A NOVEL BRN3-LIKE POU TRANSCRIPTION FACTOR EXPRESSED IN SUBSETS OF RAT SENSORY AND SPINAL-CORD NEURONS

Brn3a and Brn3b are mammalian members of the POU class of transcription factors. They are closely related to each other and to Unc86, which determines the normal development of certain cells, including mechanoreceptive sensory neurons in Caenorhabditis elegans. We screened a rat dorsal root ganglion (DRG) cDNA library at moderate stringency with a Brn3a POU-domain probe and identified a novel transcript encoding a POU protein that we have named Brn3c. Brn3c closely resembles Brn3a and Brn3b in its POU-domain and thus helps define a family of Unc86-related mammalian POU factors. Both Brn3a and Brn3c are expressed only in the central and peripheral nervous systems. In the neonatal rat, northern blots revealed a 3.6 kb Brn3a transcript in DRG, spinal cord and hindbrain, and a 2.6 kb Brn3c transcript in DRG and spinal cord. In situ hybridization showed that most DRG neurons express Brn3a whereas only a small subset of neurons expresses Brn3c. In the spinal cord, Brn3a is expressed by many dorsal horn neurons. In contrast, Brn3c is expressed by a very small number of cells in laminae 4/5 of the dorsal horn. These data suggest that Brn3-related POU factors may be involved in the development or function of particular subclasses of sensory and spinal cord neurons.