One very intriguing development reads that the "skeletal" stem cells seem to to provide a "niche" or home for the other type of stem cell, the hematopoietic (blood) stem cells. This is a better term, because all the cell types that these cells can generate are indeed found in the tissues that together make the skeleton (bone, cartilage, fat in the bone marrow cavity of the bones). Both types of studies have converged in identifying the non-hematopoietic (blood) stem cells in the bone marrow (widely called "mesenchymal" stem cells) as "skeletal" stem cells. Interestingly, studies in humans have for once paved the way to similar studies in the mouse. Significant advances have now been made in this direction. The challenge is to identify and pick out the cells that can both self-renew (produce more of themselves) and can differentiate into three cell types – bone, cartilage and fat. Some of the cells in the mixture may be able to form bone or fat tissues, for example, but still do not have all the properties of mesenchymal stem cells. But isolating the tiny fraction of cells that are mesenchymal stem cells is more complicated. It is fairly easy to obtain a mixture of different mesenchymal cell types from adult bone marrow for research. Only about 0.001-0.01% of the cells in the bone marrow are MSCs. Among them are blood stem cells(also called hematopoietic stem cells HSCs) and a variety of different types of cells belonging to a group called ‘mesenchymal’ cells. The bone marrow contains many different types of cells. It has not yet been established whether the cells taken from these other tissues are really the same as, or similar to, the mesenchymal stem cells of the bone marrow. There have since been many claims that they also exist in a wide variety of other tissues, such as umbilical cord blood, adipose (fat) tissue and muscle. MSCs were originally found in the bone marrow. They have not been proven to make other types of cells of the body. Mesenchymal stem cell differentiation: MSCs can make fat, cartilage and bone cells. In other cases, the results were an artificial effect caused by chemicals used to grow the cells in the lab. In some cases, it appears that the MSCs might have fused together with existing specialized cells, leading to false conclusions about the ability of MSCs to produce certain cell types. These results were not confirmed in later studies. Some early research suggested that MSCs might also differentiate into many different types of cells that do not belong to the skeletal tissues, such as nerve cells, heart muscle cells, liver cells and endothelial cells, which form the inner layer of blood vessels. These specialized cells each have their own characteristic shapes, structures and functions, and each belongs in a particular tissue. For example, they can differentiate − or specialize − into cartilage cells (chondrocytes), bone cells (osteoblasts) and fat cells (adipocytes). MSCs make the different specialized cells found in the skeletal tissues. They are ‘multipotent’, meaning they can produce more than one type of specialized cell of the body, but not all types. MSCs (also known as Mesenchymal Stem Cells, Mesenchymal Stromal Cells or Medicinal Signalling Cells) are an example of tissue or 'adult' stem cells.
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