IA-1, also known as INSM1, is an essential five zinc-finger transcription factor that while initially identified from an insulinoma cDNA library, is expressed in the developing nervous system. Specifically, IA-1 is expressed as early as E9.5 in mice in the fore-, mid- and hindbrain, spinal cord, retina, and olfactory bulb.  It is thought that IA-1 functions as a transcriptional repressor, and is a part of several signaling pathways including those of Notch and sonic hedgehog in addition to that of Ngn3 during pancreatic endocrine cell differentiation.  IA-1 is also expressed in multiple tumors, including the majority of neuroendocrine tumors tested so far as well as nearly 100% of all small cell lung carcinomas, indicating that IA-1 may be an important target in cancer therapy.