Spatial, temporal and subcellular localization of islet-brain 1 (IB1), a homologue of JIP-1, in mouse brain

Islet-brain 1 (IB1) was recently identified as a DNA-binding protein of the GLUT2 gene promoter. The mouse IB1 is the rat and human homologue of the J un-interacting protein 1 (JIP-1) which has been recognized as a key player in the regulation of c-Jun amino-terminal kinase (JNK) mitogen-activated pr otein kinase (MAPK) pathways. JIP-1 is involved in the control of apoptosis and may play a role in brain development and aging. Here, IB1 was studied in adult and developing mouse brain tissue by in situ hybridization, Northe rn and Western blot analysis at cellular and subcellular levels, as well as by immunocytochemistry in brain sections and cell cultures. IB1 expression was localized in the synaptic regions of the olfactory bulb, retina, cereb ral and cerebellar cortex and hippocampus in the adult mouse brain. IB1 was also detected in a restricted number of axons, as in the mossy fibres from dentate gyrus in the hippocampus, and was found in soma, dendrites and axo ns of cerebellar Purkinje cells. After birth, IB1 expression peaks at postn atal day 15. IB1 was located in axonal and dendritic growth cones in primar y telencephalon cells. By biochemical and subcellular fractionation of neur onal cells, IB1 was detected both in the cytosolic and membrane fractions. Taken together with previous data, the restricted neuronal expression of IB 1 in developing and adult brain and its prominent localization in synapses suggest that the protein may be critical for cell signalling in developing and mature nerve terminals.