LIFESCI 2A03 Lecture Notes - Lecture 5: Adult Stem Cell, Asymmetric Cell Division, Progenitor Cell

132 views10 pages
LECTURE 5 LIFESCI 2A03
1
Lecture 5: Stem Cell Niche
October 1, 2013
Preformationist theory of development semen contains an embryo, a preformed miniature infant, or homunculus, that
becomes larger during development
o View persisted into the 18th century
o Problems
Genetics from both parents not possible
No evidence (microscopy at the time not sufficient)
Sperm is single cell; suggests many tiny cells within sperm forming homunculus
Generational problem inside homunculus there are millions of sperm cells with homunculus, inside whith
there are millions of sperm etc too microscopic
Other theory was that animal emerges gradually from a relatively formless egg
During the 19th century, improvements in microscopy allowed biologists to see that embryos took shape in a series of
progressive steps after the fusion of egg and sperm (germline cells)
Adult Stem Cells
Adult Stem ells cells that can divide to create two cells; another stem cell or a cell more
differentiate than itself
o Cells:
A (purple) = stem cell
B (blue) = progenitor cell
Terms stem cell and progenitor cell are often used interchangeably;
stem cell pluripotent; progenitor cell more differentiated (multipotent,
unipotent)
C (yellow) = differentiated or specialized cell
o Processes
1 = symmetric cell division
2 = asymmetric cell division
3 = progenitor division
4 = differentiation
Symmetric Cell Division two identical daughter cells are created (both stem cells)
Asymmetric Cell Division the two daughter cells are different from one another (one stem cell and a progenitor cell with
limited self-renewal potential or a differentiated cell)
o Maintains homeostasis of a system that tends to maintain a stable, constant condition
o One stem cell and one differentiating cell maintains a balance between stem cells and undifferentiated cells
o Difference between two cells after asymmetric division
1. Differential segregation of
mRNAs
cystolic proteins
cell membrane proteins
2. Differences in surrounding environments
o Two mechanism of asymmetric cell division
A. Extrinsic fate determinants = the daughter cells are placed in different microenvironments
One cell stays in stem cell niche (maintains contacts and signals with niche); one cell pushed out
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 10 pages and 3 million more documents.

Already have an account? Log in
LECTURE 5 LIFESCI 2A03
2
B. Intrinsic fate determinants = asymmetric localization of components within the dividing cell that results in
their differential segregation
Cell begin asymmetric; one cell has determinants, other does not
Stem Cell Niche microenvironment that maintains stem cell identity
o The niche has been studied in greatest detail for the germ line stem cells, but niches are being defined for many
somatic adult stem cells
Adult stem cells fall into two categories
o Somatic stem cells (that we have been discussing) different somatic stem cell lineages go on to create or replenish
body cells
o Adult stem cells create germ line cells (sperm and eggs)
Eg/ half the body of a female fruit fly is for developing eggs
Drosophila ovaries model system for studying the stem cell niche
o Ovaries divides into ovariole (string of maturing eggs; bottom mature egg, follicles along ovariole are developing eggs)
o Far right = ovaduct
o Drosophila ovaries contain germ line cells that will go on to form the egg and somatic cells that support egg
development
o We will focus on the anterior end of the ovariole where the germ line stem cells reside in their niche
o Developmental life span (egg to adult) = 12 days
o Grow and breed quickly; do not require a lot of maintenance; cheap medium to grow them on
o Protein coding sequences are similar between drosophila and humans can identify important gene in humans and
observe what happens in drosophila
Germ Line Stem Cells (GSCs) undergo asymmetric cell division’
o One cell retains stem cell identity, one cell (cystoblast, CB) eventually becomes the egg
o Cyst group of germ line cells that result from mitotic division of the cystoblast one of the
cells will become the egg, other cells become supporting cells
Drosophila ovary or germarium
o Stem Cell Niche (red) terminal filament, cap and inner sheath cells express molecules important for the maintenance
and self-renewal of female GSCs
o GSCs (light green) undergo asymmetric cell division, giving rise to one daughter cell that will retain stem cell identity
and one daughter cell, a cystoblast (CB), which will initiate differentiation (dark green)
While the germ line cells go on to form the egg, somatic cells form the niche
To identify the germ line cells, use a cellular marker
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 10 pages and 3 million more documents.

Already have an account? Log in
LECTURE 5 LIFESCI 2A03
3
o The fusome (or spectrosome) is found only in germ line cells use antibody to proteins within this structure to
identify the germline cells
o Germ cells identified to follow through development;
green stains the fusome of germline cells
o Germline cells:
GSCs germline stem cells (red); red when
toching niche
CB cystoblast; no longer red when out of niche
CS - cysts
o Somatic Cells of the Niche (blue)
TF terminal filament
TGS inner sheath cells
Cpc cap cells
o Germline markers (green)
FS fusome; grows as cystoblast divides
SS spectrosome; in cells at end of germarium touching niche
o Two or three GSCs are located at the tip of the ovariole (germarium) and are surrounded by the niche which is made
up of: terminal filament cells, cap cells and inner sheath cells
GSCs undergo asymmetric cell division
o GSC stays in the niche and retains stem cell identity
o Cystoblast (CB) leaves the niche; undergoes mitotic divisions to form the cyst (in which, one cell will become the egg)
The GSC and the cystoblast differ in the intrinsic factors and extrinsic factors that determine their identity
o Intrinsic Factors
Cyst oblasts require the expression of two genes
Bag of marbles (bam) and benign gonial cell neoplasm (bgcn) code for products expressed in
germline stem cell
While germline stem cells express a different set of intrinsic factors to maintain their identity
o Extrinsic Factors
Germline stem cell niche
Germline Stem Cell Niche
o Papers regarding the GSC niche in Drosophila ovary trying to identify signaling roles in stem cell niche
Song et al. 2003. Bmp signals from niche cells directly repress transcription of a differentiation-promoting
gene, bag of marbles, in germline stem cells in the Drosophila ovary. Development. 131: 1353-1364.
Chen, D. and D. McKearin. 2003. Dpp signalling silences bam transcription directly to establish assymetirc
divisions of germline stem cells. Current Biology. 13(20): 1786-1791.
Review Article looks at the whole field; not in depth
Primary Article
o Germline stem cell niche in Drosophila ovary
o Different between stem cells and differentiated cells
GSC needs to remain undifferentiated, needs to undergo cell division (self-renewal of stem cells)
CB needs to differentiate
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 10 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Preformationist theory of development semen contains an embryo, a preformed miniature infant, or homunculus, that becomes larger during development: view persisted into the 18th century, problems. No evidence (microscopy at the time not sufficient) Generational problem inside homunculus there are millions of sperm cells with homunculus, inside whith. Sperm is single cell; suggests many tiny cells within sperm forming homunculus there are millions of sperm etc too microscopic. Other theory was that animal emerges gradually from a relatively formless egg. During the 19th century, improvements in microscopy allowed biologists to see that embryos took shape in a series of progressive steps after the fusion of egg and sperm (germline cells) Adult stem ells cells that can divide to create two cells; another stem cell or a cell more differentiate than itself: cells: Terms stem cell and progenitor cell are often used interchangeably; stem cell pluripotent; progenitor cell more differentiated (multipotent, unipotent) C (yellow) = differentiated or specialized cell: processes.

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
Booster Classes
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
Booster Classes