somatic, germ and stem cells 1)distinctions between somatic and germ cells. 2)establishment of...

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Somatic, Germ and Stem cells 1) Distinctions between somatic and germ cells. 2) Establishment of somatic cell types. 3) Establishment of the germ line. 4) Fundamental differences in germ cell establishment between organisms. 5) Where stem cells fit in….

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Page 1: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Somatic, Germ and Stem cells

1) Distinctions between somatic and germ cells.

2) Establishment of somatic cell types.

3) Establishment of the germ line.

4) Fundamental differences in germ cell establishment between organisms.

5) Where stem cells fit in….

Page 2: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Cell types

• Two basic classes of cells in animals– somatic cells– germ cells

Somatic cells - almost everything we see and use, skin, muscle, blood, etc.

Germ cells - the cells that are responsible for reproduction, propagation of the species.

Stem cell - neither fish nor fowl. Can in some cases do both.

Page 3: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

1) These two classes of cells are established in different ways during development.

2) There are two fundamentally different processes by which germ cells are generated in different organisms.

Germ vs. Somatic cells

Page 4: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Establishment of somatic cells

Page 5: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Gastrulation generates the three classes of somatic cells

Page 6: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Three classes of somatic cells• Ectoderm (outside)• Endoderm (inside)• Mesoderm (in between)– frequently called the 3 germ layers

Page 7: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Establishment of the germline

• Two different ways in different organisms

1) Preformation (segregation)

2) Epigenesis (recreation)

Extavour and Akam, Development 130:5896 (2003)

Page 8: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Establishment of the germline

• Preformation– Germ cells determinants (germ plasm) are set

aside before or at fertilization and remain segregated throughout the lifespan of the organism.

C. elegansDrosophila

Page 9: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Germline formation in C. elegansIn worms, the point of sperm entry defines the posterior pole of the egg.

a) A fertilized egg with evenly distributed P-granules

b) At pronuclear migration and fusion, P-granules move to the posterior, where the sperm nucleus was located.

c) After first cell division all P-granules in Posterior cell.

d) At 4-cell stage all P-granules are in Posterior P1 cell

Page 10: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Germline formation in C. elegans

6 Founder Cells +98 die

+14 die

+1 dies

Small posterior cell goesgermline

Page 11: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Germline formation in C. elegans

8-cell

24-cell

Antibodies to P-granules

DAPI staining of nuclei

Page 12: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Preformation

• C. elegans, Drosophila and many other model organisms. Some amphibians, birds.

• Segregation of mRNAs and proteins required for germ cell formation and function (germ plasm).– bruno (RNP-type binding protein, regulates translation)– gld-1 (RNA binding protein)– mex-1 (zinc-finger DNA-binding protein)– vasa (DEAD-box RNA helicase, interacts with eIF5b)– germ cell less (transc. repressor, binds E2F)– cycB (B-type cyclin, interacts with CDK1, ubiquitous)– tudor (Tudor domain containing, part of germ granules)

Page 13: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Epigenesis of germline in mammals

• Major distinction, no preexisting germ plasm in oocytes. Primordial germ cells are generated during development.

• Seen in all mammals (so far), many other species.

• Shared feature with Preformation: germ cells are "set aside" before other cell types.

Page 14: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Epigenesis of germline in mouseDevelopmental Cell 2: 537 (2002) Zhao and Garbers, Male Germ Cell Specification and Differentiation

EmbryonicEctoderm

EmbryonicMesoderm

EmbryonicEndoderm

Blue = embryonicwhite = extraembryonic

Page 15: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Epigenesis of germline in mouse

BioEssays 27.2, Matsui and Okamura, Mechanisms of germ-cell specification in mouse embryos. 2005

BMP-4, -8b

BMP receptor

Page 16: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Primordial germ cells• Generated by epiblast.• Separate from the 3 somatic cell layers.• Migrate to gonadal ridge. (Molyneaux et al. Dev. Biol. 240:488 (2001).

• Populate ridge to form germ cells of gonad.

• In vitro, PGCs can differentiate into Embryonal Germ Cells (EGC). (Donovan et al. Cell 44:831 (1986), Matsui et al. Cell 70:841 (1992)).

• This differentiation is similar to the "reprograming" of somatic nuclei seen in Oocytes and ES cells.

• EGCs are one of only a few pluripotent stem cells currently known. Can contribute to all cell types in embryos.

Page 17: Somatic, Germ and Stem cells 1)Distinctions between somatic and germ cells. 2)Establishment of somatic cell types. 3)Establishment of the germ line. 4)Fundamental

Human Embryonal Germ CellsHuman EGCs Mouse ES cells

Cells were grown in DMEM supplemented with 15% fetal bovine serum, 0.1mM nonessential amino acids), 0.1 mM 2-mercaptoethanol, 2 mM glutamine, 1 mM sodium pyruvate, 100 units/ml of penicillin, 100 ug/ml of streptomycin, 1,000 units/ml of human recombinant leukemia inhibitory factor (hrLIF), 1 ng/ml of human recombinant basic fibroblast growth factor (hrbFGF), and 10 mM forskolin.

Shamblott et al. PNAS 95:13726 (1998)