A rat thyroglobulin promoter fragment, capable of directing thyroid‐specific transcription, binds at least three different factors, TTF‐1, TTF‐2 and UFA, which are all present in nuclear extracts of the differentiated rat thyroid cell line FRTL‐5. TTF‐1 and TTF‐2 are FRTL‐5 specific, as demonstrated by their absence in nuclear extracts prepared from cell lines that do not express any thyroid‐differentiated function, while UFA is present in all cell lines tested. TTF‐1 has been extensively purified. It binds to the rat thyroglobulin promoter at three different sites which share sequence homology. Mutations in two of the three sites decrease both binding of TTF‐1 in vitro and promoter function in vivo. This suggests that the tissue‐specific expression of the thyroglobulin genes is mediated, at least in part, by the presence of a transcription factor exclusively in thyroid cells.

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Thyroid-specific expression of the rat thyroglobulin gene is mediated by transcriptional control. Sufficient DNA sequence information to confer thyroid-specific expression to a heterologous gene is contained between positions -168 and + 39. DNA-binding studies have demonstrated that this region interacts with two thyroidspecific factors (TTF-1 and TTF-2), and a ubiquitous factor (UFA). Here we have characterized three elements within the promoter, A, K, and C, which are important for promoter activity in thyroid cells. We have shown by mutational analysis that the interaction of TTF-1 with the A and C regions, UFA with the A region, and TTF-2 with the K region are required for full promoter activity. The complex interactions in the A region can be replaced by the substitution of the UFA/TTF-1-binding site with a high-affinity TTF-1 binding site. There is a correlation between the presence of TTF-1 and TTF-2 DNA-binding activities and the expression of thyroglobulin, which implies that the mechanism restricting thyroglobulin expression to thyroid cells is mediated through the control of the expression, or the activity, of TTF-1 and TTF-2.The follicular cells of the thyroid gland are required for the production and controlled release of the thyroid hormones, 3',3,5-triiodothyronine and thyroxin. There are at least four functions which are good markers for the differentiated status of the follicular cells : expression of thyroglobulin, thyroid peroxid,ase, a Na+/l-symport, and the thyroid-stimulating hormone (TSH) receptor [l, 21. Of these functions, only the genes encoding thyroglobulin and thyroid peroxidase have been cloned [3 -61. Both thyroglobulin and thyroid peroxidase mRNA are only detectable in thyroid tissues. The 5' flanking DNA from the rat thyroglobulin gene is able to confer thyroid-specific expression to a heterologous gene, which shows that the thyroid-specific expression of the gene is mediated, at least in part, by transcriptional control [7]. The shortest region of the DNA that can act as a thyroid-specific promoter is located between nucleotides -168 and + 39 [7]. This sequence is thought to interact with the transcriptional apparatus to mediate the expression of thyroglobulin in thyroid cells. We have investigated the interaction between nuclear factors from thyroid and non-thyroid cells with the thyroglobulin promoter [S]. A DNA sequence, which is repeated three times, specifically interacts with a thyroid-specific DNA-binding activity, TTF-1. A second thyroid-specific DNA-binding activity, TTF-2, and an ubiquitous DNA-bindCorrespondence to R. Di Lauro, EMBL, Meyerhof Strasse 1, W-6900 Heidelberg, Federal Republic of GermanyAbbreviations. TTF-1; thyroid transcription factor 1 ; TTF-2, thyroid transcription factor 2; UFA, ubiquitous factor A; RSV, Rous sarcoma virus; CAT, chloramphenichol acetyltransferase; TSH, thyroid-stimulating hormone.Enzymes. Restriction endonucleases (EC 3.1.21.4); DNA polymerase I (EC 2.7.7.7); chloramphenicol acetyltransferase (EC 2.3.1.28); thymidine kinase (EC 2.7.1....

Myotonic dystrophy (DM) is a multisystemic disease caused by the expansion of a CTG repeat, located in the 3'-untranslated region of the DMPK gene. The number of CTG repeats broadly correlates with the overall severity of the disease. However, correlations between CTG repeat number and presence/absence or severity of individual clinical manifestations in the same patients are yet scarce. In this study the number of CTG repeats detected in blood cells of 24 DM subjects was correlated with the severity of single clinical manifestations. The presence/absence of muscular atrophy, respiratory insufficiency, cardiac abnormalities, diabetes, cataract, sleep disorders, sterility or hypogonadism is not related to the number of CTG repeats. Muscular atrophy and respiratory insufficiency are present with the highest frequency, occurring in 96 and 92% of the cases, respectively. A significant correlation was found with age of onset (r = -0.57, p<0.01), muscular disability (r = 0.46, p<0.05), intellective quotient (r = -0.58, p<0.01) and short-term memory (r= -0.59, p<0.01). Therefore, the CTG repeat number has a predictive value only in the case of some clinical manifestations, this suggesting that pathogenetic mechanisms of DM may differ depending on the tissue.

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