4. Gametogenesis Flashcards
(21 cards)
What are somatic cells?
Cells of the body that support and protect germ cells
They are genetically a dead end as their DNA is not transmitted to the next generation.
What is the primary role of germ cells?
To form gametes (sperm or eggs) and transmit DNA to future generations
Germ cells are considered the most important cells from an evolutionary perspective.
What are the two major mechanisms of germ cell specification?
- Predetermined (Autonomous) Specification
- Inductive Specification
Describe Predetermined (Autonomous) Specification.
Germ cells are specified very early in development through maternal determinants concentrated in a specific region of egg cytoplasm
Found in nematodes, insects, fish, and frogs.
Describe Inductive Specification.
Germ cells develop later through signaling from neighboring cells after implantation and gastrulation begins
Found in mammals, including humans.
True or False: In mammals, germ cells are predetermined in the early embryo.
False
Human twinning and IVF observations indicate that germ cells can form anew.
Name a conserved molecular marker of germ cells.
- Vasa
- Nanos
- Tudor proteins
- PIWI
What is the function of Vasa?
An RNA-binding protein that increases translation of germ cell-specific genes
What is the role of Nanos?
An RNA-binding protein that represses translation of somatic genes and prevents apoptosis during migration
What initiates mammalian germ cell development?
Begins after gastrulation, around day 13 in humans, day 6 in mice
Gastrulation involves differentiation into three primary germ layers.
What are primordial germ cells (PGCs)?
Cells that remain pluripotent and do not enter differentiation pathways during gastrulation
What induces epiblast cells to become PGCs?
Bone Morphogenetic Proteins (BMPs)
BMPs activate specific transcription factors and germ cell markers.
What happens if BMP-producing cells are destroyed?
Neighboring cells can replace them and still induce PGCs
Where do PGCs migrate from and to?
From the yolk sac to the genital ridge (future gonad site)
What factors are involved in PGC migration?
- Nanos and Dead End proteins
- Kit ligand
- Specific extracellular matrix proteins
At what stage are male and female gonads indistinguishable in humans?
At approximately 6 weeks of development
What drives male development in humans?
The presence of the Y chromosome, specifically the SRY gene
What is the role of the SRY gene?
It is a transcription factor that triggers male development
Brief expression is sufficient to induce this development.
What controls the fate of PGCs?
The genital ridge environment, not the PGCs themselves
What can improper PGC migration lead to?
- Infertility
- Teratomas
What is a potential consequence of mutations in the SRY gene?
Sex reversal syndromes
