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….
17
Embed
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.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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….
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.
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
Establishment of somatic cells
Gastrulation generates the three classes of somatic cells
Three classes of somatic cells• Ectoderm (outside)• Endoderm (inside)• Mesoderm (in between)– frequently called the 3 germ layers
Establishment of the germline
• Two different ways in different organisms
1) Preformation (segregation)
2) Epigenesis (recreation)
Extavour and Akam, Development 130:5896 (2003)
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
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
Germline formation in C. elegans
6 Founder Cells +98 die
+14 die
+1 dies
Small posterior cell goesgermline
Germline formation in C. elegans
8-cell
24-cell
Antibodies to P-granules
DAPI staining of nuclei
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)
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.
Epigenesis of germline in mouseDevelopmental Cell 2: 537 (2002) Zhao and Garbers, Male Germ Cell Specification and Differentiation
EmbryonicEctoderm
EmbryonicMesoderm
EmbryonicEndoderm
Blue = embryonicwhite = extraembryonic
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
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.
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.