8. Spermatogenesis Flashcards
What are the main phases spermatogenesis?
Spermatogenesis:
Phase 1: proliferation + differentiation (change in numbers)
Phase 2: meiosis (change in genetics)
phase 3: morphological change - tail maturation
Differentiate between different stages of sperm in sermatogenesis
Spermatogenesis states:
- spermatogonium - diploid stem cell
- spermatocyte - after mitotic divisions
- spermatid - after meiosis
- spermatozoan - after fully matured
What are the two possible fates of spermatogonia?
Spermatogonia can:
- continue dividing as stem cells - self-renew the spermatogonia pool
- start differentiating into sperm
Different spermatogonial stages in different species
Describe the spermatogonial stem cell niche
Spermatogonial stem cell (SSC) niche - specialised physical + chemical environment at seminiferous tubule epithelium basement membrane - dividing SCs receive signals from blood + basement membrane -> determine fate - if continue dividing as SCs / start differentiating
What specific signals are required for spermatogonial stem cells to continue dividing?
SSC self-renewal requires paracrine signalling from the SSC niche in seminiferous tubule epithelium basement membrane:
- FGF
- GDNF - produced by peritubular myoid cells - essential for self-renewal
- CXCL12
What is GDNF signal needed for in SSCs?
SSCs need paracrine GDNF signalling for self-renewal - GDNF produced by peritubular myoid cells (PTM) - if GDNF KO -> no sperm stem cells
What signal is required for spermatogonial differentiation initiation?
Retinoic acid (RA) - in males post-pubertally (embryonically in females - in SD) - triggers differentiation of spermatogonia + start of meiosis - RA comes from different cells in SSC niche
Which vitamin is needed for spermatogonial differentiation?
VitA triggers spermatogonial differentiation -> mature sperm
In VitA deficiency (VDA) spermatogonial differentiation can’t be triggerred - no entry to meiosis - no mature sperm
Explain wht is ATRA?
All trans-retinoic acid (ATRA) - signals RA to spermatogonial cells - two pathways:
- genomic pathway - ATRA binds TFs inside the nucleus - affects transcription
- non-genomic pathway - ATRA binds a receptor in cytoplasm - affects a signalling pathway - affects translation
What determines if specific spermatogonium remains a stem cell and keeps dividing or enters differentiation?
The position of the spermatogonium in the niche determines the fate of the stem cell - affects availability of mitogens (chemical/physical) -> determines if differentiates or self-renews
Where are spermatocytes located in the seminiferous tubule?
Spermatocytes - at phase 2 - meiosis - not at basement membrane - moved further - half-way through the epithelium - in between basal-apical
Explain when does the genetic change occur in meiosis
At crossing over of homologous chromosomes - prohase I
How do developing spermatogonia move in seminiferous tubule epithelium from basement to apical membrane?
Physically move by breaking and reforming germ-Sertoli cell attachments - adherens junctions
What is Sertoli-Sertoli barrier important for?
Sertoli-Sertoli tight junction specialised to form blood-testis barrier - protect from immune system - would attack haploid cell
What is essential for spermatogenesis?
Androgens - testosterone - reduction in testosterone causes gradual degeneration of spermatogenesis - no post-emiotic germ cells if no testosterone
What is spermiogenesis?
Spermiogenesis - morphological change of spermatids into spermatozoa
- cytoplasm condensation
- acrosome and tail formation
- DNA compaction
- cytoplasmic storage of mRNAs for future translation
What are the morphological changes in post-meiotic spermatids?
Last step of development - morphological determination - spermiogenesis of spermatozoa - species specific morphology -> in figure mouse / rat spermatozoan morphology
What are the processes involved in spermiogenesis?
Spermiogenesis:
1) Golgi phase
2) Cap phase
3) Acrosomal phase
4) Maturation phase
Explain the difference in DNA packing in somatic cells vs spermatozoa
DNA is more tightly packed in spermatozoa - different proteins used:
- histones -> transition protein 2 -> protamines
When does transcription stop in developing spermatozoa?
Transcription stops in early sermatid nucleus - in spermiogenesis - mRNA storage in cytoplasm for future translation
Explain what is spermiation
Spermiation - release of mature spermatozoa from Sertoli cells into seminiferous tubule lumen - Sertoli-germ cell junctions remodelled - leave behind a residual body - cytoplasm - phagocytosed by Sertoli cell
Why are specific stages of spermatozoan development found to be grouped?
Specific germ cell stages in spermatozoan development are grouped because development is regulated by waves of RA - seminiferous tubules are arranged in groups - segmental / helical arrangement
Why are there different stages of developing spermatozoan germ cells at the same time in one seminiferous tubule epithelium?
Males are constantly fertile - need constant spermatogenesis - several cycles in parallel are happening - one section gets several levels of germ cell development
What is the differences between rodent and human seminiferous tubule arrangement?
Rodent: segmental arrangement
Human: helical arrangement
What controls waves of spermatozoan germ cell development?
Spermatogenic waves are controlled by RA pulses - always occurs at stages VII->VIII at spermiogenesis
Summary of spermatogenesis phases
