L9: Spermatogenesis Flashcards
What are the key phases in spermatogenesis?
- Proliferation of spermatogonia (one spermatogonium –> many spermatozoa)
- Generation of genetic diversity by meiosis (Diploid spermatogonia –> haploid, genetically diverse spermatozoa) – beneficial because introduces genetic diversity to offspring
- spermiogenesis (round spermatogonia –> tadpole-shaped spermatozoa)
Describe differences between spermatogonia, spermatocytes, spermatids, spermatozoan
- spermatogonium – diploid stem cells
- spermatocytes – spermatogonium after mitosis
- Spermatids – spermatocytes at meiosis divide into 4 haploid spermatids
- Spermatozoan – differentiated spermatid
Where does spermatogenesis take place?
Spermatogenesis proceeds from the basal to luminal surface of the seminiferous epithelium
Describe spermatogenesis including key processes and names of the cells at different stages
spermatogonium (diploid stem cell) undergoes mitosis providing cell numbers essential for a high sperm output.
While undergoing meiosis they become spermatocytes, and after meiosis, each spermatocyte divides into 4 haploid spermatids.
After that differentiation takes place (morphological changes) and when released spermatids become spermatozoan.
What is the purpose of spermatogonial mitosis? what are the experimental evidence?
Provides lots of cells for meiosis (experimental evidence: PCNA staining marks cells undergoing mitosis in testis)
What are the two paths for spermatogonial stem cells?
They can either self-renew or commit to differentiation.
What are the types of undifferentiated spermatogonia in humans? What is their function?
- Ad (Adark) (renew population)
- Ap (Apale) (provide population for spermatogenesis)
What are the types of differentiating spermatogonia in humans?
B, cannot go back once commited.
What are the types of undifferentiated and differentiating spermatogonia in rodents and chimps?
- In non-human primates similar patterns are seen, they also have Ad and Ap. However, they have more divisions after the spermatogonia entered the differentiation state (B1->B2->B3->B4)
- In rodents (slightly different): Undifferentiated spermatogonia can be Asingle (As), they can self-renew or become Apaired (Apr), continue dividing until they form Aal spermatogonia, form syncytia which are attached together in 4, 8 or 16 cells. Then enter differentiating spermatogonia stage (A1->A2->A3->A4->In->B)
- Key message: undifferentiated spermatogonia keep dividing and can always self-renew, replenish the pool, however when they commit to differentiating spermatogonia, they cannot go back.
What is spermatogonial stem cell niche? What makes it up?
- The spermatogonial stem cell niche is a specialised physical and chemical environment (formed by surrounding cells).
- Made up from: sertoli cells, PTM cells, Leydig cells, blood vessels, lymphatics, differentiated spermatogonia.
- Dividing SSCs can receive signals from all through the testis and through the body, which come from the blood vessels. Physical contact with basement membrane is also essential for signalling
SEE L9, slide 7
What are the ligands that SSCs require for self-renewal?
Paracrine signalling, main ligands FGF2, GDNF, CXCL12, ensures that stem cells still divide
What produces GDNF?
GDNF is produced by peritubular myoid cells
What is a key ligand for spermatogonial differentiation?
Retinoic acid, produced from retinol or vitamin A, that’s why vitamin A essential in our diet
When is retinoic acid released?
Not until after puberty
What is the genomic pathway that retinoic acid acts through?
RA acts on transcription factor, which causes expression (upregulation) of Stra8, promote start of meiosis