In cell nucleus, polar and neutral lipids are responsible for the nuclear membrane and nuclear matrix fluidity. In specific sections of inner nuclear membranes that bind the active chromatin, lipid microdomains that constitute a platform for the transcription process are present.
Nuclear lipid microdomains appear as a homogenous population of closed, spherical or ovoid vesicle-like structures composed by an exact ratio of phosphatidylcholine, sphingomyelin and cholesterol. This ratio is maintained by neutral sphingomyelinase, sphingomyelin-synthase and reverse sphingomyelin-synthase activity. Interestingly, exist two pools of cholesterol in the chromatin: one called "sphingomyelin-free cholesterol fraction" and another "sphingomyelin-linked cholesterol fraction". The latest fraction is regulated by neutral sphingomyelinase and sphingomyelin-synthase activity. The organization of sphingomyelin-linked cholesterol fraction in chromatin microdomains is reported in this commentary.