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Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

Developmental Biology - Telomere Length

Born to Be Young?

Mom's prenatal thyroid hormones influence an infant's biological 'age' at birth...

The environment provided by a mother's body during embryonic and fetal development has major consequences on her infant's health and overall lifespan.

This may be the result of maternal stress hormones shortening the length of fetal telomeres. Telomeres are the protective 'end caps' made up of folded DNA, located on the tips of each chromosome. Telomere length serves as a marker of an individual's 'biological age'

Telomeres normally shorten as we age, indicating a higher incidence of disease along with higher mortality risk. Prenatal exposure to maternal stress hormones during embryo development, has previously been found to result in shorter telomeres and accelerates cell ageing.

A new study funded by the Academy of Finland and the Turku Collegium for Science and Medicine, Finland, and published in the journal of The Royal Society, manipulated prenatal exposure to maternal thyroid hormones by injecting eggs from birds as the model species.
"The telomere biology in humans is closer to the telomere biology in birds - than to other traditional laboratory animal models. In both humans and birds, telomere length is measured in a minimally-invasive way using small blood samples."

Antoine Stier PhD, Turku Collegium, University of Turku (Finland) and main author of the published research.

Authors of the study had reason to expect shorter telomeres in chicks born from eggs injected with thyroid hormones. But, were quite surprised to find those same chicks actually exhibited longer telomeres right after birth.
"Based on the natural decline in telomere length observed with age in the Collared Flycatcher bird population, we estimate chicks hatching from thyroid hormone injected eggs - were approximately 4 years 'younger at birth' than chicks hatched from control eggs."

Suvi Ruuskanen PhD, Turku Collegium, University of Turku (Finland).
Although the underlying molecular mechanisms of such effects remain to be discovered, these new findings suggest prenatal thyroid hormones might have a role in setting individual 'biological age' at birth.
"Considering controversies surrounding gene therapy trials in humans to elongate telomeres as an anti-ageing therapy — this discovery opens potential avenues to better understand the influence of telomere elongation using animal models."

Antoine Stier PhD.
The study was conducted on a long-term monitored population of wild collared flycatcher breeding in Gotland island, and relied on extensive collaborations with the University of Uppsala (Sweden), Lyon, Glasgow and Aberdeen.

The underlying mechanisms of the lifelong consequences of prenatal environmental condition on health and ageing remain little understood. Thyroid hormones (THs) are important regulators of embryogenesis, transferred from the mother to the embryo. Since prenatal THs can accelerate early-life development, we hypothesized that this might occur at the expense of resource allocation in somatic maintenance processes, leading to premature ageing. Therefore, we investigated the consequences of prenatal TH supplementation on potential hallmarks of ageing in a free-living avian model in which we previously demonstrated that experimentally elevated prenatal TH exposure accelerates early-life growth. Using cross-sectional sampling, we first report that mitochondrial DNA (mtDNA) copy number and telomere length significantly decrease from early-life to late adulthood, thus suggesting that these two molecular markers could be hallmarks of ageing in our wild bird model. Elevated prenatal THs had no effect on mtDNA copy number but counterintuitively increased telomere length both soon after birth and at the end of the growth period (equivalent to offsetting ca 4 years of post-growth telomere shortening). These findings suggest that prenatal THs might have a role in setting the ‘biological' age at birth, but raise questions about the nature of the evolutionary costs of prenatal exposure to high TH levels.

Antoine Stier , Bin-Yan Hsu , Coline Marciau , Blandine Doligez , Lars Gustafsson , Pierre Bize and Suvi Ruuskanen.

Published by the Royal Society. All rights reserved.

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Nov 16 2020   Fetal Timeline   Maternal Timeline   News

Flycatcher egg being illuminated in order to inject thyroid hormones specifically into the egg yolk.
CREDIT Tom Sarraude.

Phospholid by Wikipedia