Despite the relatively simplified organization of the olfactory epithelium (OE), our understanding of the factors that regulate its cellular diversity is limited. Genetic and localization studies suggest that Notch signaling may be important in this process. We characterize here a population of Notch1 (+) olfactory basal cells in embryonic mice that coordinately express both the Notch effector Hes5 and the glycosyltransferase Lfng. These cells are distinct from Mash1(+) neuronal precursors, but give rise to sensory neurons, suggesting that Notch1 signals may in part function to maintain a neurogenic progenitor pool. Furthermore, Lfng(+) cells also generate a population of cells in the migratory mass that appear to be ensheathing glial precursors, indicating potential multipotency in these progenitors. The Notch ligand Dll4 is expressed by basal OE cells that are interspersed with Notch1(+) progenitors during later OE neurogenesis. In contrast, mice deficient in Dll1 exhibit a smaller OE and a loss of Hes5 expression, indicating an earlier function in olfactory progenitor cell development. Taken together, these results further support a role for Notch signaling in the regulation of olfactory neurogenesis and cell diversity.

Goosecoid (gsc) is an evolutionarily conserved homeobox gene expressed in the gastrula organizer region of a variety of vertebrate embryos, including zebrafish, Xenopus, chicken and mouse. To understand the role of gsc during mouse embryogenesis, we generated gsc-null mice by gene targeting in embryonic stem cells. Surprisingly, gsc-null embryos gastrulated and formed the primary body axes; gsc-null mice were born alive but died soon after birth with numerous craniofacial defects. In addition, rib fusions and sternum abnormalities were detected that varied depending upon the genetic background. Transplantation experiments suggest that the ovary does not provide gsc function to rescue gastrulation defects. These results demonstrate that gsc is not essential for organizer activity in the mouse but is required later during embryogenesis for craniofacial and rib cage development.