Chemotaxis in the Marine Fungus Rhizophydium littoreum

Zoospores of the marine chytrid Rhizophydium littoreum are attracted to a variety of substances common to their environment. In general, carbohydrates and polysaccharides elicited strong concentration-dependent positive responses. There was no direct correlation between all substances used as foods and those stimulating positive responses. The chemotactic activities of this organism should, however, tend to bring it toward concentrated food sources.     

Packing of the 30 nm chromatin fiber in the human metaphase chromosome

The human genetic material is packed hierarchically within the metaphase chromosome: the DNA moleculet together with histone proteins form 11 nm diameter nucleosomes, which are then ordered into the 30 nm thick chromatin fiber. Little is known about the packing of this fiber within the chromosome. We have developed a tracking algorithm with which we followed its path within a three-dimensional reconstruction of a human chromosome computed from a series of electron micrographie projections. Fiber segments were seen to form loops of 100–350 nm diameter. Our observations indicate that these loops — which themselves show no preferred orientation — are organised into regions of roughly 200 nm axial extent.     

Surface changes in chimpanzee sperm during epididymal transit

Intact chimpanzee caput and cauda epididymal sperm, sperm cell lysates, and caput and cauda epididymal fluid were radiolabeled by enzymatic iodination with lactoperoxidase and Na125 I and were compared by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Caput epididymal sperm showed nine labeled macromolecular components of 90, 64, 56, 48, 38, 31, 20, 18 and 16 Kd and cauda epididymal sperm showed eleven macromolecular components of 90, 64, 55, 47, 42, 33, 27, 18, 17, 15 and 11 Kd. Six of the components labeled on caput sperm (90, 64, 56, 48, 18 and 16 Kd) were detected in equal amounts of cauda sperm and two (38 and 20 Kd) were detected at greatly reduced labeling intensities. In the cauda epididymidis, four new components (33, 27, 17 and 11 Kd) became prominent features of the sperm surface. Analysis of labeled caput and cauda sperm cell lysates resolved components distinct from those detected on sperm surfaces. Electrophoresis of caput epididymal fluid showed five labeled components of 66, 56, 47, 41 and 37 Kd, while electrophoresis of cauda epididymal fluid showed eight labeled components of 92, 66, 56, 48, 31, 27, 24 and 11 Kd. Three components (66, 56 and 47 Kd) were present in both caput and cauda fluid, two (41 and 37 Kd) in caput fluid only, and five (92, 31, 27, 24 and 11 Kd) in cauda fluid only. Components of 37 Kd were labeled in caput fluid and on caput sperm but not on cauda sperm, whereas components of 27 Kd and 11 Kd were labeled in cauda fluid and on cauda sperm but not on caput sperm. These data show that chimpanzee sperm undergo extensive surface modifications during epididymal maturation and that some of these modifications may be related to exogenous proteins/glycoproteins in epididymal fluids.     

Morphogenic substances released by plant tissue cultures

The release of endogenous substances is a general phenomenon of plant tissue cultures, with some substances having significant developmental effects on the releasing tissues. Their systematic study was initiated with Nandina tissue cultures, and a yellow compound that accumulated in the culture medium was identified as the alkaloid, berberine. The rate of its release was related to the supplies of auxin, cytokinin, and nutrient salts. Addition of berberine \ HCl to nutrient media did not inhibit Nandina tissues, but suppressed shoot formation in Nicotiana stem segments. Growth of Nandina and Nicotiana callus, as well as rooting of Nicotiana stem segments, was promoted by alkaloid addenda.     

Gulf Stream warm core rings: phytoplankton in two fall rings of different ages

Warm core ring (WCR) 82-H was sampled in September–October(1982) as a Gulf Stream meander pinched off and became a ring.It is compared with the 3-month-old WCR 81-D, visited September–October(1981). Although the rings have different histories, their phytoplanktonassemblages share some characteristics. Using cluster analysesbased on quantitative group counts, a station from one ringoccasionally clusters most closely with a station from the otherring, showing a similar balance of organisms. The younger ringat the time of sampling, WCR 82-H, had lower diversity, fewershelf species, and greater consistency between stations, exceptfor a high level of Oscillatoria in the meander before the ringpinched off. Interaction with slope water was seen principallyat the ring margin. WCR 81-D, on the other hand, showed a greatdeal of structure, and immediate dilutions with slope waterand the Gulf Stream were apparent, with higher diversity beforeand a week after such interactions. The upper water column ofwarm core rings, although showing evidence of physical mixing,can exhibit stratification of species, even after a storm.     

