Lecture 2

Front 1

How does a somatic cell become a primordial germ cell(PGC)?
epiblast and extraembryonic ectoderm

Back 1

Precursor cells of PGCs are induced within the proximal rim of the epiblast (the epiblast will become the embryo) by the functions of BMP (bone morphogenetic protein) signals provided from adjacent extraembryonic ectoderm. The extraembryonic extoderm is not the embryo this tissue will become the placenta.

Front 2

How does a somatic cell become a primordial germ cell(PGC)?
Bone morphogenetic proteins (BMPs).

Back 2

members of the transforming growth factor type beta superfamily of growth that function as homodimers or heterodimers to signal through heteromeric receptor complexes and downstream SMAD proteins.

Front 3

How does a somatic cell become a primordial germ cell(PGC)?
Blimp 1 expression and Lin28 expression.

Back 3

Bone morphogenic proteins (BMP) acting through Smads result in Blimp 1 expression. Blimp 1 is a master regulator of PGC specification. Lin28 is necessary in PGC specification, Lin28 expression results in decreased let7 mRNA. Let7 miRNA targets Blimp1 mRNA. Therefore, Lin28 allows Blimp 1 to be expressed.

Front 4

How does a somatic cell become a primordial germ cell(PGC)?
Role of E-cadherin

Back 4

Expression of the cell adhesion molecule E-cadherin allows cells to come together and to communicate to form PGCs. Cell-cell interaction is important during the specification of PGCs, which are mediated by these cell adhesion molecules.

Front 5

How does a somatic cell become a primordial germ cell(PGC)?
Hox genes

Back 5

Hox genes go up in the somatic cell neighbors and down in pluripotent germ cells.

Front 6

How does a somatic cell become a primordial germ cell(PGC)?
Essential feature of PGC specification.

Back 6

Turning off genes that initiate somatic cell fate - Evx1, Hox genes, and brachyury and maintenance (or switching on) of genes that maintain pluripotency in the germ cell lineage, including Stella, fragilis (Ifitm3), Oct4, Sox2, Nanos3 and Nanog.
Research has shown AP-2gamma is also necessary for PGC specification.

Front 7

PGC (primordial germ cell) migration (where does it start and end)

Back 7

PGCs originates in the proximal epiblast, they must migrate through the hindgut to get to the genital ridge and populate the gonad. Proliferation occurs as the PGCs migrate. A Kit ligand gradient attracts PGCs to the genital ridge and incudes apoptosis if get off track. This is important to prevent germ cells tumors. Kit Ligand, E-cadherin.

Front 8

Meiosis vs Mitosis

Back 8

Only occurs in Germ Cells. Gives rise to male and female gametes. Mitosis results in the formation of two identical daughter cells. There is no exchange of genetic material occurs between homologous chromosomes, so sister chromatids (i.e. two copies of the same DNA on a chromosome) are identical. A second reason for genetic identity is that the sister chromatids of each chromosome split, one going to each daughter cell druing anaphase of the single mitotic dvision.
There are to meiotic divisions which result in haploid cells.

Front 9

importance of meiosis

Back 9

important for shuffling of alleles (genetic traites)
1. homologous recombination
2. independent assortment of chromosomes

Front 10

major difference between male and femal gametogenesis

Back 10

One spermatogonium yields four spermatids whereas one oogonium yields one mature oocyte and two polar bodies.

Front 11

How do PGCs know how to find the gonad?

Back 11

Kit ligand is released from the gonad and acts as an attractant - forms a gradient and guides PGCs to the genital ridge.
Kit receptor on the PGCs.

Front 12

When do male and female germ cells enter meiosis?

Back 12

Germ cells enter meiosis at puberty in the testis. Germ cells enter meiosis in the fetus (ovary).

Front 13

What initiates the entry of germ cells into meiosis?

Back 13

Retinoic acid released from the mesonephros.