Researchers demonstrate the importance of maternal genes for embryonic development
A team of French and American researchers have demonstrated how genes expressed by the mother affect the development of the growing embryo. Serotonin is a neurotransmitter which is involved in a number of physiological processes, including the sleeping cycle, the control of body temperature and blood pressure and sexual behaviour. Serotonin also plays an important role in embryonic development, notably in the central nervous system. However, researchers have been unable to find a site in the early stage embryo where serotonin is made, leading them to wonder if it was not coming from the mother. Now a team of researchers, lead by the French National Scientific Research Centre, has found that this is indeed the case. Their findings are published online by the Proceedings of the National Academy of Sciences (PNAS). Using genetic crosses, the researchers created situations where mother mice whose serotonin genes had been knocked out were carrying pups with normal serotonin genes, and vice-versa. They found that the genes of the mother had a greater influence on the health of the pups that the pups' own genes. Analysis of the embryos growing inside mothers with normal serotonin levels revealed them to be indistinguishable from normal mouse embryos. However, the embryos of mothers whose serotonin levels were abnormally low were smaller that average and had brain abnormalities. 'The results indicate that the genotype of the mother influences embryonic development regardless of genotype of the embryo,' write the researchers. 'In addition, the observations strongly support the idea that a maternal source of serotonin is necessary for normal development.' The work has important implications for the treatment of a number of medical conditions. For example, autism has been linked to high levels of serotonin, and the researchers suggest that variations in maternal serotonin levels in early pregnancy could exert subtle effects on brain development. With this in mind, they note that it could be prudent to check women's serotonin levels and genotype during pregnancy. The researchers believe their research could also help to understand the causes of Irritable Bowel Syndrome (IBS), which affects 20% of the population. Large amounts of serotonin are produced in the bowel, and IBS has been linked to problems with serotonin uptake. They note that in the embryo, the serotonin uptake system develops before the embryo starts creating its own serotonin, so for the system to be affected by serotonin, that serotonin must come from the mother. Looking to the future, the researchers pose a number of issues which still remain to be addressed, for example how long maternal serotonin is available to embryos and how it is transferred to the foetus.
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