Protein secretion by cell cultures: An essential biological issue

All the tissues cultures in vitro secrete a vast array of molecules into the culture media. The secretion of high molecular weight compounds, such as proteins, has showed an active role in different biological phenomena. Indeed, several reports have made allusion to the extracellular proteins as a pivotal point in the initiation of the signal cascade which induces the early steps of somatic embryogenesis. Some protein markers of these phenomena have been identified in carrot. However, little is known about the biological function of the extracellular proteins secreted during this process. The models already suggested always fall in speculation and controversy. In this review, a comprehensive analysis of extracellular proteins secreted into the culture media is made, with an emphasis in those that could be involved in the early induction of somatic embryogenesis.