Some Unsolved Problems About Cell Differentiation: November 16, 2018

"Cytodifferentiation" = Differentiation. Examples: becoming a liver cell, cardiac muscle cell, macrophage, B-lymphocyte, T-lymphocyte, Granulocyte, Rod cell, Cone cell, Oligodendrocyte, Schwann cell, etc.
More than a hundred differentiated cell types in humans and other mammals 
(Somewhat arbitrary which consider different: Red sensitive cone cells, vs green vs blue sensitive)

"Stem cells" which used to be called "Archeocytes" are undifferentiated and/or able to become any of several differentiated cell types (maybe any or all differentiated cell types). )

"Luxury genes" (only in differentiated cells) as compared with "Housekeeping genes" (in all cell types) )

Being differentiated is usually self-perpetuating (seldom reversible) . Plant cell differentiation is more changeable. )

The mechanism of self-perpetuation is not yet known. You might become the researcher who discovers how it works. )

If you fuse a mouse liver cell with a chicken liver cell, the "heterokaryon" will continue to transcribe the liver luxury genes for both species. But if you fuse either a mouse or a chicken liver cell with either a mouse or chick heart muscle cell, then both sets of luxury genes "will be turned off" (will stop transcription);
as if both differentiated states turned each other off. )

Thought question: Imagine discovering a method that caused anti-myelin multiple sclerosis cells to fuse with any other differentiated cell type. Or maybe that causes anti-myelin B cells to fuse with anti-myelin T lymphocytes. )

Two exceptions to this rule about "turning off" each other's luxury genes: )

Bird red blood cells have nuclei, but these are very shrunken and don't transcribe. Fusing a chicken red blood cell with a mouse heart muscle cell will result in the chicken nucleus swelling and transcribing bird heart muscle genes and making heart muscle proteins. How could you explain this? Does it tell you anything about mechanisms that control gene expression? )

Fusing chicken liver cells with (multinucleate) skeletal muscle cells will result in the liver cells switching cell types, and transcribing chicken voluntary muscle cells. Please suggest a molecular explanation. )

Suppose all the luxury genes of each differentiated cell type had promoter regions with the same base sequence. Why might you expect that? As the basis for controlling differentiation? How could such a pattern be detected? )