Expression of apolipoprotein[a] and plasminogen mRNAs in cynomolgus monkey liver and extrahepatic tissues

The apolipoprotein[a] (apo[a]) and plasminogen (PLG) genes share a high degree of sequence identity, suggesting that both genes may be coordinately expressed. To address this possibility, hepatic apo[a], PLG, and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) mRNAs in 11 cynomolgus monkeys that express plasma Lp[a] over a 10-fold range (5.3-69.3 mg/dl) were measured. This analysis demonstrated a 13-fold variation in apo[a] mRNA. PLG mRNA levels ranged only 3-fold, which was similar to the deviation in G3PDH mRNA expression. Lp[a] and PLG plasma levels were also not related in the animals. To further define expression of the latter mRNAs, they were measured in liver and 13 extrahepatic tissues from 5 monkeys. Apo[a] transcript was detected for the first time in adrenal, lung, and pituitary in addition to brain and testes. PLG mRNA was detected extrahepatically only in testes while G3PDH mRNA was ubiquitously expressed. In individual animals, there was no relationship between hepatic and extrahepatic apo[a] mRNA levels suggesting tissue-dependent expression of the transcript. These results demonstrate that although the apo[a] and PLG genes are highly homologous, their mRNA expression differs markedly.