Epigenetic changes in development are important in that the gene expression of cells that make up a particular organ or tissue type is often defined by epigenetic markers. Which of the following epigenetic regulations is known to cause more long-term gene silencing during the course of development?
A) chromatin remodeling B) DNA methylation C) histone modifications D) DNA ubiquitination
Activin is a protein that normally exists in a gradient within certain tissues in developing embryos. Certain undifferentiated cells cultured without activin produce epidermal cells. However, activin induces these same cells to adopt other fates (e.g., blood, muscle, heart), depending on the concentration of activin. Based on these observations, activin acts as a(n):
A) transcription factor. B) cell-surface receptor. C) morphogen. D) second messenger. E) activator.