Zaidi: Specialized Tissues, Stem Cells and Tissue Renewal Flashcards
Characteristics of stem cells
Not terminally differentiated Can divide without limit Can renew themselves Can divide into stem cell or differentiate into different cell type Undergo slow division
Totipotent
Give rise to all cells of organism- Zygote
Pluripotent
Give rise to all cells of embryo and adult tissues- Embryonic stem cells
Multipotency
Give rise to different cell types of a given lineage- Adult stem cells
Asymmetric division
Stem cell divides into one stem cell and one with ability to differentiate
Independent choice
Stem cell division makes 2 identical cells but the outcome is stochastic and/or influenced by the environment
Drawbacks of asymmetric division
Cannot explain how existing stem cells rapidly increase their numbers
Flexibility of independent choice
Explains the sharp increase in stem cell numbers when needed for repair
What happens if an adult organ needs to be renewed
Founder stem cells can divide, giving rise to one daughter cell that remains a stem cell and a set of cells that have a set number of transit amplifying divisions
What determines founder cells during development
Short range signals
Transit amplifying cells
Cells that divide frequently - Transit from a cell with stem cell characteristics to a differentiated cell
Programmed to divide a limited number of times
Granular cells
Cell layer underneath prickle cells that form waterproof barrier between inner metabolically active strata and outer dead epidermis cells
Outermost layer of skin
Squame- flattened dead cells densely packed with keratin
Cell layer above basal cell layer
Prickle cells-several layers
The only dividing cells in the epidermis are
Basal cell layer
When basal cells move to layers above to renew, there is a change in
Change in gene expression at each step of differentiation
Time from birth of basal cell to shedding is
One month
What controls number of stem cells in basal layer
Contact with basal lamina
Maintenance of contact preserves stem cell potential, loss of contact triggers terminal differentiation
Proliferative potential of stem cells is directly correlated to
Expression of B1 subunit of integrin (helps mediate adhesion to basal lamina)
Clusters of cells with high levels of integrin found near basal lamina
Factors governing renewal of epidermis
Rate of stem cell division
The probability that one of the daughter cells remains a stem cell
Rate of division of transit amplifying cells
Timing of exit from basal layer and the time the cell takes to differentiate and be sloughed away from surface
What is the most important signal for basal stem cells
Contact with basal lamina- mediated via integrin signaling
Loss of contact abolishes stem cell characteristics and promotes formation of cells that differentiate
Overactivation of hedgehog pathway
Cells continue to divide after exit from basal layer
Deficit of hedgehog signal
Loss of sebaceous glands
Up regulation of Wnt signaling
Causes extra hair follicles to develop
Loss of Wnt signaling
Leads to failure of hair follicle development
Notch signaling
Restricts size of stem cell population
Lateral inhibition causes
Neighbors of stem cells to become transit amplifying cells
TGFb plays key role in
Repair of skin wounds, promoting formation of collagen rich scar tissue
