Survey for paired-like homeodomain gene expression in the hypothalamus: restricted expression patterns of Rx, Alx4 and goosecoid.

Homeobox genes are important regulators of cellular identity. Several homeobox genes are known to be specifically expressed in subsets of neurons in the forebrain, exclusively, or in distinct combinations. In this study, we explored the expression of homeobox genes in the forebrain of the adult rat by a degenerate polymerase chain reaction cloning strategy. We identified the expression of 12 homeobox genes, several of which display a remarkable restricted expression pattern in the adult brain. We demonstrated the expression of goosecoid in a very small set of neurons in the hypothalamus. By using Otp as a marker, these goosecoid-positive cells were found to constitute a small area just beside the paraventricular nucleus. Furthermore, we found expression of Rx in the pineal gland, along with Alx4. Rx was additionally found in the posterior pituitary and in cells aligning the bottom of the third ventricle. These findings form a starting point to reveal functions of the described homeobox genes in the forebrain.