Tissue growth

This suggests that cell proliferation in skin stem cells within the basal layer is likely to be mechanically controlled to ensure that the skin covers the surface of the entire body.

Cell proliferation in skin stem cells within the basal layer can be driven by the mechanically-regulated YAP/TAZ family of transcriptional co-activators, which bind to TEAD-family DNA binding transcription factors in the nucleus to activate target gene expression and thereby drive cell proliferation.

For other animal tissues, such as the bones of the skeleton or the internal mammalian organs intestine, pancreas, kidney or brain, it remains unclear how developmental gene regulatory networks encoded in the genome lead to organs of such different sizes and proportions.

Although different animal tissues grow at different rates and produce organs of very different proportions, the overall growth rate of the entire animal body can be modulated by circulating hormones of the Insulin/IGF-1 family, which activate the PI3K/AKT/mTOR pathway in many cells of the body to increase the average rate of both cell growth and cell division, leading to increased cell proliferation rates in many tissues.

Gradients of Wnt signaling pathway activity appear to have a fundamental role in maintaining proliferation of stem and progenitor cells, at least in the intestine, and possibly also in skin.