The mouse tissue plasminogen activator gene 5′ flanking region directs appropriate expression in development and a seizure-enhanced response in the CNS

Abstract

Tissue plasminogen activator (t-PA) is a secreted serine protease implicated in multiple aspects of development. In the adult rat brain, transcription of t-PA is an immediate-early response in the hippocampus following treatments that induce neuronal plasticity. To study the sequence elements that govern transcription of this gene, in situ analysis was used to define t-PA's temporal and spatial expression pattern in midgestation embryos. Transgenic mice were then generated carrying t-PA 5' flanking sequences linked to the E. coli lacZ gene. Constructs containing 4 kb of the flanking sequences (4.0TAMGAL) confer beta-galactosidase activity mostly to the same tissues that exhibit high levels of t-PA mRNA by in situ analysis. In 4.0TAMGAL embryos from embryonic day 8.5 (E8.5) to 13.5 (E13.5), the majority of expression observed is localized to neural ectoderm-derived tissues. beta-galactosidase activity is first detected in restricted neuromeres in the midbrain and diencephalon, at E8.5 and E9.5 respectively. At E10.5, transgene expression is observed in neural crest-derived cranial nerves and dorsal root ganglia, but not placode-derived cranial nerves. From E10.5 to E13.5, beta-galactosidase activity is observed in postmitotic neurons of the midbrain, spinal cord, neural retina and the developing olfactory system. beta-galactosidase activity is also detected in areas undergoing tissue remodeling such as the pinna of the ear, whisker follicles and the limbs. In adult mice, lacZ is expressed in the hippocampus and this expression was found to be enhanced upon seizure in the giant pyramidal neurons of CA3. These results reinforce the concept that t-PA plays a role in neurogenesis and morphogenesis, and identifies the promoter region that directs its transcriptional regulation both in development and in the CNS.