Lecture 6- Exam Flashcards
What are stem cells? and what arises from them?
Cell that is not yet specialized - all cells in body come from them - 200 different kinds of specialized cells
What is the process of specialization called?
Differentiation
What makes stem cells special?
They can self-renew to make more of themselves and they differentiate into specialized cells
What is pluripotent? What is an example?
Stem cells that can become many types of cells in the body like embryonic stem cells
What is multipotent? What is an example?
Stem cells that can become only a few types of cells, an example is tissue stem cells in organs
What makes stem cells valuable? (applications)
They can be used for cell therapy to transplant specific cells and precursors to fix cell defects, they can be used for research in vitro and in vivo to understand genes, proteins, and tissue growth and development, and can be used to generate new drugs - efficacy and toxicity screening can be tested on differentiated stem cells
What are tissue stem cells? and what is their purpose?
Adult stem cells that reside in most tissue of the body where they are involved in repair and replacement during apoptosis
What makes up a blastocyst? and around when does it form?
Inner cell mass with 10-15 cell aggregate and a tropechtoderm outer layer - day 6
Which stem cells are difficult to isolate?
Tissue stem cells
What determines the fate of cells inside an early embryo (pre-blastocyst - 4 cell embryos)?
The location of cell inside the embryo - cells on the outside tend to become the trophectoderm and those in the center tend to become the inner cell mass
What are researchers trying to determine for embryonic stem cell cultures?
Appropriate culture conditions that keep cells from differentiating
What genes/proteins regulate pluripotency of ES cells?
Oct4, Sox2, Nanog - activate genes for self-renewal, pluripotency to maintain stemness, and repress genes that induce differentiation pathways
What is the lineage of cells?
In symmetric division cells self renew and then can undergo asymmetric division to produce differentiation of cells, other wise they just continue to generate daughter cells that are identical and will eventually die off - balance leans toward asymmetry
How was stem cell lineage tracked?
In c. elegans (nematode worm) where every cell type was tracked to predict division and direction - demonstrated localization of symmetry versus asymmetry
What is the stem cell niches in drosophila?
Germ-line stem cells - maintained by cap cell signaling to germ line stem cells by hedgehog, somatic stem cells - maintained by inner sheath cell signaling with hedgehog which maintains stemness
What is a stem cell niche?
It is the elements that protect the stemness - do not allow for differentiation - specific cells secrete soluble factors that signal to stem cells to not differentiate
What is the stem cell niche in C. elegans?
Distal tip cells signal to the germ-line cells to maintain stemness
What is happening in intestinal stem cells?
Intestinal stem cells are repopulating up the villi as they pass a proliferation zone and then a differentiation zone and undergo apoptosis at the tip, paneth cells maintain villi by secretion and signalling
How can intestinal stem cells regeneration be visualized?
Using pulse-chase experiments where there is radiolabeling of stem cells in the base of the villi and over a few days looking at their migration which you can see move updward
What are the stem cells at the base of intestinal crypts and what is this pathway/how was it determined?
Lgr5+ - a promoter that signals to cre gene bound to estrogen receptor - cre-ER binds tamoxifen and moves to nucleus where it interacts with two loxP sites and removing the blocking segment in beta-galactosidase - determined by mating two strains of mice and using pulse-chase lineage tracing
What contributes to cell polarity and asymmetrical division?
Aggregation of localized determinants
Which proteins are asymmetrically localized in worm embryos? And what do mutations in these proteins cause?
Par proteins - partition, mutations cause a loss of asymmetry that will cause cells to not become specialized
How is asymmetry induced in the worm embryo?
Unfertilized embryos have evenly distributed acto-myosin networks and uniform Rho-GEF background, but after fertilization there is a loss of Rho-GEF pathway which induces a loss of the myosin network which pushes everything to the left creating asymmetry on the opposite site of sperm entry - creates a gradient of Rho-GEF signaling - cytoskeleton remodeling
What are the two ways stem cells can be induced to divide asymmetrically?
Local determinant aggregates or stem cell niche
What happens in normal adult liver stem cells versus injured?
In normal conditions the hepatocytes divide and repopulate to maintain themselves, whereas in injury they are doing regeneration and differentiation to produce liver progenitor cells (LPCs)
Where is Sox2 expressed?
Pluripotent cells, fetal progenitors, adult progenitors and stem cells
What gives Sox2 specificity to maintain stemness?
It antagonizes other differentiation transcription factors from specific tissues
How do Sox factors act as inducers of cellular reprogramming?
They interact with other transcription factors in certain cell types to induce different cell types
How does Sox2 control self-renewal and differentiation in different types of stem cells?
Sox2 is part of a coregulatory complex that has different components in different cell types - complex binds to DNA regulatory regions - activates genes needed for self renewal, while interacting with other proteins that inhibit cell differentiation - can also interact with histone methylation modifications that activate or inhibit
What happens to stem cells as we age?
We lose some of the population due to damage to biological macromolecules - mutagens can effect genomic DNA and mitochondria, proliferation can effect telomeres and genomic DNA, ROS can effect everything, etc which leads to apoptosis, senescence, altered physiology, etc - need stem cells to fix these errors
What is the clinical translation of stem cell use?
Donated embryonic stem cells can be differentiated in vitro and directly transplanted into patient and monitored by imaging
What are some barriers in the clinical translation of stem cells?
Do cells maintain their viability, will they engraft correctly, will they differentiate and mature as they should within the body and integrate into the proper tissue, do they induce immunogenicity or tumorigenicity?
What are the steps of stem cell therapy?
Stem cells isolated and purified -> matured and differentiated -> gives mixture of cells -> sort for tart cells and combine with imaging probe -> label cells and transplant by intravenous delivery or intraoperative delivery -> perform serial imaging to monitor for safety and efficacy
