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Lipovitellins and Phosvitins in the laid fertilized eggs during incubation of the oviparous lizard Podarcis sicula
No full textLipovitellins and Phosvitins in the laid fertilized eggs during incubation of the oviparous lizard Podarcis sicula
No full textVitellogenin precursors in the liver of the oviparous lizard Podarcis sicula.
No full textCAMERINO ITAL
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
Le componenti proteiche del tuorlo della lucertola Podarcis sicula durante lo sviluppo embrionale.
No full text
Vitellogenin precursors in the liver of the oviparous lizard Podarcis sicula.
No full textCAMERINO ITAL
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
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
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