Gene trapping in mouse embryonic stem cells is an efficient method for identifying new genes and examining their functions. This method has been used in an effort to identify some novel genes involved in mouse development. In the present paper, one such gene named IZP6 is reported. Expression of the IZP6 gene, as monitored by beta-galactosidase expression in heterozygous mice, was detected in a developmentally regulated fashion: the expression pattern has two phases during the embryogenesis. In the first phase, from embryonic day 11.5 (E11.5) until E14.5, the reporter gene is mainly expressed in the forebrain. In the second phase, from E15.5 until birth, expression in the forebrain becomes weaker but is still observed in the olfactory bulb and the skin around the eyes, nose, limbs and tail. Thus, IZP6 gene expression changes from the central nervous system (the first phase) to the peripheral tissues (the second phase) during development. The IZP6 gene encodes a protein of 228 amino acids. Analysis of the secondary structure of the IZP6 protein revealed four hydrophobic regions, indicating that the IZP6 protein is a four transmembrane region protein. These results suggest that IZP6 is a transmembrane protein related to neurogenesis in the mouse.