Troponin I is the inhibitory component of troponin, the thin filament regulatory complex in striated muscle. Separate genes encode cardiac-specific fast and slow skeletal-specific isoforms of this protein. We have previously described gene switching from the slow skeletal to the cardiac troponin I mRNA expression in developing rat heart. The purpose of this work was to characterize the expression of the different troponin isoforms in the human heart. Human cardiac and slow skeletal troponin I cDNA probes were obtained by screening an adult cardiac cDNA library and by Taq polymerase amplification of RNA from an infant's heart, respectively. We found that the cardiac troponin I isoform is tissue-specific in its expression in normal adult tissues. RNA blot analysis of cardiac ventricular RNA from infants with congenital heart disease and from an adult with cardiomyopathy revealed expression of human cardiac troponin I in all analyzed specimens. In addition, we found expression of slow skeletal troponin I mRNA and protein in infant hearts but no detectable mRNA expression in the adult heart. We conclude that troponin I isoforms are developmentally regulated in the human heart by a mechanism similar to that in the rat heart.

In vitro, pancreatic triglyceride lipase requires colipase to restore activity in the presence of inhibitors, like bile acids. Presumably, colipase performs the same function in vivo, but little data supports that notion. Other studies suggest that colipase or its proform, procolipase, may have additional functions in appetite regulation or in fat digestion during the newborn period when pancreatic triglyceride lipase is not expressed. To identify the physiological role of procolipase, we created a mouse model of procolipase deficiency. The Clps ؊/؊ mice appeared normal at birth, but unexpectedly 60% died within the first 2 weeks of life. The survivors had fat malabsorption as newborns and as adults, but only when fed a high fat diet. On a low fat diet, the Clps ؊/؊ mice did not have steatorrhea. The Clps ؊/؊ pups had impaired weight gain and weighed 30% less than Clps ؉/؉ or Clps ؉/؊ littermates. After weaning, the Clps ؊/؊ mice had normal rate of weight gain, but they maintained a reduced body weight compared with normal littermates even on a low fat diet. Despite the reduced body weight, the Clps ؊/؊ mice had a normal body temperature. To maintain their weight gain in the presence of steatorrhea, the Clps ؊/؊ mice had hyperphagia on a high fat diet. Clps ؊/؊ mice had normal intake on a low fat diet. We conclude that, in addition to its critical role in fat digestion, procolipase has essential functions in postnatal development and in regulating body weight set point.

We report the complete molecular organization of the Dopa decarboxylase gene cluster. Mutagenesis screens recovered 77 new Df(2L)TW130 recessive lethal mutations. These new alleles combined with 263 previously isolated mutations in the cluster to define 18 essential genes. In addition, seven new deficiencies were isolated and characterized. Deficiency mapping, restriction fragment length polymorphism (RFLP) analysis and P-element-mediated germline transformation experiments determined the gene order for all 18 loci. Genomic and cDNA restriction endonuclease mapping, Northern blot analysis and DNA sequencing provided information on exact gene location, mRNA size and transcriptional direction for most of these loci. In addition, this analysis identified two transcription units that had not previously been identified by extensive mutagenesis screening. Most of the loci are contained within two dense subclusters. We discuss the effectiveness of mutagens and strategies used in our screens, the variable mutability of loci within the genome of Drosophila melanogaster, the cytological and molecular organization of the Ddc gene cluster, the validity of the one band-one gene hypothesis and a possible purpose for the clustering of genes in the Ddc region.

The pancreas makes two pancreatic proteins [pancreatic lipase-related protein-1 (PLRP-1) and PLRP-2] with marked homology to pancreatic lipase (PL). To determine if a pancreatic acinar cell line, AR42J, also expresses PLRP-1 and PLRP-2, we examined the cells for the presence of PL, PLRP-1, and PLRP-2. RNA blot analysis with specific probes and immunoblot analysis with antipeptide antibodies demonstrated the presence of mRNA and protein for all three homologues in AR42J cells. Additionally, we showed that dexamethasone decreased PLRP-1 mRNA levels twofold and increased PLRP-2 mRNA 20-fold but had little effect on PL or colipase mRNA. Extracellular PLRP-2 protein levels increased threefold, and intracellular PLRP-2 protein levels increased about fourfold. The characteristics of the dexamethasone-induced increase in PLRP-2 mRNA, a rapid change requiring new protein synthesis independent of mRNA turnover, suggested that dexamethasone regulated transcription. We conclude that AR42J cells synthesize and secrete PL, PLRP-1, and PLRP-2 and that dexamethasone discoordinately regulates the expression of the three genes.