Caption: Differentiating stem cell (CD34+) from umbilical cord blood. Shown here is the first stage of a CD34+ stem cell differentiating in to another blood cell type. Note the new protoplasmic bulge forming at one position on the CD34+ stem cell periphery; this new growth extension of the cell is the first morphological sign of the stem cell developing in to another cell type. CD34+ stem cells are normally found in the umbilical cord and bone marrow as hematopoietic stem cells. CD34+ stem cells are multipotent because they differentiate to produce precursor (progenitor) cells of any of the body's blood cell types. This process of stem cell differentiation in the circulatory system is called hemopoiesis. Hematopoietic stem cells develop either into red blood cells, or one of several types of white blood cells that make up the immune system. Blood cells have short life spans and are therefore constantly produced by the bone marrow. There are three main types of mammalian stem cells: embryonic stem cells, derived from blastocysts; adult stem cells, which are found in some adult tissues; and cord blood stem cells, which are found in the umbilical cord. The purification and isolation of stem cells from umbilical cord blood allows scientists to research the function of the immune system and to develop treatments for diseases such as AIDS, leukemia and other immune diseases. CD34 is a cluster differentiation molecule present on undifferentiated stem cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. As these cells begin to develop as distinct cell lineages the cell surface markers are no longer identified.
Magnification*: x2,600
Type: SEM
Copyright 2008 Dennis Kunkel Microscopy, Inc.
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