Spermatogenesis Flashcards
What is spermatogenesis?
This is when spermatogoniums (diploid sperm cells) become many spermatozoa (haploid sperm cells) through meiosis
What is the process of a spermatogenesis from spermatogonium to spermatozoan?
Spermatogonium undergoes mitosis to become spermatocytes. These spermatocytes become spermatids after undergoing meiosis. These differentiate to become spermatozoan.
What are the undifferentiated spermatogonia and differented spermatogonia found in humans, primates and mice?
Humans = AD can self renew or become AP. AP can either self renewal or differentiate into B.
Primates = AD can self renew or become AP. AP can either self renewal or differentiate into B1. This then goes onto become B2, B3 and finally B
Mice = AS can either self renew or differentiate in APR which can self renewal or differentiate into Aal. Aal either self renews or differentiates into A1. Then becomes, A2, A3, A4, In, before settling as B.
What is the spermatogonial stem cell niche?
A specialised physical and chemical environment which controls if there cell differentiates or self-renewals.
How does spermatogonia self renewal get signalled?
There are 3 paracrine signals (FGF2, CXCL12, GDNF) delivered from surrounding cells (leydig, sertoli etc) which can react with receptors on the spermatogonia to make them self renew.
Where is GNF produced from and what is this essential for?
Peritubular Myeloid Cells and are needed for SSC self renewal
How do spermatogonia differentiate?
Retenoic acid is secreted from surrounding cells such as sertoli cells . This is produced after puberty and when they have developed enough retenoic acid they will differentiate.
What are the two ways retinoic acid can differentiate spermatogonia and what are the products of this?
Genomic and non-genomic pathway.
After retinoic acid binds the genomic pathway causes the transcription of Stra8.
Once retinoic acid binds to the non-genomic pathway KIT is translated.
Both KIT and Stra8 start meiosis
How does each spermatogonium know if it is going to self renew or differentiate?
Their proximity to the niche which affects the availability of mitogens.
What are male germ cells undergoing meiosis called?
Spermatocytes
How does meiosis happen?
The 46 chromosomes in the cell pair up to create 23 pairs of homologous chromosomes.
Each individual chromosome replicates to form sister chromatids joined at a centromere. The homologous chromosomes exchange genes in a crossing over event before lining up in the centre of the cell and the homologous chromosomes pulled apart (sister chromosomes are still kept together) and the cytoplasm divides creating 2 cells.
Then the sister chromatids line up along the equator and are pulled apart, the cytoplasm then splits into 2 more cells.
You now have a net total of 4 cells.
How do the germ cells attach and move? (Germ-sertoli cells and sertoli-sertoli cells).
Germ-sertoli cell adherens junctions break and reform to support the movement of the cells.
Sertoli-sertoli cells have tight junctions which form the blood testes barrier. There is unzipping of this barrier during spermatocyte transit.
Why do you need a blood tests barrier?
To protect the spermatocytes who have completed meiosis from the immune system and they will be recognised as foreign and destroyed.
What is essential for progression through meiosis?
Androgens
Destruction of leydig cells using ethane dimethane sulphonate causes reduction in interstitial testosterone which causes the degeneration of spermatogenesis.
What is spermiogenesis and what changes here?
Germ cells remodelling.
The condensation of the cytoplasm
The acrosome and tails are formed.
DNA compaction
Cytoplasmic storage of mRNAs required for future translation
