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 gl utamate decarboxylase (GAD67) in the rat lens. Immunofluorescence expe riments showed that GAD67 was transiently expressed in the nuclear fib er cells of the lens between embryonic days (E) 15 and 20, with maxima l immunostaining occurring on E17 and E18. gamma-amino butyric acid (G ABA) co-localized with GAD67 in the embryonic nuclear fiber cells, Rev erse transcription-polymerase chain reaction (RT-PCR) tests showed tha t 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 i n 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 c ommon gene regulatory elements for glutamate and ornithine decarboxyla ses and the involvement of these enzymes with polyamine synthesis, tha t the transient expression of GAD67 may be connected to nuclear and/or DNA breakdown during lens fiber cell differentiation. (C) 1995 Wiley- Liss, Inc.