ABSTRACT
On the cellular level, vitamin A and its major active metabolite, all-trans-retinoic acid (RA), which acts as a morphogen, enable transcriptional regulation of RA-responsive genes through a well-known RA signaling pathway. RA signaling is a tremendously complex and highly regulated process, being responsible for many aspects of cellular function. Differentiation is a highly controlled molecular process with numerous molecular and cellular events. Programmed cell death, or apoptosis, is a precisely regulated cellular process which enables proper organogenesis during embryonic development and maintenance of normal tissue homeostasis in adulthood. On the molecular level, apoptosis induction by RA occurs through the signaling cascade, including cellular RA-binding protein 2 and retinoic acid receptor. The involvement of retinoids and retinoic acid, as their final effector in regulation of most of the critical cellular processes, is crucial, and the evidence of the complexity of RA signaling regulation and the interplay between its different downstream targets is continually developing.