Interaction of human spermatozoa with the human zona pellucida and zona-free hamster oocyte following capacitation by exposure to human cervical mucus

The functional capacity for sperm interaction with the human zona pellucida and zona-free hamster oocyte was tested after human spermatozoa were capacitated by passage through a column of human cervical mucus. The results were compared with those obtained when spermatozoa from an aliquot of the same semen sample were capacitated by the standard laboratory methods involving sequential washing by dilution and centrifugation of the semen. Washed-capacitated sperm suspensions were more successful than mucus-capacitated sperm in attaching to the zona-free hamster oocyte and in fusing with its oolemma. However, the ability of mucus-capacitated sperm to penetrate the human zona pellucida was equal to washed capacitated sperm. These experiments demonstrate an approach that may be useful in comparative studies of human sperm capacitation in vivo and in vitro.     

Radiogenic initiation of thyroid cancer: a common cellular event

A transplantation system for clonogenic cells in rat thyroid was used, which allows quantitative evaluation of both the acute cytotoxicity and the late neoplastic effects of ionizing radiation at the cellular level in vivo. We have obtained direct experimental evidence that radiogenic initiation of neoplasia in vivo is a common cellular event, and that cell number influences the expression of initiation. Ten per cent of those graft sites which had received 26 clonogens surviving 5 Gy developed carcinomas, while 4 per cent of those which received 26 unirradiated clonogens developed carcinomas. By comparison, 26 per cent of the sites that were inoculated with 411 surviving irradiated clonogens developed carcinomas while none of the 38 transplant sites that received 411 unirradiated clonogens developed carcinomas. Total tumour incidence (carcinomas plus adenomas) followed the same pattern.     

Changes in binding of a 27-kilodalton chimpanzee cauda epididymal protein glycoprotein component to chimpanzee sperm

Motility patterns of caput epididymal chimpanzee sperm, caput epididymal chimpanzee sperm incubated in vitro with chimpanzee cauda epididymal fluid, and cauda epididymal chimpanzee sperm were assessed quantitatively. Sperm recovered from the caput epididymis showed no motility, whereas sperm recovered from cauda epididymis showed progressive forward motility. After incubation in cauda fluid, approximately 25% of caput epididymal sperm showed some motile activity. Electrophoretic analysis of ¹²⁵I-labeled sperm plasma membrane preparations revealed that the surface of caput epididymal sperm, incubated in cauda fluid, was modified by the appearance of a major protein-glycoprotein surface component with an apparent molecular weight of 27 kilodaltons (kD). THis 27-kD component was not detected on caput epididymal sperm incubated in buffer or in caput fluid. However, it was present in cauda fluid and on cauda epididymal sperm. Binding to caput epididymal sperm was cell specific in that chimpanzee erythrocytes incubated in cauda fluid did not bind this 27-kD cauda fluid component. Motility patterns of ejaculated chimpanzee sperm and of ejaculated chimpanzee sperm incubated in the uterus of adult female chimpanzees also were assessed quantitatively. Ejaculated sperm showed progressive forward motility, whereas in utero incubated ejaculated sperm showed hyperactivated motility typical of capacitated sperm. Electrophoretic analysis of ¹²⁵I-labeled sperm plasma membrane preparations revealed the loss of a 27-kD component from the surface of ejaculated sperm after in utero incubation. No significant change in the ¹²⁵I-distribution pattern was detectable when ejaculated sperm were incubated in buffer. These results suggest that the lumenal fluid component, which becomes adsorbed to the surface of chimpanzee sperm during maturation in the epididymis and which is removed from the surface of mature chimpanzee sperm in the female reproductive tract, affects sperm motility.