Complex sentence: An example of an environmental factor is the morphogen sonic hedge hog (Shh), which has been shown to repress the differentiation of precursor cells into retinal ganglion cells Sanes, D. H., T. A. Reh, and W. A. Harris.
Split into simpler sentences: An example of an environmental factor is the morphogen sonic hedge hog (Shh). Shh has been shown to repress the differentiation of precursor cells into retinal ganglion cells Sanes, D. H., T. A. Reh, and W. A. Harris.