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Fertilisation - Anatomy & Physiology (view source)
Revision as of 07:31, 4 July 2008
, 07:31, 4 July 2008→Formation of Pronuclei
== Formation of Pronuclei ==
== Formation of Pronuclei ==
After the sperm nucleus enters the Oocyte it becomes the '''male pronucleus'''. Before this can occur, the sperm nucleus must undergo marked changes within the Oocyte cytoplasm.
* Disulphide cross-links render the nucleus almost inert. This is important when exposed to the hostile environment of the female tract during transport and also on penetration through the Zona Pellucida.
* In the Oocyte cytoplasm, the nucleus must '''decondense''' in order for male and female chromosomes to pair.
* Disulphide cross-links are rapidly reduced in the Oocyte cytoplasm primarily by '''Glutathione'''.
== Syngamy ==
* Male and female pronuclei fuse.
* Sperm delivers a haploid complement of chromosomes, but also activates the Oocyte by:
** A unique '''phospholipase Cζ''' causes release of calcium from the endoplasmic reticulem to the cytosol. This is then re-sequestered and bound in the endoplasmic reticulem to give regular 'spikes' or oscillations of calcium that signal rapidly across the Oocyte. The calcium signal activates the Oocyte from meiotic arrest.
** Provides the '''centriole''' contribution to initial cell division, allowing formation of the two-celled embryo.
''N.B: Although sperm mitochondria enters the Ooctye cytoplasm, they carry a ubiquitin signal. They are subsequently destroyed by Ubiquiitinase and do NOT contribute to mitochondrial DNA. Therefore mitochondial DNA is entirely from the maternal side.''