In fish it appears that this function may be regulated by Lgi1b. Recently we performed an extensive survey of Lgi1 expression in the developing mouse embryo and demonstrated that, at early stages of development, lgi1 GDC-0879 expressing cells also express nestin and doublecortin, suggesting a function in neural progenitor cells. It has been shown recently that MO knockdown of zebrafish nestin produces a very similar phenotype to that seen in the lgi1b morphants. Both morphants show smaller eye size and brain mass, which is attributable to increased apoptosis in both cases. The hydocephalus seen in the lgi1b morphants were also seen in the nestin morphants and neither morphant exhibits the seizurelike behavior seen in the lgi1a morphants. Nestin is an intermediate filament protein which interacts with vimentin and desmin to form part of the cellular cytoskeleton and is expressed primarily in neuroepithelial precursor cells and proliferating neural progenitor cells. Since LGI1 is a secreted protein, it is unlikely to interact directly with cytoskeletal proteins but the striking resemblance in phenotypes in the nestin and lgi1b morphants, together with the observation that Lgi1 is expressed in nestin expressing cells, suggests that the function of these two proteins may be interconnected. The phenotypic consequences of lgi1b knockdown involve abnormal development of the brain with increased apoptosis as well as abnormal eye development, suggesting an important role for this gene in the development of these organs. This observation is supported by the expression pattern for lgi1 defined by Gu et al using in situ hybridization. At 24 hours, lgi1b was expressed in presumptive telencephalic and diencephalic bands and the cranial paraxial mesenchyme By 48 hours lgi1b was expressed in the optic tectum, cerebellum and a zone of migratory neurons that originated from the rhombic lip as well as in the dorsal thalamus and the retinal ganglion layers. Generally, although some overlap with the expression of lgi1a, expression of lgi1b was dorsally restricted in the mid and hind brain which is consistent with the distribution of apoptosis seen in the lgi1b morphants. It is interesting that lgi1b expression is seen in subsets of migrating neurons since molecular and developmental analysis of the mammalian LGI1 gene also suggests a role in neuronal migration. Lgi1, however, is a secreted protein and it is not clear whether loss of function in morphants leads to a cell autonomous phenotype or whether the loss of protein function affects cells that would normally be responsive to its presence. The seizure-like behavior seen in lgi1a is very different to that seen in the lgi1b morphants and we are currently investigating whether there is an underlying electrophysiological basis of this difference. Both lgi1 morphants, however, show a sensitization to PTZ-induced hyperactivity.