARCIS SICULA
No full textYolk Proteins in Vertebrate: A Review
No full textIn all the oviparous vertebrates, also showing different
reproductive modes, that is, oviparity, ovoviviparity,
and viviparity, the oocytes always contain yolk proteins
that represent the nourishment store for the developing
embryo. Yolk proteins derive from the cleavage of a large
maternal serum lipoglycophosphoprotein called vitellogenin
(VTG) produced by the liver under estrogen
stimulation (Wallace, 1985 and references therein;
Rosanova et al., 2002). The mammalian (eutherian)
liver lost the ability tomakeVTGbut the genetic bases of
this acquired inability are still unknown (Rothchild,
2003).
Once synthesized by the liver, VTG reaches the
ovarian follicles through the bloodstream, crosses between
the granulosa cells and is incorporated into
the oocytes by micropinocytosis, a mechanism of
receptor-mediated endocytosis (Opresko and Wiley,
1987; Schneider, 1996; Romano and Limatola, 2000).
VTG internalization occurs in coated pits of the oocyte
plasma membrane; they rapidly detach and give rise to
coated vesicles in the cortical oocyte cytoplasm; the
latter rapidly lose their clathrin coat and coalesce to
form the primordial yolk globules subsequently transformed
into yolk platelets (Ghiara et al., 1968, 1970;
Neaves, 1972; Wallace, 1985; Limatola and Filosa,
1989). Similar ultrastructural features were described
also in the mosquito oocytes (Roth and Porter, 1964).
In the platelets, VTG are enzymatically cleaved in
lipovitellins and phosvitins that represent the two
principal classes of yolk proteins. Lipovitellins are high
molecular-weight proteins with a strongly hydrophobic
nature; phosvitins show a lower molecular weight and
are highly phosphorylated. The cleavage of VTG in yolk
proteins is generally indicated as primary degradation;
furthermore, in almost all vertebrates studied, a secondary
degradation of yolk proteins occurs at oocyte
maturation or later during embryo development.
This review represents an attempt to summarize the
numerous data of the literature about the VTG derived
yolk proteins during the oogenesis and their utilization
during the embryogenesis
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
LE COMPONENTI PROTEICHE DEL TUORLO DELLA LUCERTOLA PODARCIS SICULA DURANTE LO SVILUPPO EMBRIONALE
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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