Mouse Glial Cells Missing a (mGCMa) belongs to a small family of transcription factors named after the prototypical GCM from Drosophila. mGCMa was expected to regulate gliogenesis, but instead found to be primarily expressed during development in trophoblasts of chorion and labyrinth. Its deletion causes abnormal placental labyrinth formation and results in embryonic lethality. Here we identify kidney and thymus as sites of mGCMa expression. In thymus, mGCMa is restricted to few small clusters of cells, in kidney to the S3 segment of proximal tubules. mGCMa expression is primarily postnatal, arguing for a role in organ function rather than organ development.