Germ Line Development in Vertebrates

Comprehensive flashcards covering germ line development, PGC specification mechanisms (preformation vs. induction), migration pathways, and adult stem cell niches in vertebrates.

What is the primary characteristic of the 'preformation' mechanism of germline differentiation?

Cytoplasmic determinants called germ plasm, already present in the oocyte, specify cells to become germ cells.

What is the primary characteristic of the 'induction' mechanism of germline differentiation?

Germ cells are specified later in development through extracellular signals released from neighboring cells, rather than maternal determinants.

Which two vertebrate species mentioned in the lecture use the preformation mechanism?

Zebrafish and Xenopus

Which two species are examples of the induction mechanism for primordial germ cell specification?

Mouse and human

What is the function of Vasa proteins in germ cell development?

They activate germ-cell-specific genes.

How does the protein Nanos contribute to germ cell development?

It represses translation and prevents cell death.

What is the common role of Tudor and Piwi proteins in germ cells?

They interact and inhibit transcription.

Why is the silencing of transcription and translation critical during primordial germ cell migration?

It prevents germ cells from responding to somatic signals and adopting a somatic cell fate.

In inductive species, which signaling molecules are commonly required to specify germ cells?

BMP signals

What is the Balbiani body?

A dense collection of polar granules, mitochondria, and concentrated germline mRNAs formed during oogenesis.

Which protein acts as the germ plasm organizer in zebrafish?

Bucky ball

What role does miRNA-430 play in zebrafish blastomeres?

It represses Nanos in blastomeres that are destined to become somatic cells.

How do zebrafish germ cells protect Nanos expression from miRNA-430?

The DAZL protein inhibits miRNA-430 within the germ cells.

By the late cleavage stage in zebrafish, approximately how many cells contain germ plasm?

$4$ cells out of approximately $1,000$

In zebrafish PGC migration, which protein is secreted by the target gonad cells?

SDF1

What membrane receptor on zebrafish PGCs binds to the chemoattractant SDF1?

CXCR4

What is the name of the germ plasm organizer protein in Xenopus?

Xvelo

What is the French term used to describe the germline granules (nuage) observed in Xenopus?

\text{Cloud}

At what embryonic stage and day do PGCs typically start to form in mice?

Gastrulation stage, approximately embryonic day $E6.5$

Which three transcription factors are identified as key genes for PGC induction in mice?

Blimp1, Prdm14, and Tfap2c

From where is BMP4 released to initiate PGC specification in the mouse embryo?

Extra-embryonic ectoderm

What is the function of the Anterior Visceral Endoderm (AVE) in mouse germ cell determination?

It produces Nodal and Wnt antagonists to restrict Wnt signaling to the posterior region.

What is the effect of Wnt signaling on posterior cells in the mouse epiblast?

It makes the posterior cells competent to respond to BMP signals.

Which PGC-specific gene is upregulated by Blimp1 in mice?

Stella

Which somatic gene family is repressed by Blimp1 to prevent PGCs from becoming somatic cells?

Hox genes

Describe the migration path of mouse PGCs between days $E8$ and $E9.5$.

They migrate through the hindgut into the mesoderm.

At what embryonic days do mouse PGCs undergo bilateral migration to the genital ridges?

$E10.5$ to $E11.5$

Which receptor and ligand pair regulates the speed of PGC migration in mice?

The c-kit receptor tyrosine kinase (RTK) and its ligand, Steel.

Which adhesion molecule is required for mouse PGCs to migrate out of the hindgut?

$\beta 1$ integrin

What adhesion molecule is specifically mentioned as important for mouse PGC entry into the gonad?

E-cadherin

What protein is secreted by cells in the 'traveling niche' to promote PGC survival and division in mice?

Stem Cell Factor (SCF)

What term is used for committed germ cells in the gonads after they lose pluripotency?

Gonocytes

At approximately what Carnegie stage (CS) are human PGCs specified?

$$\text{CS6}$$

Which tissues in the human embryo secrete Wnt3A to drive PGC specification?

Cytotrophoblast and epiblast

Which two transcription factors are markers of PGC specification in humans?

