Apart from what is known about the role of Vitamin A and its active form called retinoic acid in vision, the role of this vitamin is also seen in several aspects of development invertebrates. These functions range from division to differentiation. According to research published in Dev Cell in 2010 by Li and team; retinoic acid functions the development of the cardiovascular and central nervous systems as well as differentiation of muscle cells and cartilage. This patterning of embryonic or embryos cells due to Vitamin A is due to the binding of retinoic acid to change the expression of target genes. This binding is due to the interaction of factors to the corresponding promoters called retinoic acid response elements (RAREs) in the genes controlled by the vitamin.
According to Zile and the team in Nutrients; the first functioning system to develop in the vertebrate embryos is that of the heart. This requires optimum levels of Vitamin A as either low or high amounts can lead to defective cardiovascular development.
The development of the heart in early stages can be compared across vertebrates, the use of appropriate models such as that of avian species can offer insights to understanding development. In this case, retinoic acid becomes crucial for not only the survival but also the developed morphology of the heart. According to early research in Developmental Biology by Dersch and team, during the 4–5 somite stage, deficiency of Vitamin A leads to the sudden closure of the newly developing inflow tracts and failure of differentiation of the sino-atrial cells. Such embryos die within 4 days due to such abnormal hearts and central nervous systems. When retinoic acid is administered to the embryos during this stage, these abnormalities can be prevented.
In order to develop a system to study the role of vitamin A in development, a team led by Cakstina published the establishment of primary heart cultures in BMC developmental biology in 2014. The development of vertebrate hearts and their association with retinoic acid have not been explored under physiological conditions. Hence, the approach of the team involved the use of in vitro culture instead of in vivo models that require the use of live embryos from animals.
The approach involved incubating newly fertilized eggs at 37°C following 36 to 42 hours of incubation to obtain heart forming regions that were placed on plates. The development of cardiomyocytes was observed on the Endo-Grow medium after 24 hours. These cells expressed the appropriate markers such as VEGF-A along with transcription factors GATA4 and Nkx2.
Among the transforming growth factor-beta (TGFβ) family of cytokines, the correct development of the heart requires TGFβ2. This signaling is in turn dependant on retinoic acid. The exposure of the culture to retinoic acid increased the levels of vascular endothelial growth factor (VEGF-A): a gene controlled by retinoic acid by almost two-fold showing the role of this molecule in heart development.
Thus, primary cultures offer such novel insights into the field of embryo development such as the effect of retinoic acid on embryogenesis. Thus, the mechanisms behind the development of the vertebrate heart can be unlocked using cultures.
Li P, Pashmforoush M, Sucov H. Retinoic acid regulates differentiation of the secondary heart field and TGFβ-mediated outflow tract septation. Dev Cell. 2010;18:480–485.
Zile MH. Vitamin A – not for your eyes only: requirement for heart formation begins early in embryogenesis. Nutrients. 2010;2:532–550.
Dersch H, Zile MH. Induction of normal cardiovascular development in the vitamin A- deprived quail embryo by natural retinoids. Developmental Biology. 1993;160:424–433.
Cakstina, I., Riekstina, U., Boroduskis, M., Nakurte, I., Ancans, J., Zile, M. H., & Muiznieks, I. (2014). Primary culture of avian embryonic heart forming region cells to study the regulation of vertebrate early heart morphogenesis by vitamin A. BMC developmental biology, 14, 10.