What does maternal influence mean?
Gestation in mammals, the period between conception and birth, sees a single cell develop into an immature organism capable of surviving outside of the womb with a varying degree of independence. Immaturity at birth means that development and maturation of a range of organ systems, including the brain, straddles sharply contrasting physical and nutritional environments, the first in utero and the second postnatal. Postnatal environment is potentially very variable, in utero environment less so. However, although buffered from the full vagaries of the ambient environment, the developing fetus is reliant on the mother for nutrition. It will consequently be exposed to, and sensitive to, maternal nutritional signals that represent the integration of the internal and external environments during the highly coordinated processes of development. Premature birth is an additional challenge to the maturing animal with untimely exposure to the ambient environment and less certain nutrition.
Why is maternal influence important?
Sub-optimal development as a consequence of nutritional or other insult/stressor either before birth and/or during critical early years can have deleterious consequences for organ development which may or may not be fully compensated for later, as well as for the metabolism and health of the resultant offspring both in early life and in the longer term. Nutritional experiences in utero can lead to adaptation to the predicted postnatal environment that is designed to be advantageous but may prove not to be, depending on the actual lifetime environment. This is illustrated by the consequences of the famine winter in the Netherlands during World War II whereby children born during the famine developed higher rates of obesity, diabetes and other health problems. These outcomes are represented in what has become known as the ‘thrifty phenotype’ hypothesis. Childhood obesity is increasing at an alarming rate, with epidemiological and animal study evidence implicating maternal diet during pregnancy, and maternal obesity, in lifelong risk of developing obesity and diabetes. Increasing recognition of this relationship with maternal nutrition is reflected in developing public health strategies addressing pregnancy and early years.
How does maternal influence work?
How does early life nutrition influence lifelong health? At its most severe, and if the nutritional insult occurs during a critical developmental period, disruption in organ development may be permanent. The brain is the most complex organ in the human body. Brain structure may be particularly vulnerable at times of rapid growth, with consequences visible using imaging techniques. More subtle anatomical changes in the brain may also accompany early life nutritional and hormonal challenges. These may include changes to the density of connections that develop between individual brain nuclei that may control hunger and satiety. Hormonal environment in utero and in early postnatal life, such as circulating glucocorticoids, can also have a programming effect. The early life environment can also influence lifelong phenotype and health through heritable and/or acquired changes in the expression of genes in the absence of changes in DNA sequence (epigenetics). Changes to the epigenetic code, which can determine whether or not genes are expressed, can result from either the addition of methyl groups to DNA cytosine bases, or the post-translational modification of histone proteins by the addition of methyl or acetyl groups. Changes in methyl status during gestation provide a mechanism for environment, including nutrition, to influence subsequent gene expression. Epigenetic changes can also result from mother-infant interactions, and through paternal influence across generations.