SOX17 and TFAP2\gamma (SOX-box transcription factor 17 and transcription factor AP-2\gamma)

What two signaling pathways active EOMES in human PGC development?

Wnt and Nodal signaling

In human PGC development, which protein is activated by BMP4 to then help activate SOX17?

GATA3

Name one major difference between human and mouse PGC specification regarding BMP signaling.

In humans, BMP signaling downregulates SOX2, whereas it does not in mice.

Which transcription factor is required for human PGC specification but not for mouse PGCs?

SOX17

At Carnegie stage 10 ($\text{CS10}$), where are human PGCs located?

Near the allantois in the yolk sac endoderm.

How do human PGCs move into the body of the embryo during $CS11$ onwards?

They are passively incorporated into the ventral wall of the hindgut epithelium as the embryo folds.

By week $6$ ($CS17$), what do human PGCs differentiate into in male and female embryos?

Mitotic pro-spermatogonia (gonocytes) in males and oogonia in females.

Where are spermatogonial stem cells (SSCs) located in the adult male?

Seminiferous tubules in the testes.

How were SSCs initially defined in mice?

Through transplantation assays where donor cells regenerated colonies of spermatogenesis in a recipient testis.

Why is the SSC niche described as an 'open' niche?

Niche factors are randomly distributed between SSCs, primed cells, and committed progenitor cells.

Which substance, released from Sertoli cells and macrophages, promotes SSC differentiation?

Retinoic acid

What percentage of cells in the testis are spermatogonial stem cells (SSCs)?

$$0.02\%-0.03\%$$

What is a potential medical risk associated with the aging of SSCs in men?

An increase in de novo mutations associated with congenital disorders.

When were Female Germline Stem Cells (FGSCs) identified in mammalian ovaries?

In $2004$

What long-standing theory was challenged by the discovery of FGSCs?

The theory that females have a finite supply of oocytes that stops at birth.

Name two common markers used to identify both PGCs and FGSCs.

OCT4 and DAZL

How does estrogen stimulation regulate FGSC activity?

It upregulates Stra8 expression, which triggers oocyte development.

What are the two potential gamete outcomes of FGSCs maintaining homeostasis?

They differentiate into primary oocytes and mature follicles to replenish the follicular pool.

Which enzyme complex is responsible for removing epigenetic signatures from the gonocyte genome?

Epigenetic signatures are removed so that male or female marks can be superimposed (exact enzyme name not listed, attributed to enzyme complexes).

List one future application of FGSC research for female healthcare.

Fertility preservation or delaying menopause.

What is 'spermiogenesis'?

The process of generating haploid spermatozoa from spermatids.

What stage of oocyte development is reached upon ovulation just before fertilization?

Meiotic metaphase II (MII)

What is the role of Dazl in the mouse genital ridge?

It is an RNA-binding protein that blocks pluripotency networks to allow PGCs to become committed germ cells.

Which adhesion molecule is crucial for PGC entry into the gonad?

E-cadherin

What experiment in $2023$ by Murakami et al. demonstrated a major breakthrough in germ cell research?

The generation of functional oocytes from male mice in vitro.

In the zebrafish embryo, where does Bucky ball lead the germ plasm components after fertilization?

To the cleavage furrows.

What is the function of PRDM14 and SOX15 in human PGCs?

They are important for PGC maintenance.

Name the two tissues that secrete BMP2 and BMP4 to drive human PGC specification.

Extra-embryonic mesenchyme and the amnion.

Describe the morphology of PGCs at day $E7.5$ in mice.

Smooth and round morphology.

Which protein prevents cell death in germ cells during migration?

Nanos

What is the primary marker used to track PGC migration in zebrafish studies?

Vasa

What role does the protein PIE-1 play in C. elegans germ line development?

It regulates germ line gene expression.

In humans, where does the first expression of SOX17 and TFAP2\gamma occur at day $E11$?

The dorsal amnion.

What molecules form the 'dense disk' at the vegetal cortex during Zebrafish stage III-IV oogenesis?

Germinal granules and germ plasm RNAs.

Which signaling protein is described as dispensable for human PGC specification despite activation by Wnt?

TBXT