Cell protection in early life
December 7, 2018
Life processes occur at scales ranging from very small (e.g., enzyme activity) to very large (e.g., ocean nutrient cycling) and biodiversity can ultimately be affected by processses occurring at any scale. In a study by Alderman et al. (2018) they looked at the effects of physiological stress on cells, in other words, processes that take place at the small end of the scale.
The researchers were interested in the corticotropin-releasing factor (CRF) system, a biochemical system which is present in embryos but whose possible function was unknown. At later life stages, the CRF system plays crucial roles in modulating stress, such as through effects on caspase-3, a small enzyme that induces cell death through a process called apoptosis. There are essentially two ways in which cells can die, either through apoptosis, which is a controlled process and is important in development (e.g., tail resorption in tadpoles), or through necrosis, which is uncontrolled and can have detrimental effects on surrounding cells and tissues. Under environmental conditions that create stress however, apoptosis can be activated and disrupt normal development.
Their study used zebrafish (Danio rerio) embryos, a species of fish native to South Asia that is commonly used as a model organism to study vertebrate biology and address questions ranging from startle behaviour in fish to cancer in humans. In order to mimic physiological stress, Alderman et al. (2018) exposed the lab-reared embryos to elevated water temperatures (i.e., heat shock) and manipulated the CRF system in a way that facilitated detecting whether or not the system affected caspase-3 activity. They then measured CRF gene expression, caspase-3 activity, and recorded embryo mortality.
Their results showed that embryonic zebrafish exposed to the stress of heat shock had greater caspase-3 activity however, this activity was reduced by the CRF system. Mortality of embryos that occurred during the experiment due to heat shock was deemed to be related to necrotic cell death rather than apoptosis. With this study, Alderman et al. (2018) demonstrate for the first time that the CRF system protects cells from apoptotic cell death during early development of a vertebrate species when placed under conditions of stress. Furthermore, this new information can add to our understanding of the impacts of environmental stressors on species such as fish that develop externally and are therefore directly exposed to environmental conditions.
Read full article (journal subscription required):
Alderman SL, Leishman EM, Fuzzen MLM, and Bernier NJ. 2018. Corticotropin-releasing factor regulates caspase-3 and may protect developing zebrafish from stress-induced apoptosis. General and Comparative Endocrinology. 265:207-213.