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Page 1: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

STEM CELLS

Image Credit: Mesenchymal precursor cells

Page 2: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Division and differentiation All cells reproduce by dividing Cells produced by mitosis are

clones This is how unicellular organisms

reproduce asexually Multicellular organisms are a bit

different When the cells of an embryo

divides, initially they are all the same

Later the cells start to differentiate (specialise)

© 2010 Paul Billiet ODWS

Released into the Public Domain by Jrockley

Image Credit: www.scienceclarified.com

Page 3: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Differentiation and gene expression All the somatic cells (not gametes) of a

multicellular organism contain the same genetic information

But cells in different tissues perform different functions

Cells in different tissues have quite different forms

Therefore, some genes are expressed in a cell and not others

© 2010 Paul Billiet ODWS

Page 4: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Hox genes Genes that control

development are a group called Hox genes

Surprisingly similar for all animals

The sequence in which they express seems to create the differences in development

Image Credit: Hox genes of fruit fly and mouse© 2010 Paul Billiet ODWS

Page 5: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

What causes differentiation? Cells differentiate according to their

position in an embryo Transferring cells from one place to

another illustrates this The signals are called growth factors These factors are released by zones of

cells called organisers The surrounding cells develop along a

determined route

Zebra fish embryology© 2010 Paul Billiet ODWS

Page 6: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Early experiments Displace organiser

cells and the embryo will develop an organ in a different place from usual

Or if a second organiser is added an additional organ will develop

Copyright© 2006 Nature Publishing GroupNature ReviewsMolecular Cell Biology © 2010 Paul Billiet ODWS

Page 7: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Totipotent and pluripotent cells In simple animals (e.g.

sponges) the cells retain their capacity to regenerate into whole new sponge

Totipotent More complex animals

lose this capacity Cells of the early embryo

are capable of turning into any type of cell (pluripotent)

Differentiated cells may not be able to do this

Image Credit: Sea Sponge

© 2010 Paul Billiet ODWS

Page 8: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Stem cells Cells that can develop

into any other cell are called stem cells

A few still exist in the body of an adult

E.g. bone marrow has blood stem cells

E.g. umbilical cords have stem cells

Bone marrow stem cells © David Darling

© 2010 Paul Billiet ODWS

Page 9: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Image Credit: Blood stem cell differentiation

Page 10: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Making stem cells Stem cells could be used to replace tissues

that are damaged or diseased E.g. cardiac muscle will not divide once it

has differentiated Stem cells stimulated to grow into cardiac

cells could replace the need for heart transplants

The problem of tissue typing and tissue rejection still remains

Implanted tissue could become cancerous

© 2010 Paul Billiet ODWS

Page 11: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Cloned stem cells If stem cells can be cloned from the cells

of a patient they can be used to generated genetically identical tissues

Therapeutic cloning Mammalian cells need to be set back to

the beginning of the cell cycle (G0)

© 2010 Paul Billiet ODWS

Page 12: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Somatic cell nuclear transfer SCNT Made famous by Dolly the sheep Oocytes (unfertilised egg cells)

harvested Nuclei removed Somatic cells from animal to be

cloned fused with enucleate oocyte Electric shock sets the cell cycle

to G0

Nuclear genome cloned but… Mitchondrial genome comes from

animal which donated the oocyte

Image Credit: Removing the nucleus from an oocyte

© 2010 Paul Billiet ODWS

Page 13: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

Problems for SCNT in therapeutic cloning Human oocytes are few and difficult to

obtain A lot of oocytes needed to generate

successful cell lines(304 oocytes from 14 macaques to produce 2 cell lines)

Ethical problem of embryo destruction Early embryo cells are harvested to

generate cloned tissues for transplants/grafts

© 2010 Paul Billiet ODWS

Page 14: STEM CELLS Image Credit: Mesenchymal precursor cellsMesenchymal precursor cells

The answers? Fuse somatic cell with

enucleated oocyte of another species of animal

Umbilical cord stem cells

Induced pluripotent stem cells (iPS)(Genetically modified somatic cells reprogrammed back to its undifferentiated state)

Image Credit: Umbilical cord

© 2010 Paul Billiet ODWS


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