Introduction au Développement Embryonnaire

Study Notes

The document discusses the process of fertilization and the initial stages of embryonic development.
It details the different phases of embryonic development, from the initial interactions between sperm and egg to the division and differentiation of cells.
The stages of development, such as the establishment of the zygote, the formation of pronuclei, and completion of meiosis, are key components.

The activation of the oocyte has a dual purpose: triggering oocyte metabolism and preventing polyspermy (multiple sperm entrance).
The activation occurs in a chronological order starting with calcium mobilization, followed by cortical granule exocytosis, followed by the completion of the second meiotic division.

The release of cortical granules is a crucial step for preventing polyspermy.
This process alters the zona pellucida (ZP), preventing further sperm penetration.

Completion of the second meiotic division results in the oocyte developing into an ovotide.
The expulsion of the second polar body helps set down a final stage of meiosis.

The study notes on molecular mechanisms highlight the role of molecules like cyclin B and securin are regulated.
These proteins prevent the separation of chromatids during the progression of meiosis and ultimately the process of mitosis.

This stage involves the fusion and condensation of the sperm and oocyte nuclei. These nuclei are called pronuclei.
Following formation, they start their development, their ultimate aim being the fusion.

A final step after the pronuclei formation is the contact or fusion of the pronuclei.
This process marks the beginning of the fusion of the genomes, culminating in the zygote, diploid, and 2n cell phase.

The first mitotic division begins.
The chromosomes begin to group up for the preparation of the first embryonic division.
The formation of the zygote involves the merging of the maternal and paternal sets of chromosomes.

Triploidy (3n): A non-viable condition due to a meiotic abnormality, resulting in spontaneous abortion in mammals.
Chimera: A condition where an individual has two separate genetic populations of cells.
Androgenesis/Molar Pregnancies: Development from a sperm only, leading to placental tissue growth and no embryonic tissue.
Parthenogenesis/Ovarian Cyst: Embryonic development initiated by the egg without sperm fertilization, producing a cyst with diverse tissues.

The concept of genomic imprinting emphasizes that an individual's genome is not symmetrical.
The origin of the gene affects the function.
The examples demonstrated show that the origin of different parent-derived genes is a factor for their expression.

Imprinting, is achieved through epigenetic modifications, which impact gene expression without altering the DNA sequence.
The modifications include DNA methylation patterns, histone modifications, etc.