stem cells

what is a stem cell?

a relatively undifferentiated cell that produces two things when it divides:

1. one cell that retains the undifferentiated state

2. one cell that can undergo one or more paths of differentiation

where are stem cells found in the body?

gut, epidermis, bone marrow (all places where stem cells regularly divide to replace worn-out cells)

prostate, heart (stem cells divide only under special physiological conditions)

embryonic stem cells

derived from inner cell mass of mammalian blastocysts or from fetal gamete progenitor (germ) cells » these can form any cell

adult stem cells

found in the tissues of the organs after organ maturation » can only form a subset of cell types

totipotency

can generate every cell in embryo and the trophoblast

pluripotent

can generate all cells of embryo except trophoblast

multipotency

limited

unipotency

only make one cell type (spermatogonia)

committed stem cells

are both multipoint and unipotent

progenitor cells are

not capable of unlimited self-renewal; can divide only a few times before differentiating

usually more differentiated than stem cells and have become committed to becoming a particular type of cell

what are the different types of adult stem cells?

• epidermal stem cells

• neural stem cells

• hair stem cells

• melanocyte stem cells

• muscle stem cells

• tooth stem cells

• gut stem cells

• germline stem cells

what are some characteristics of adult stem cells?

• difficult to isolate, fewer than 1/1000 cells

• low proliferation rate

despite the negative characteristics of adult stem cells…

• one mammary stem cell » an entire mammary gland

• neural stem cells from midbrain of adult rats cultured with paracrine factors differentiate into dopaminergic neurons that can ameliorate rodent parkinson’s

too much stem cell differentiation leads to…

depletes the stem cells, promotes aging or decay, “grays” the hair, cancer

too little stem cell differentiation leads to…

cancer

mesenchymal stem cells

bone-marrow-derived stem cells; multipotent

• can be found in fat, muscle, thymus, dental pulp, umbilical cord

• can give rise to bone, cartilage, muscle, and fat