Coding Region Of Exon Research Articles

CCP II : A Novel Calcitonin Carboxy Terminal Peptide is Expressed in Normal Thyroid Tissue

We have recently identified in medullary thyroid carcinoma the existence of a second calcitonin messenger, generated by a splicing between the 3' coding region of exon 4 and exon 5 of Calc I gene. It differs from the first one in its 3' coding sequence and codes for a calcitonin precursor which generates the same N terminal peptide, calcitonin and a specific 21 amino acid carboxy terminal peptide differing from Katacalcin by its 8 last amino acids. We searched for the expression of this new messenger in normal human thyroid tissue by Northern and by polymerase chain reaction techniques. This second calcitonin messenger was expressed in 4/4 normal thyroids and 4/5 medullary thyroid carcinoma tissue samples. The expression of this second messenger is apparently a common occurrence in C cells whether normal or tumoral.

Corticotropin-releasing factor upregulates expression of two truncated pro-opiomelanocortin transcripts in murine lymphocytes

Lymphocytes harbor a pro-opiomelanocortin (POMC) mRNA. In this report, a novel procedure was used to study the exonic arrangement of this transcript in lymphocytes. Poly(A) + mRNA, purified from both corticotropin-releasing factor (CRF)-treated and nontreated lymphocytes, was selectively reverse-transcribed using an antisense oligonucleotide primer complementary to the 3′ junction of the translated/nontranslated region of exon 3 of POMC. Alkaline agarose gel analysis of first-strand cDNA synthesis showed an upregulation of POMC transcripts in CRF-treated cells. This first-strand cDNA was amplified in a polymerase chain reaction (PCR) using the complementary antisense primer and selective sense primers homologous to the 5′ ends of exons 1, 2, and 3, as well as a region immediately 5′ to the ACTH/β-lipotropin coding region of exon 3 of pituitary POMC. Primers directed at exons 1 and 2 did not amplify a POMC product in nontreated control or CRF-treated cells. However, with both treated and nontreated cells, the internal exon 3 primer amplified the expected size exon 3 DNA fragment (∼ 549 bp). Interestingly, a primer directed at the 5′ end of exon 3 apparently did not amplify a POMC product in nontreated cells butdid amplify a full-size POMC exon 3 from CRF-treated cells (∼ 615 bp). However, upon reamplification of the original PCR products from nontreated cells, full-length exon 3 product was also observed. Southern gel analysis using a pituitary POMC cDNA probe showed that all of the above PCR products were POMC-related. The results of this study show that lymphocytes basally transcribe at least two POMC transcripts that are upregulated by CRF. These two transcripts lack exons 1 and 2 but contain either part or all of exon 3. The smaller exon 3 transcript was the most abundant transcript under all conditions examined.