Anucleolate frog embryos contain ribosomal DNA sequences and a nucleolar antigen

Previous studies of Xenopus laevis embryos homozygous for the nucleolar deletion mutation have concluded that these embryos contain few, if any, copies of the genes for the 18 S and 28 S ribosomal RNAs. Using hybridization to restriction endonuclease digests of DNA it is found, in fact, that a small amount of ribosomal DNA is still present in such embryos. The ribosomal DNA in these embryos appears to include a few normal repeats together with a variety of unusual fragments containing either spacer or gene sequences. An antibody found in the serum of a scleroderma patient reacts with an antigen localized in the nucleoli of wild-type embryos. In anucleolate embryos this antigen is found in the so-called pseudonucleoli and in many small bodies in the nuclei.     

Comparison of serum oestrogen concentrations in post-menopausal women taking oestrone sulphate and oestradiol.

Mean serum concentrations of oestradiol-17beta, oestrone, and oestrone sulphate in postmenopausal women were the same when measured up to six hours after treatment with either piperazine oestrone sulphate 1.5 mg or oestradiol valerate 2 mg. Maximum concentrations of oestradiol were less than those of oestrone, but oestrone sulphate reached concentrations about 30 times higher than those of oestrone. The rapid conversion of oestradiol valerate to oestrone and oestrone sulphate does not support the suggestion that in menopausal women oestradiol is less likely to be associated with a risk of endometrial carcinoma than oestrone sulphate, since the two preparations appear to become identical after ingestion.     

The synthesis of radioactive 3-methylthiopropionate and other alkylthio fatty acids.

Aprocedure is described for the synthesis of radioactive 3-methylthiopropionate, a recently isolated metabolite of mammalian methionine metabolism. The method is a two-step synthesis whereby correspondingly labeled methionine is degraded by ninhydrin to 3-methylthiopropionaldehyde and then specifically oxidized to 3-methylthiopropionate without oxidation of the sulfur atom by the yeast enzyme, aldehyde dehydrogenase. Radiochemical purity of the isolated product was established by paper, thin-layer, and gas-liquid chromatography. This procedure is economical and readily applicable to the synthesis of other alkylthio fatty acids for the study of S-methylcysteine and ethionine metabolism and probably for the synthesis of radioactive intermediates of branched chain amino acids.     

The purine nucleotide cycle in the regulation of ammoniagenesis during induction and cessation of chronic acidosis in the rat kidney.

The effect of chronic acid feeding and its subsequent withdrawal was determined on the amounts of the metabolic intermediates and enzymic activities of the purine nucleotide cycle. Sprague-Dawley rats were given 1.5% (w/v) NH4Cl in their drinking water for 5 days. The renal excretion of NH3 rose 70-fold and the rats developed acidosis. The amount of renal IMP rose from a control value of 4.5 +/- 2.2 to 20.4 +/- 3.7nmol/g of kidney after 48h of acid feeding (P less than 0.001) and fell to normal within 48h of the recovery. Adenylosuccinate concentrations fell from a control value of 4.5 +/- 0.9nmol/g of kidney to 1.2 +/- 0.3nmol/g (P less than 0.005) by day 5 of acidosis and continued to fall to undetectable values by 48h after recovery. The amount of AMP remained constant through the acid-feeding and the recovery periods. The activity of adenylosuccinate synthetase, the rate-limiting enzyme of the purine nucleotide cycle, paralleled the rise and fall in NH3 excretion. The activities of phosphate-dependent glutaminase and glutamate dehydrogenase were elevated during the acid-feeding and the recovery period. Thus changes in the purine nucleotide cycle correlate with changes in NH3 excretion to a more parallel degree than does the activity of glutaminase or glutamate dehydrogenase.     

Lack of impact of undergraduate genetic courses on the teaching of medical genetics.

The impact of undergraduate genetic courses on the academic performance of first-year medical students in the medical genetics course at the University of Pittsburgh School of Medicine was evaluated over a period of 9 years. Comparisons were made between medical students who had taken a formal undergraduate course in genetics and those who had not. Little if any differences were found in the academic performance in the medical genetics course between these two groups of students. Perhaps the design of undergraduate courses in genetics should be re-evaluated to give more depth to the medical student's preparation for appreciating the significance of genetics in normal and abnormal human variation.     

