Transient expression of glutamate decarboxylase and gamma-amino butyric acid in embryonic lens fibers of the rat.

We have determined the localization and developmental expression of glutamate decarboxylase (GAD67) in the rat lens. Immunofluorescence experiments showed that GAD67 was transiently expressed in the nuclear fiber cells of the lens between embryonic days (E) 15 and 20, with maximal immunostaining occurring on E17 and E18. gamma-amino butyric acid (GABA) co-localized with GAD67 in the embryonic nuclear fiber cells. Reverse transcription-polymerase chain reaction (RT-PCR) tests showed that at least three alternatively spliced forms of GAD67 mRNA, including mRNAs with and without the I80 and the I86 insert, were transiently co-expressed with GAD67 in the embryonic lens. The major GAD67 protein in the lens was 67 kDa. We conclude that enzymatically active GAD67 is transiently expressed in the lens nuclear fiber cells of the embryonic rat. The transient expression is regulated by transcriptional and/or posttranscriptional processes. We speculate on the basis of possible common gene regulatory elements for glutamate and ornithine decarboxylases and the involvement of these enzymes with polyamine synthesis, that the transient expression of GAD67 may be connected to nuclear and/or DNA breakdown during lens fiber cell differentiation.