Fertilization marks the end of oogenesis and the beginning of embryogenesis. The legacy of oogenesis is, however, maintained by virtue of the stored nutritional and regulatory molecules that fuel, and in many cases direct, early development. The signal that stimulates the transition from oocyte to embryo is a sperm-induced increase in the concentration of intracellular free Ca2+. Thus successfu...

Bicaudal-D (Bic-D) is essential for the establishment of oocyte fate and subsequently for polarity formation within the developing Drosophila oocyte. To find out where in the germ cells Bic-D performs its various functions we made transgenic flies expressing a chimeric Bic-D::GFP fusion protein. Once Bic-D::GFP preferentially accumulates in the oocyte, it shows an initial anterior localization ...

In vivo, histone H1 plays an active role in establishing the transcriptionally repressed chromatin state of the oocyte-type 5S RNA genes in the early stages of Xenopus development. By using fully defined in vitro system of chromatin assembly on plasmids with cloned oocyte- or somatic-type 5S gene repeats we found that the oocyte repeat which comprises a 120 bp oocyte-type 5S RNA gene placed wit...

In mammals, immature oocytes are surrounded by a layer of flattened cells. At this early stage of development, these "follicle cells" and the plasma membrane of the oocyte are in close proximity. As the oocyte matures, the follicle cells multiply and become cuboidal or radially elongated, and a jelly-like substance containing polysaccharides (1) appears between the oocyte cortex and the follicl...

In the present study, various developmental stages of Liza aurata oocyte, especially IV and V stages have been described. On the basis of histological investigations, oocyte development in L. aurata comprises immature (I), the early maturing (II), the late maturing (III), mature (IV), ripe (V), and spent (VI) stages. In the stages I and II, nucleus occupied large volume of oocyte. Vacuolization...

It is known that amphibian oocytes undergo maturation through the formation and activation of maturation-promoting factor (MPF) in response to stimulation by the maturation-inducing hormone progesterone; however, the signal transduction pathway that links the hormonal stimulation on the oocyte surface to the activation of MPF in the oocyte cytoplasm remains a mystery. The aim of this study was ...

Vitrification method is widely used in oocyte cryopreservation for IVF but the birth rates are lower than that of the fresh oocyte. One of the known main reasons is structural instability of meiotic spindle and chromosome systems of mature oocyte. To get the best way for keeping competence of matured oocytes, we studied the best conditions for vitrification focused on equilibration times. The m...

During mammalian oocyte maturation there are marked changes in the distribution of mitochondria that supply the majority of the cellular ATP. Such redistribution of mitochondria is critical for oocyte quality, as oocytes with a poor developmental potential display aberrant mitochondrial distribution and lower ATP levels. Here we have investigated the dynamics of mitochondrial ATP production thr...

Xenopus laevis tadpoles and toads were killed at several ages. The structure of the nuclei of the germinal cells has been observed by light and electron microscopes. We distinguish 11 successive stages in nucleolar structure: (1) a single, essentially granular nucleolus in the oogonium (10 /tm diameter), (2) a reticulated nucleolus in the leptotene oocyte, (3) fragmentation of this nucleolus in...

Egg activation is the process by which a mature oocyte becomes capable of supporting embryo development. In vertebrates and echinoderms, activation is induced by fertilization. Molecules introduced into the egg by the sperm trigger progressive release of intracellular calcium stores in the oocyte. Calcium wave(s) spread through the oocyte and induce completion of meiosis, new macromolecular syn...