Written by: Jasmine Biju
The epidermis is the outermost layer of the skin. It has numerous important functions from protecting your body from pathogens to keeping the skin hydrated. A vital function of the epidermis in particular is the regeneration of skin cells. As important as it is, scientists have struggled over the years to discern the molecular mechanisms involved in the self-renewal and differentiation cellular processes. Differentiation refers to the maturation of a young and unspecialized cell which is driven by genetics. However, a research team from Northwestern University has deduced that a protein called CDK9 is fundamental in the skin regeneration process.
CDK9 acts as a molecular switch. In epidermis cells, this switch is on. However, in stem cells, this switch is off. Stem cells are undifferentiated, or immature, from which other cells with specialized functions can be produced via differentiation. In this case, when CDK9 is switched on, stem cells begin to develop barrier-like properties which are necessary for the skin. The skin is a part of the body’s first line of defense, or the innate immune system. There are two main parts of the immune system: the innate immune system and the adaptive immune system. The innate immune system is the body’s physical defenses, including the skin, mucus, and wax. So, skin cells specifically specialize in protecting from hazardous substances and harmful microorganisms.
Skin stem cells have two pathways of choosing: self-renewal, which refers to the replication of these cells, or differentiation, maturing into specialized cells. Skin regeneration is dependent on the decision of the skin stem cells to either engage in differentiation or not. Xiaomin Bao, an assistant professor of dermatology at Northwestern University, and her team discovered a link between regeneration and the activation of CDK9, which initiates the differentiation process.
CDK9 stands for cyclin-dependent kinase nine. The research team observed that when this molecular switch is off, genes that are controlled by CDK9 remain inactivated. However, when this molecular switch is on, the corresponding genes are activated. When an external signal is received by a stem cell, the activated CDK9 quickly causes rapid-response genes to be expressed. This essentially helps redetermine the cell development towards differentiation. After dead skin cells turn over, these newly developed skin cells are able to take their place.
The epidermis has a cycle of constantly turning over dead skin cells to reveal new ones. This process is essential in protecting from external threats and hydrating the skin. The discovery made by the Northwestern research team has made it possible to attribute the skin regeneration process to the molecular switch, CDK9.
References:
Image Source: Wikipedia
Fellman, M. “Scientists identify key mechanism controlling skin regeneration.” Northwestern Now, Northwestern, 2022.
Sarah M. Lloyd, Daniel B. Leon, Mari O. Brady, Deborah Rodriguez, Madison P. McReynolds, Junghun Kweon, Amy E. Neely, Laura A. Blumensaadt, Patric J. Ho, Xiaomin Bao. “CDK9 activity switch associated with AFF1 and HEXIM1 controls differentiation initiation from epidermal progenitors.” Nature Communications, 2022.
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