DYNAMIC EXPRESSION SUGGESTS MULTIPLE ROLES OF THE EPH FAMILY RECEPTORBRAIN-SPECIFIC KINASE (BSK) DURING MOUSE NEUROGENESIS

The eph family ligands and receptors have been implicated in mediating topographic neuron-target interactions. We recently isolated Bsk, a n ew member of the eph family receptors, and showed that it is expressed primarily in the brain. To investigate the role of Bsk in the develop ment of the nervous system, we examined the temporal and spatial patte rns of Bsk expression using in situ hybridization. We report here that Bsk expression exhibits dynamic changes during embryogenesis. In earl y embryos, Bsk is widely transcribed in the nervous system, including the forebrain, midbrain, hindbrain and spinal cord. Bsk expression in the midbrain, hindbrain and spinal cord, however, gradually decreases while in the forebrain increases over time. By embryonic day 18, the m ost intense Bsk expression was found in the limbic system. High levels of the expression in the limbic system persisted throughout post-nata l development and remained stable in the adult up to 24 month. The top ography of Bsk expression is in the form of gradients in several regio ns of the brain, including the lateral septum, spinal cord, as well as the hippocampus. Selective expression was also observed in Purkinje c ells. Our findings on the topography of Bsk expression provide support to potential roles of Bsk in topographic projection. Our analyses fur ther suggest that there may be other novel functions of Bsk in early n eurogenesis in addition to potential roles in topographic mapping. (C) 1997 Elsevier Science B.V. All rights reserved.