Carnitine octanoyltransferase (COT) transports medium-chain fatty acids through the peroxisome. During isolation of a COT clone from a rat liver library, a cDNA in which exon 2 was repeated, was characterized. Reverse transcription-PCR amplifications of total RNAs from rat liver showed a three-band pattern. Sequencing of the fragments revealed that, in addition to the canonical exon organization, previously reported [Choi, S. J. et al. (1995) Biochim. Biophys. Acta 1264, 215-222], there were two other forms in which exon 2 or exons 2 and 3 were repeated. The possibility of this exonic repetition in the COT gene was ruled out by genomic Southern blot. To study the gene expression, we analyzed RNA transcripts by Northern blot after RNase H digestion of total RNA. Three different transcripts were observed. Splicing experiments also were carried out in vitro with different constructs that contain exon 2 plus the 5 or the 3 adjacent intron sequences. Our results indicate that accurate joining of two exons 2 occurs by a trans-splicing mechanism, confirming the potential of these structures for this process in nature. The trans-splicing can be explained by the presence of three exon-enhancer sequences in exon 2. Analysis by Western blot of the COT proteins by using specific antibodies showed that two proteins corresponding to the expected M r are present in rat peroxisomes. This is the first time that a natural trans-splicing reaction has been demonstrated in mammalian cells.In trans-splicing, two pre-mRNAs are processed to produce a mature transcript that contains exons from both precursors. This process is believed to proceed through two trans-esterification steps that result in the linking of the two exons by a normal 3Ј-5Ј phosphodiester bond. This process has been described mostly in trypanosoma, nematodes, plant͞algal chloroplasts, and plant mitochondria (1).Trans-splicing of artificial pre-mRNAs in mammalian cells in vitro has been reported but with some limitations (2-5). In addition, spliced leader RNAs from nematodes or from Simian virus 40 can be accurately trans-spliced in transfected COS cells, which reveals functional conservation in the splicing machinery between lower eukaryotes and mammals and demonstrated the potential for trans-splicing in mammalian cells (6). Studies in vitro also have shown that a synthetic pre-mRNA substrate containing an exon and a 5Ј donor splice site can be efficiently trans-spliced to another synthetic pre-mRNA (3Ј trans-splicing substrate) if this contains either exonic enhancers or a downstream 5Ј splice site (7-8). Several examples of possible natural trans-splicing in mammalian cells have been reported (9-12), but none of these trans-splicing have been demonstrated in vitro.During our current investigation on the carnitine octanoyltransferase (COT) gene, that encodes for an enzyme, which transports medium-chain fatty acids through the peroxisome, we isolated a cDNA COT clone, which had exon 2 repeated. We report here that the pre-mRNA of COT from rat liver produces...

Malnutrition is a common cause of secondary immune deficiency and has been linked to an increased susceptibility to infection in humans. Malnutrition specifically affects T-cell-mediated immune responses. The aim of this study was to assess in lymphocytes from malnourished children the expression levels of IL-12, IL-18 and IL-21, molecules that induce the differentiation of T cells related to the immunological cellular response (Th1 response) and the production of cytokines related to the immunological cellular response (Th1 cytokines). We found that the expression levels of IL-12, IL-18 and IL-21 were significantly diminished in malnourished children compared to well-nourished children and were coincident with lower plasmatic levels of IL-2 and IFN-γ (Th1 cytokines). In this study, we show for the first time that the gene expression and intracellular production of cytokines responsible for Th1 cell differentiation (IL-12, IL-18 and IL-21) are diminished in malnourished children. As expected, this finding was related to lower plasmatic levels of IL-2 and IFN-γ. The decreased expression of Th1 cytokines observed in this study may contribute to the deterioration of the immunological Type 1 (cellular) response. We hypothesize that the decreased production of IL-12, IL-18 and IL-21 in malnourished children contributes to their inability to eradicate infections.

In conclusion, the results suggest that alterations in the balance of type 1/type 2 immune responses exist in malnourished children, and this could be the reason that the immunological system of the malnourished children is incapable of eradicating infections.

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