Function and Substrate Specificity of the Gibberellin 3β-Hydroxylase Encoded by the Arabidopsis GA4 Gene1

cDNA corresponding to the GA4 gene of Arabidopsis thaliana L. (Heynh.) was expressed in Escherichia coli, from which cell lysates converted [14C]gibberellin (GA)9 and [14C]GA20 to radiolabeled GA4 and GA1, respectively, thereby confirming that GA4 encodes a GA 3β-hydroxylase. GA9 was the preferred substrate, with a Michaelis value of 1 μm compared with 15 μm for GA20. Hydroxylation of these GAs was regiospecific, with no indication of 2β-hydroxylation or 2,3-desaturation. The capacity of the recombinant enzyme to hydroxylate a range of other GA substrates was investigated. In general, the preferred substrates contained a polar bridge between C-4 and C-10, and 13-deoxy GAs were preferred to their 13-hydroxylated analogs. Therefore, no activity was detected using GA12-aldehyde, GA12, GA19, GA25, GA53, or GA44 as the open lactone (20-hydroxy-GA53), whereas GA15, GA24, and GA44 were hydroxylated to GA37, GA36, and GA38, respectively. The open lactone of GA15 (20-hydroxy-GA12) was hydroxylated but less efficiently than GA15. In contrast to the free acid, GA25 19,20-anhydride was 3β-hydroxylated to give GA13. 2,3-Didehydro-GA9 and GA5 were converted by recombinant GA4 to the corresponding epoxides 2,3-oxido-GA9 and GA6.

Genome-wide gene expression profiles of the developing mouse hippocampus

We have analyzed the developmental molecular programs of the mouse hippocampus, a cortical structure critical for learning and memory, by means of large-scale DNA microarray techniques. Of 11,000 genes and expressed sequence tags examined, 1,926 showed dynamic changes during hippocampal development from embryonic day 16 to postnatal day 30. Gene-cluster analysis was used to group these genes into 16 distinct clusters with striking patterns that appear to correlate with major developmental hallmarks and cellular events. These include genes involved in neuronal proliferation, differentiation, and synapse formation. A complete list of the transcriptional changes has been compiled into a comprehensive gene profile database (http://BrainGenomics.Princeton.edu), which should prove valuable in advancing our understanding of the molecular and genetic programs underlying both the development and the functions of the mammalian brain.