PROTEASE NEXIN-I (PNI) IN MOUSE-BRAIN IS EXPRESSED FROM THE SAME GENEAS IN SEMINAL-VESICLE

Protease nexin I (PNI), a serine protease inhibitor (serpin), is the m ost potent tissue inhibitor of thrombin. In the nervous system, PNI ha s been shown to participate in processes related to synaptic plasticit y and neuronal survival. We assigned the human gene for PNI (PI7) to c hromosome 2q33-35, and to syntenic regions in mouse chromosome 1. Othe rs showed that a similar serpin was expressed in mouse seminal vesicle , which presented the possibility of a ''duplicate'' gene. The data al so raised controversy over the quantity of PNI mRNA expressed in the b rain vs peripheral tissues, such as seminal vesicle. In order to furth er our investigations of PNI regulation and its influence on neuronal survival and neuroprotection, it was necessary to confirm whether the nexin observed in mouse brain samples was identical to the published p rotease nexin I sequences. To accomplish this, we performed DNA sequen ce analysis of cDNAs made from RNAs isolated from mouse forebrain and hindbrain as well as from seminal vesicle. These confirmed the identit y of the mouse PNI gene (SPI4) in brain and peripheral tissues. Furthe rmore, Northern hybridization studies indicated that the PNI message i s present at lower levels in the adult brain compared to the adult sem inal vesicle. Western immunoblotting showed no differences between bra in and seminal vesicle PNI proteins. The PNI cDNAs generated will serv e as useful probes for the continued characterization of the serpin:pr otease balance as it relates to nerve cell function.