Repair in the developing heart( If the heart becomes diseased during...)

If the heart becomes diseased during its embryonic/fetal development, it can regenerate itself to such an extent that it is fully functional by birth, provided some of the heart cells remain healthy. Dr. Jrg-Detlef Drenckhahn of the Max Delbrck Center for Molecular Medicine (MDC) Berlin-Buch made this discovery together with colleagues from Australia. They were able to demonstrate in female mice that the healthy cells of the heart divide more frequently and thus displace the damaged tissue. "Hopefully, our results will lead to new therapies in the future," Dr. Drenckhahn said. "With the right signals, a heart that has been damaged for example through infarction might be stimulated to heal itself." (Developmental Cell, 15, 521-533, October 14, 2008)*.

For the heart to be able to beat, it needs energy. If the energy production in the heart cells is disturbed, then the embryo will actually die of heart dysfunction. But if only a portion of the cells is affected, this is not the case: With the aid of the remaining healthy cells, the embryo manages to regenerate the heart.

The scientists switched off a gene (Holocytochrome C synthase, abbreviated Hccs) in the developing hearts of mice a gene that is essential for energy production. Results showed that the embryos died when all cells in the heart were affected by the defective energy production. However, the animals that still had some healthy myocardial cells survived, and at the time of birth they had a heart that was fully able to function.

The gene Hccs is located on one of the sex chromosomes, the X chromosome. In contrast to male animals who have only one X chromosome, females have two X chromosomes. Some of the altered female mice have an X chromosome with the defective Hccs gene and one with the intact Hccs gene. However, in the cells of the female animals, only one X chromosome is active. Depending on which one is expressed, either healthy or diseased heart cells develo
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