THE DEVELOPMENTAL EXPRESSION IN RAT OF PROTEASES FURIN, PC1, PC2, ANDCARBOXYPEPTIDASE-E - IMPLICATIONS FOR EARLY MATURATION OF PROTEOLYTICPROCESSING CAPACITY

The genes encoding mammalian subtilisin-like endoproteases furin, PC1, and PC2 have been isolated and are implicated in endoproteolytic clea vage of precursor molecules, which is a key step in posttranslational maturation of pro-proteins and neuropeptide precursors. Following endo proteolytic cleavage, the carboxyl-terminal basic amino acid residues are removed by carboxypeptidase E (CPE). We have examined the expressi on of these genes during rat development by in situ hybridization and compared their expression patterns to those of potential substrates. I n the primitive streak stage of embryogenesis (e7) furin is expressed in both endoderm and mesoderm. This overall expression pattern is main tained until e10, when a distinctly higher level of furin expression i s observed in the heart and liver primordia. In mid- and late gestatio nal stages furin is broadly expressed in the peripheral tissues, and, therefore, may contribute to the proteolytic processing of numerous fe tal proproteins, such as the precursors for natriuretic factors in hea rt and IGF-II throughout the embryo. In contrast, the expressions of P C1 and PC2 are initiated much later (e13) and are mainly confined to t he developing nervous system, but with distinct spatial distributions. At midgestational ages, PC1 mRNA is mainly expressed in the hypothala mus and peripheral ganglia, while PC2 is expressed not only in these t issues but also in the thalamus, midbrain, pens, medulla oblongata, co rtical plate, and spinal cord. Besides neuropeptide precursor processi ng in the nervous system, PC1 and PC2 may also be involved in the prot eolytic processing in additional regions as evidenced by the finding t hat both PC1 and PC2 mRNAs are expressed in the embryonic pituitary an d pancreas. CPE mRNA is expressed in both neural tissues and some non- neural tissues. In the developing nervous system, the expression of CP E encompasses all the regions where PC1 and PC2 are expressed and in f act includes most brain regions as neurogenesis proceeds. CPE mRNA is also expressed in some peripheral tissues, such as the embryonic heart and cartilage primordia, and in some cases its expression overlaps wi th furin expression. Thus, CPE may functionally collaborate during dev elopment with the subtilisin family of endoproteases in the completion of proteolytic processing of neuropeptide precursors in the nervous s ystem and proproteins in the peripheral tissues. In the pituitary, the endoproteolytic processing of polyfunctional precursor proopiomelanoc ortin (POMC) occurs in a developmentally regulated manner. We have sho wn that while PC2 mRNA is predominately expressed in the intermediate lobe in the adult, we observed an increased expression of PC2 mRNA in developing rat anterior lobe, peaking at early postnatal stages. The e xpressions of PCI and PC2 in early postnatal pituitary overlap with PO MC expression and the levels of PC1 and PC2 expression in pituitary pa rallel changes in POMC endoproteolytic processing pattern, suggesting regulation of endoprotease expression may account for differential pro cessing of proproteins in development.