Peopling of the Americas: paleobiological evidence.

A subjective and bivariate analysis of 8500-10,000-year-old human fossil remains from North America substantiates that the fossils' closest affinities are with Asian populations. Within North American prehistoric Indian populations, increasing brachycephalization and the possible development of a larger, broader face are two structural trends that can be identified. In those respects where Paleo-Indian specimens differ from modern northern Asians and North American Indians, they tend to resemble southern Asian and European populations. These assessments generally support the inference that populations entered the New World relatively recently but before the modern northern Asian and North American features were fully developed. Based on the data examined, no date can be specified for time of entrance of the first populations, nor can the number of founding populations be discerned.     

Sporogonic development of Leucocytozoon smithi.

The sporogonic development of Leucocytozoon smithi in its black fly vector was studied by light and electron microscopy and was compared with that of other haemosporidians. Within 18 to 24 h after ingestion of gametocytes by black flies, ookinetes passing through the midgut epithelium were observed. Intracellular migration of ookinetes resulted in the apparent disruption and degeneration of host cells. Intercellular migration also occurred as was evidenced by the presence of ookinetes between midgut cells. Transformation of ookinete to spherical oocyst occurred extracellularly in three different sites. Although most oocysts were found between the host cell basal membrane and the basal lamina, large numbers also were found attached to the external surface of the basal lamina, projecting into the hemocoel. Ectopic development of oocysts in the midgut epithelium between cells was observed much less frequently than development on the basal side of the midgut. The oocyst wall of dense granules, believed to be of parasite origin, was distinguishable from the basal lamina of the host's midgut epithelium. As in other Leucocytozoidae, the cytoplasm of the oocyst differentiated into a single sporoblastoid from which 30-50 sporozoites were formed. Beginning on the third day post infection, elongation of segregated dense sporoblastoid material associated with pellicle thickening led to the formation of the finger-like sporozoite buds which projected into the oocyst cavity. Sporozoites within mature oocysts and salivary glands were structurally similar to sporozoites as described for other haemosporidians.     

Chemoprevention clinical trials.

As part of a program to develop drugs which will delay or prevent cancer in humans, the Chemoprevention Branch, National Cancer Institute, National Institutes of Health, is sponsoring 12 Phase I and 22 Phase II and III clinical trials. Three agent classes are significantly advanced in the trials. These are the retinoids, including 13-cis-retinoic acid, retinol, and 4-hydroxyphenylretinamide (nine studies), beta-carotene (seven studies), and calcium compounds (three studies). In addition, six promising new compounds are in Phase I or Phase II trials. These are: piroxicam, ibuprofen, oltipraz (a dithiolthione), difluoromethylornithine, glycyrrhetinic acid, and N-acetylcysteine. Key concepts related to the development of cancer chemopreventive agents are (1) the need for long-term administration, (2) the need for oral route of administration, (3) the matching of toxic side effects to degree of cancer risk.     

Cysteine sulfinic acid decarboxylase activity in response to thyroid hormone administration in rats

The modulation of hepatic and renal cysteine sulfinic acid decarboxylase (EC 4.1.1.29) activities by triiodothyronine (T3) was studied in a series of experiments. In a dose--response study, hepatic cysteine sulfinic acid decarboxylase activity (CSAD) was depressed by 65% and renal activity was increased threefold in rats injected with 100 micrograms T3/100 g body wt for 7 days when compared to rats injected with 0.3 micrograms T3/100 g body wt. Western blot analysis indicated that these changes in CSAD activity were due to changes in the quantity of CSAD protein. Changes in hepatic and renal activities were not evident until 24 h after T3 administration. In response to T3 clearance, hepatic and renal CSAD activities approached euthyroid values 4-7 days after cessation of T3 injections although serum T3 concentrations were no different from euthyroid values 48 h after T3 injections were stopped. These data indicate that thyroid hormone effects persist after T3 clearance. The response of CSAD to thyroid status may be related to its role in taurine biosynthesis.