Rapid separation of low molecular weight solutes from liposomes without dilution

Liposomes can be separated from low molecular weight solutes on minicolumns of Sephadex G-50 made from the barrels of 1- or 5-ml plastic syringes. Excess fluid is first removed from the Sephadex beads by centrifugation and a mixture of liposomal entrapped and free solute is applied to the column bed. The centrifugation is repeated forcing the liposomal material through the column into a test tube while the free solute is quantitatively retained in the Sephadex. The procedure is applicable to a variety of solutes and 92 to 100% recovery is achieved for both charged and neutral liposomes. This technique has advantages over other methods for separating extraliposomal solutes from liposomes. Numerous samples can be processed simultaneously within minutes with no dilution of the liposomal preparation. Nonentrapped solute within the Sephadex can be easily recovered in a small volume of water or buffer.     

Cytogenetics of the parthenogenetic grasshopper Warramaba (formerly Moraba) virgo and its bisexual relatives

Hybrids of both sexes were obtained from the reciprocal crosses, carried out in the laboratory, between the species believed to have given rise, by hybridization some thousands of years ago, to the parthenogenetic species W. virgo. All males with a Y-chromosome derived from P196 died before reaching the adult stage, but two males from the reciprocal cross (i.e., with a Y from P169) survived up to the adult stage. Their testes were small but normal in structure and histology. At the first meiotic division almost all the chromosomes were univalents, 0–2 bivalents being formed. Some chiasmata between non-homologous chromosomes were present. Segregation at first anaphase is irregular so that sperms with 3–15 chromosomes are formed. Such hybrids appear to be entirely sterile.     

Chromatin structure visualization by immunoelectron microscopy

Antibodies elicited in rabbits by chromatin and by purified histone H2B have been used to study the structure of chromatin by immunoelectron microscopy. Chromatin spread on grids reveals a structure of closely packed spherical particles with an average diameter of 104 Å, arranged either in clusters or in linear arrays of beads, some of which have a supercoil-like arrangement. No DNA strings connecting the beads could be observed. Upon antibody binding, the diameter of the particles increases up to 300 Å. This size is compatible with a model where one layer of gamma globulin molecules 110 Å long encircles a sphere of chromatin 100 Å in diameter. The presence of rabbit gamma globulins on the enlarged beads has been verified by the addition of ferritin-labeled goat anti-rabbit gamma globulins. Anti-chromatin sera which react with nonhistone proteins but not with free histones or DNA react with more than 95% of the beads; this suggests that most of the beads contain nonhistone proteins. Since the number of nonhistone proteins is large, it is improbable that each sphere contains a full complement of these proteins. We therefore suggest that the various chromatin spheres contain different types of nonhistone proteins. About 90% of the chromatin spheres reacted with antibodies to histone H2B, suggesting that most of the chromatin beads contain this type of histone.     

Lymphoma induced by herpesvirus: Resistance associated with a major histocompatibility gene

Studies with crosses of inbred chicken lines demonstrate that resistance to Marek's disease, a herpesvirus-induced lymphoma of chickens, is associated with an allele (B ²¹) of the major histocompatibility locus (theB locus). TheB ²¹ allele is thus the first genetic marker for resistance to herpesvirus-induced neoplastic disease, and our studies suggest the means whereby similar associations might be found in man.     

Amylase polymorphism: studies of sera and duodenal aspirates in normal individuals and in cystic fibrosis.

Prior genetic studies of the human pancreatic amylase (Amy2) locus have been directed principally to the electrophoretic analysis of serum and urine, on the assumption that these fluids receive negligible contributions from the salivary (Amy 1) locus. In support of that assumption was the observation that the isozyme bands were lacking in patients with cystic fibrosis and in a postpancreatectomy patient. We have examined the sera of 97 patients having cystic fibrosis and find normal levels of serum amylase. On electrophoresis, three-quarters of the cystic fibrosis patients have a pattern (F-pattern) not observed in normal sera. The pattern is characterized by the absence of Pa 1. Comparative electrophoresis and mixing experiments indicate that the F-pattern is of salivary origin and is unmasked in cystic fibrosis by the absence of a pancreatic contribution. The normal serum pattern is considered to be an admixture of salivary and pancreatic amylase. On the assumption that duodenal fluids might more closely reflect the pancreatic (Amy 2) locus, electrophoretic studies were performed on 148 normal individuals and 37 individuals with cystic fibrosis. Electrophoretic phenotypes in duodenal aspirates are more complex than previously reported in studies of urine and serum; presumably because of the higher concentrations of amylase in the aspirates. Comparative electrophoresis and mixing experiments indicate that the phenotypes observed in duodenal aspirates also reflect admixture of pancreatic and salivary amylase. This recognition of pancreatic and salivary admixture in sera fortunately does not alter our prior understanding of the genetics of the Amy 2 polymorphism. The extensive studies which led to the delineation of the Amy 2 polymorphism were essentially based on the presence or absence of a variant band which proves now to be outside the zone of admixture.     

Cytotoxic macrophages: a rapid nonspecific response to viral infection.

In vitro and in vivo assays have been developed to study the relative contributions of various types of immune cytolysis in the destruction of infected cells after Semliki Forest virus infection of BALB/c mice. Highly cytotoxic activated macrophages, not specific for the infecting virus, appear on day 1, peak on day 2 to 3, and disappear within a week. Specifically sensitized T cells appear around day 3, peak on day 6, and disappear within a month. Cytotoxic antibody appears on day 4 and reaches high titers by day 8. Immune spleen cells greatly reduce the yield of virus from cultured cells. Infected cells rapidly disappear after transfer to infected animals.     

An XY sex chromosome mechanism in a mantid with achiasmatic meiosis

An Australian mantid, Ima fusca, with 2n male equals 34, shows achiasmatic meiosis in the male, as in other Australian members of the subfamily Iridopteryginae. It is, however, unique among approximately 104 mantid species that have been studied cytologically, in having an XY sex chromosome mechanism. The X and Y chromosomes are not associated as a bivalent in first metaphase, but arrange themselves opposite one another on the spindle and regularly pass to different poles at first anaphase.