Vimentin expression in oocytes, eggs and early embryos of Xenopus laevis

Immunocytochemical studies using a monoclonal anti-porcine vimentin antibody reveal a well-organized pattern of staining in Xenopus laevis oocytes, eggs and early embryos. The positions of Xenopus vimentin and desmin in two-dimensional (2D) polyacrylamide gels were first established by immunoblotting of muscle Triton extracts with anti-intermediate filament antibodies (anti-IFA), which cross-react with all intermediate filament proteins (IFPs). The anti-porcine vimentin reacts with vimentin and desmin in muscle 2D immunoblots, but only reacts with one polypeptide in oocyte blots in the position predicted for vimentin (Mr 55 x 10(3), pI 5.6). Using an anti-sense probe derived from a Xenopus vimentin genomic clone in RNase protection assays, we show that expression of vimentin begins in previtellogenic oocytes. The level of expression remains constant throughout oogenesis and in unfertilized eggs. These data suggest that vimentin is expressed in oocytes and eggs. Most interestingly, the immunocytochemical results also show that vimentin is present in the germ plasma of oocytes, eggs and early embryos. It is therefore possible that vimentin has an important role in the formation or behaviour of early germ line cells.     

Some Umbelliferae of the Andean paramos of South America

Two Colombian species described earlier by the authors underPrionosciadium, and a hitherto unnamed collection from the same country are systematically compared with North AmericanPrionosciadium and the monotypic generaCotopaxia (Ecuador) andPerissocoeleum (Colombia). Habit, foliage, inflorescence, fruit, and distribution all suggest that the páramo species exhibit considerable unity ifCotopaxia is excluded. It is indicated also that the genusPrionosciadium has been attributed to South America incorrectly. Despite the somewhat discordant evidence obtained from pollen morphology, it is concluded that the most feasible disposition of the four Colombian plants is to unite them underPerissocoeleum.     

Magic,myth and medicine

Carrots, celery, caraway and cumin and their relatives in the Apiaceae (Umbelliferae) have a long history of human use dating from our earliest written records. A large body of folklore has accumulated on their magical and mythical curative properties. Many of the early uses have persisted as part of 20th century folklore, sometimes supplementary to modern medicine. Studies largely during the last half of this century have provided the chemical bases for some of the ancient cures.     

Utilization of Xylan by Two Species of Human Colonic Bacteroides

During growth of two strains of human colonic Bacteroides on xylan, several oligomers, the smallest of which was xylobiose, were released into the medium.     

Effect of an extract of nereis virens on mammalian spermatozoa

Epididymal sperm of the mouse, rat, and guinea pig and ejaculated sperm of rabbits are cleaved at the head-tail junction by an extract of Nereis virens. Annelids are extracted with water and the extract is purified by ion exchange chromatography. Electron microscopy shows that the extract acts on the filaments connecting the capitulum of the tail with the basal plate lining the nuclear envelope. Following detachment, the basal plate remains with the head. The extract contains proteases as indicated by hydrolysis of tosyl arginine methyl ester (TAME), benzoyl arginine ethyl ester (BAEE), and Azocoll, a general protease substrate. The hydrolysis of TAME is inhibited by tosyl lysine chloromethyl ketone (TLCK), a trypsin inhibitor, but TLCK does not prevent head-tail separation by the Nereis extract. Similarly tosyl phenylalanine chloromethyl ketone (TPCK), a chymotrypsin inhibitor, and phosphoramidon and leucyltryptophan, both thermolysin and acrolysin inhibitors — singly or in combination — do not prevent hydrolysis of Azocoll. Head-tail separation activity of the extract was inhibited by dithiothreitol, which reduces disulfide bonds, and phenylmethyl sulfonyl fluoride, an inhibitor of serine proteases. These results indicate that the extract is a mixture of proteases, one being a serine protease similar to trypsin. Digestion of the connecting filaments with the pure proteases, trypsin and Staphylococcus aureus V8 protease, has yielded the following information on the proteins of the filaments. The accessibility of arginine and/or lysine peptide bonds to enzyme action is highest in rat sperm filaments, whereas those in the filaments of mouse, rabbit, and guinea pig sperm are less accessible than in the rat. Another possibility is that the total content of arginine and/or lysine varies between the species. The most dramatic difference is the enzymatic action on glutamyl peptide bonds of the filaments, the order being: mouse 〉 rat 〉 rabbit, with guinea pig sperm filaments completely resistant over the time course of the experiment.     

The rise and fall of pineal N-acetyltransferase in vitro: Neural regulation in the developing rat

In rats, the pineal gland has a rhythm in the activity of the enzyme, N-acetyltransferase (NAT), which is thought responsible for daily cycles of melatonin synthesis. Neonatal rat pineal glands, but not those of adult rats, have a single cycle that is observed in vitro during the first day of organ culture. The neural regulation of the cycle was investigated using neonatal rats with adult rats used for comparison. Prior treatment of rat pups with constant light did not abolish the cycle in vitro though it did abolish the in vivo rhythm. Removal of the superior cervical ganglia did not abolish the in vivo rhythm that was measured the first day after surgery, but ablation of the ganglia did abolish the rhythm if several days or more elapsed after surgery. Extirpation of the superior cervical ganglia abolished the in vitro NAT cycle in pup pineal glands as did the pharmacological equivalent, injection of 6-hydroxydopamine. Propranolol, a beta blocking agent, prevented the occurrence of the cycle in vitro.     

Evidence for substrate guidance of primordial germ cells

Primordial germ cells (PGCs) have been removed from their normal migratory route in early embryos of Xenopus laevis, and their behaviour studied in vitro. They adhere to, and move over the upper surface of, layers of outgrowing cells from expiants of adult Xenopus mesentery. They move by the extrusion of single filopodia, elongation, forward streaming of the yolky cytoplasm and retraction of their trailing ends. When the underlying cells are polarized in one direction only, PGCs always elongate and move along the same direction. Furthermore, when PGCs elongate and move over less obviously polarized cells, they always do so in the direction of ‘stress fibres’ (actin bundles) in the underlying cells. A substrate-guidance hypothesis for PGC migration is only tenable if there is some orientation in their natural substrate in vivo. Using the scanning electron microscope, we demonstrate that the coelpmic lining cells, beneath which PGCs migrate up the dorsal mesentery of the gut, are orientated in the direction of travel. Furthermore, this orientation changes at the time of gonadal ridge formation. This raises the intriguing possibility that PGCs are guided for at least part of their migration in Xenopus laevis embryos by a substrate-guidance mechanism.