Fluorescence in situ hybridization (FISH) and digital imaging microscopy were modified to allow detection of single RNA molecules. Oligodeoxynucleotide probes were synthesized with five fluorochromes per molecule, and the light emitted by a single probe was calibrated. Points of light in exhaustively deconvolved images of hybridized cells gave fluorescent intensities and distances between probes consistent with single messenger RNA molecules. Analysis of beta-actin transcription sites after serum induction revealed synchronous and cyclical transcription from single genes. The rates of transcription initiation and termination and messenger RNA processing could be determined by positioning probes along the transcription unit. This approach extends the power of FISH to yield quantitative molecular information on a single cell.

The transport of mRNAs into developing dendrites and axons may be a basic mechanism to localize cytoskeletal proteins to growth cones and influence microfilament organization. Using isoform-specific antibodies and probes for in situ hybridization, we observed distinct localization patterns for beta- and gamma-actin within cultured cerebrocortical neurons. beta-Actin protein was highly enriched within growth cones and filopodia, in contrast to gamma-actin protein, which was distributed uniformly throughout the cell. beta-Actin protein also was shown to be peripherally localized after transfection of beta-actin cDNA bearing an epitope tag. beta-Actin mRNAs were localized more frequently to neuronal processes and growth cones, unlike gamma-actin mRNAs, which were restricted to the cell body. The rapid localization of beta-actin mRNA, but not gamma-actin mRNA, into processes and growth cones could be induced by dibutyryl cAMP treatment. Using high-resolution in situ hybridization and image-processing methods, we showed that the distribution of beta-actin mRNA within growth cones was statistically nonrandom and demonstrated an association with microtubules. beta-Actin mRNAs were detected within minor neurites, axonal processes, and growth cones in the form of spatially distinct granules that colocalized with translational components. Ultrastructural analysis revealed polyribosomes within growth cones that colocalized with cytoskeletal filaments. The transport of beta-actin mRNA into developing neurites may be a sequence-specific mechanism to synthesize cytoskeletal proteins directly within processes and growth cones and would provide an additional means to deliver cytoskeletal proteins over long distances.

Maintenance of telomere length is predicted to be essential for bypass of senescence and crisis checkpoints in cancer cells. The impact of telomere dysfunction on tumorigenesis was assessed in successive generations of mice doubly null for the telomerase RNA (mTR) and the INK4a tumor suppressor genes. Significant reductions in tumor formation in vivo and oncogenic potential in vitro were observed in late generations of telomerase deficiency, coincident with severe telomere shortening and associated dysfunction. Reintroduction of mTR into cells significantly restored the oncogenic potential, indicating telomerase activation is a cooperating event in the malignant transformation of cells containing critically short telomeres. The results described here demonstrate that loss of telomere function in a cancer-prone mouse model possessing intact DNA damage responses impairs, but does not prevent, tumor formation.

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We studied the dynamics of androgen, estrogen, and cortisol (F) production, metabolism, and protein binding in cynomolgus monkeys (M. fascicularis) to provide baseline data and to compare these parameters with those obtained in other primates. Constant infusions of 3H-labeled androgens, 14C-labeled estrogens, and [3H]F were administered to 11 male cynomolgus monkeys (M. fascicularis) for 3.5 h. Blood samples were obtained from a peripheral vein during the infusion, and all urine was collected for 96 h. In each of 3 monkeys, a catheter was inserted into the hepatic vein, and during the infusions blood samples were obtained from the hepatic and peripheral veins and the femoral artery. All blood and urine samples were analyzed for radioactivity as testosterone (T), androstenedione (A), dihydrotestosterone (DHT), estradiol (E2), and estrone (E1). When indicated, blood samples were also analyzed for radioactivity as F. Blood samples taken before the infusions were analyzed for endogenous T, A, DHT, E1, E2, and F concentrations; percent free T, free E2, and free F; and sex hormone-binding globulin and F-binding globulin capacities. The mean +/- SE MCRs for T, A, E2, E1, and F were 44 +/- 4, 407 +/- 40, 175 +/- 17, 315 +/- 28, and 57 +/- 6 liters/day, respectively. The mean blood production rates were 128 +/- 19, 91 +/- 14, 3.3 +/- 0.5, and 9.2 +/- 1.1 micrograms/day and 13.4 +/- 1.9 mg/day for T, A, E2, E1, and F, respectively. The aromatization of androgens was 1.30 +/- 0.10% for A to E1 and 0.28 +/- 0.03% for T to E2. The percent free F (4.34 +/- 0.42%) was greater than the percent free T (1.73 +/- 0.16%) or free E2 (2.75 +/- 0.22%), and the concentration of F-binding globulin was greater than that of sex hormone-binding globulin (227 +/- 35 vs. 60 +/- 7 nM). In the three monkeys who had hepatic venous catheterization, the mean extraction, across the splanchnic bed of T was 32 +/- 3%, that of E was 62 +/- 2%, and that of cortisol was 12 +/- 5%. Across peripheral tissues (leg) the mean extractions were 13 +/- 1%, 18 +/- 1%, and 6 +/- 4%, respectively. In general, the dynamics of androgen, estrogen, and F production and metabolism are similar in male cynomolgus and rhesus monkeys and in man. The similarity is especially close for peripheral aromatization despite differences in adipose tissue content between man and nonhuman primates.

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We studied, in four normal men, the metabolism of 2-methoxyestrone (2-MeOE1) using pulse injections of either [3H]2MeOE1 (two men) or [14C]methoxy-2-MeOE1 plus [3H]2-MeOE1 (two men) by analysis of blood samples drawn at increasing time intervals after the pulse and of urine collected for 5 days. The disappearance from the blood of radioactivity as 2-MeOE1 could be characterized as a function that was the sum of three exponentials. The mean +/- SE value for the initial volume of distribution was 32 +/- 9 liters, and the mean MCR was 2470 +/- 770 liters/day. The disappearance of total 3H radioactivity from the blood was considerably slower, with a mean MCR of 290 +/- 30 liters/day, indicating the presence of a slowly turning over pool of 2-MeOE1 metabolites, probably including the 2-MeOE1 3-sulfate conjugate. The disappearance of total 14C radioactivity was slower than that of total 3H, indicating considerable demethylation of 2-MeOE1 with a very slow excretion of 14C from the released methyl group. In none of the subjects could we find in the blood radioactivity as unconjugated [3H]2-hydroxyestrone ( [3H]2-OHE1). However, examination of the urine indicated that considerable demethylation of [3H]2-MeOE1 had occurred. At least 64% of the urinary 3H-containing metabolites from the mixed dose had lost the 14C-bearing methoxylcarbon atom. The fractionated metabolites were qualitatively and quantitatively similar to those found earlier for [3H]2-OHE1. We conclude that 2-MeOE1, which of itself has little biological activity, can act as a pool of potentially active 2-OHE1 in the tissues.

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