The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.

Three experimental techniques based on automatic swept-frequency network and impedance analysers were used to measure the dielectric properties of tissue in the frequency range 10 Hz to 20 GHz. The technique used in conjunction with the impedance analyser is described. Results are given for a number of human and animal tissues, at body temperature, across the frequency range, demonstrating that good agreement was achieved between measurements using the three pieces of equipment. Moreover, the measured values fall well within the body of corresponding literature data.

The development and progression of thyroid tumors is signaled by phenotype-specific mutations of genes involved in growth control. Molecular events associated with undifferentiated thyroid cancer are not known. We examined normal, benign, and malignant thyroid tissue for structural abnormalities of the p53 tumor suppressor gene. Mutations were detected by single-strand conformation polymorphisms of PCR-amplified DNA, using primers bracketing the known hot spots on either exons 5, 6, 7, or 8. The prevalence of mutations was as follows: normal thyroid 0/6; follicular adenomas 0/31; papillary carcinomas 0/37; medullary carcinomas 0/2; follicular carcinomas 1/11; anaplastic carcinomas 5/6; thyroid carcinoma cell lines 3/4. Positive cases were confirmed by direct sequencing of the PCR products. All five anaplastic carcinoma tissues and the anaplastic carcinoma cell line ARO had G:C to A:T transitions leading to an Arg to His substitution at codon 273. In both tumors and cell lines, examples of heterozygous and homozygous p53 mutations were identified. The only thyroid carcinoma cell line in which p53 mutations were not detected in exons 5-8 had markedly decreased p53 mRNA levels, suggesting the presence of a structural abnormality of either p53 itself or of some factor controlling its expression. The presence of p53 mutations almost exclusively in poorly differentiated thyroid tumors and thyroid cancer cell lines suggests that inactivation of p53 may confer these neoplasms with aggressive properties, and further loss of differentiated function.

Thyroparathyroidectomy of rats on a diet low in calcium reduces production of 1,25-dihydroxycholecalciferol from 25-hydroxycholecalciferol to negligible levels within 40 hr, and increases production of another metabolite, called Va. Parathyroid extract, at a dose of 20 units per day, prevents these changes. When 40 units per day of parathyroid extract is given 48 hr after thyroparathyroidectomy, 1,25-dihydroxycholecalciferol production is restored almost to control levels within 36 hr. The change brought about by parathyroid extract cannot be attributed to resulting changes in serum calcium or phosphorus concentration. It appears that the parathyroid hormone serves as a tropin for production of 1,25-dihydroxycholecalciferol, the hormonal form of vitamin D responsible for calcium mobilization from intestinal contents and bone.

We used the lung epithelial cell-specific surfactant protein B (SPB) gene promoter as a model with which to investigate mechanisms involved in transcriptional control of lung-specific genes. In a previous study, we showed that the SPB promoter specifically activated expression of a linked reporter gene in the continuous H441 lung cell line and that H441 nuclear proteins specifically protected a region of this promoter from bp -111 to -73. In this study, we further show that this region is a complex binding site for thyroid transcription factor 1 (TTF-1) and hepatocyte nuclear factor 3 (HNF-3). Whereas TTF-1 bound two highly degenerate and closely spaced sites, HNF-3 proteins bound a TGT3 motif (TGTTTGT) that is also found in several liver-specific gene regulatory regions, where it appears to be a weak affinity site for HNF-3. Point mutations of these binding sites eliminated factor binding and resulted in significant decreases in transfected SPB promoter activity. In addition, we developed a cotransfection assay and showed that a family of lung-specific gene promoters that included the SPB, SPC, SPA, and Clara cell secretory protein (CCSP) gene promoters were specifically activated by cotransfected TTF-1. We conclude that TTF-1 and HNF-3 are major activators of lung-specific genes and propose that these factors are involved in a general mechanism of lung-specific gene transcription. Importantly, these data also show that common factors are involved in organ-specific gene expression along the mammalian foregut axis.

The cDNA for TTF-1, a thyroid nuclear factor that binds to the promoter of thyroid specific genes, has been cloned. The protein encoded by the cDNA shows binding properties indistinguishable from those of TTF-1 present in nuclear extracts of differentiated rat thyroid cells. The DNA binding domain of TTF-1 is a novel mammalian homeodomain that shows considerable sequence homology to the Drosophila NK-2 homeodomain. TTF-1 mRNA and corresponding binding activity are detected in thyroid and lung. The chromosomal localization of the TTF-1 gene has been determined in humans and mice and corresponds to chromosomes 14 and 12, respectively, demonstrating that the TTF-1 gene is not located within previously described clusters of homeobox-containing genes.