Mice lacking IGF-I and LIF have motoneuron deficits in brain stem nuclei.

We analyzed the neural embryonic phenotype of single and double-mutant mice for insulin-like growth factor-I (IGF-I) and leukemia inhibitory factor (LIF). The anatomical structure of the hippocampus, the cerebellum, and the olfactory epithelium, regions showing expression of both factors and their receptors, appeared largely normal in all mutant mice. In the fimbria and the spinal cord, similar patterns of glial fibrillary acidic protein (GFAP)-expressing astrocytes were found in wild-type and mutant mice. In contrast, single Igf-I and double-mutant mice showed a significant reduction in the number of trigeminal and facial motoneurons, whereas mice lacking LIF showed a significant reduction of trigeminal motoneurons. These results suggest that IGF-I and LIF regulate cooperatively motoneuron numbers in specific brain stem nuclei.