An international article led by researchers from the Faculty of Biology at the Technion indicates the influence of the environment on human fertility patterns
Surprising data regarding the influence of the environment on human fertility patterns: an international review article by researchers from the Technion and two British universities reveals the flexibility that exists in this context at the age of sexual puberty and the influence of the childhood environment on the duration of the female fertility period.
The article published in Nature Reviews Endocrinology was led by Prof. Filipa Melamed and PhD student Ben Bar-Sheda with Dr. Sergi Rodnizki, Dr. Lilach Panoeli and Prof. Ariel Kaplan, all from the Faculty of Biology at the Technion. Overseas, the anthropologist Prof. Gillian Bentley from the University of Durham and the biologist Prof. Reinhard Stöger from the University of Nottingham participated in the research.
The fertility of women and men begins in adolescence with sexual maturation. The female fertility period is limited in time and ends in the fifth decade of a woman's life, however the exact ages of the beginning of fertility and the end of fertility (menopause) vary greatly between populations. In the Western world, the childbearing age starts relatively early and ends late, so the childbearing period is longer than in the third world. Such a change also occurs on the timeline - the (average) age of first menstruation in Western Europe, for example, dropped in the last century from 16 to 13 years.
In the current article, the authors point out that in regards to fertility patterns, the environmental influence "wins" over genetics. This conclusion is partly based on a comparison between women who immigrated from the Third World to the West at different ages. The researchers say that girls or women who immigrated at a late age maintained the "poor" fertility pattern - a short fertile period, which starts late and ends early; Whereas women who immigrated as children before the age of 8-6 adopted the western local pattern - high levels of the sex hormone progesterone and a long fertile period. In other words, if the girls are exposed to the new environment at a young age, the environment causes them to "abandon" the maturation paths typical of their homeland in favor of the paths that characterize their new country. On the other hand, at a later age it has no effect even after many years in the new country. This means: fertility patterns are mainly determined by the influence of the environment during childhood.
Prof. Melamed's research group focuses on molecular mechanisms that are responsible for this variation, and in particular on the role of the epigenome in controlling the reproductive system in different environments. Epigenetics, a term coined by the biologist Conrad Weddington in 1942, deals with the genetic effects that are not manifested as a result of changes in the sequence of the DNA, but rather from chemical additions that lead to differences in the packaging of the DNA - the chromatin. The form of DNA packaging in chromatin is very significant, as it affects gene expression. The epigenome profile is affected by many factors such as nutrition, inflammation and even stressful situations, factors that may lead to the reprogramming of physiological systems, including the reproductive system.
According to Prof. Melamed, "The chromatin determines which genes will be exposed to the genetic reading mechanisms and thus will be activated - and which genes will remain switched off. Today we know how to carry out very precise manipulations of chromatin in the laboratory and see how they affect the expression of certain genes. We have already identified genes that are particularly sensitive to the environment - genes that undergo epigenetic changes in childhood - and we also studied this in a mouse model of inflammation before puberty. These changes share in changing the properties of the reproductive system."
As mentioned, emigrating to the West at a young age leads to a longer fertile period, which indicates a slowing down of the rate of egg loss. According to Prof. Melamed, "When we fully understand the molecular mechanism, we will be able to achieve the extension of the fertility period also through proactive and artificial intervention in the chromatin." Beyond scientific curiosity, these studies have extensive applied potential, since fertility patterns affect many processes in the body, including aging, senile diseases, cancerous developments and bone depletion (osteoporosis).
The message: interdisciplinary research
Prof. Melamed emphasizes that beyond the specific article and its important findings, "the connection made here between different research teams emphasizes the need to combine different approaches and different areas of expertise - human anthropology, bioinformatics and big data, experiments, molecular biology and even biophysics. That's why such studies are not possible without such interdisciplinary cooperation."
The research was supported by BBSRC/ESRC grants intended for interdisciplinary epigenetic research and by the Israel National Science Foundation (ISF).
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