Quantitative ultrastructural analysis of barley sperm

Summary Complete serial ultrathin sections of seven sperm pairs, computer-assisted measurements of cell, nuclear and organelle surface areas and volumes, and three-dimensional imagery were used to demonstrate that a process of cytoplasm and organelle elimination occurs during sperm maturation in barley. The number of mitochondria per sperm cell is reduced by 50%; sperm cell surface area and volume are reduced by 30% and 51% respectively. Mean volume and surface area per mitochondrion are significantly less in mature sperms. No examples of mitochondrial fusion or degeneration were observed within sperm cells. These data, along with observations of plasma membrane apposition and vesiculation within cytoplasmic extensions containing mitochondria, support the proposition that cytoplasm and organelle loss results primarily from the formation of cytoplasmic projections that are subsequently discarded from the sperm cell body. Comparisons of the quantitative data, including the number of mitochondria, indicate that differences between sperm cells of a pair are absent to very slight. Spatial organization within the pollen grain is such that the mature sperms, as well as the sperms and vegetative nucleus, are not in close proximity.     

Isolation of low-copy-number sequences that neighbor satellite DNA in mammals

To investigate the role of satellite DNA in eukaryotic genomes, we isolated from an African green monkey (Cercopithecus aethiops) genomic library cloned segments containing the previously described deca-satellite linked to low-copy-number genomic sequences. Three such clones were obtained. The low-copy-number sequences in the three clones do not cross-hybridize suggesting that they derive from different genomic loci. The structure of one of the clones, λAMkA, is described in detail. Subcloned segments containing the low-copy-number sequences from λAMkA anneal to monkey, human and mouse genomic DNA. The subcloned probes were used to select clones containing homologous sequences from a second, independent monkey library as well as from human and mouse genomic libraries. Several of the newly isolated monkey clones hybridized to probes containing the species-specific deca- and -satellites, confirming the genomic association of the low-copy-number sequence in λAMkA with satellite DNA. Moreover, several of the human and mouse clones hybridized to species-specific human and mouse satellite DNAs, respectively. These experiments indicate that the low-copy-number sequence in λMkA and its association with satellite DNA is conserved in primates and rodents.     

The Kinetics of Sodium Transport in the Toad Bladder : I. Determination of the transport pool

A compartmental model of toad bladder sodium content has been developed, whereby it is possible to measure the four unidirectional fluxes across the opposite faces of the transport compartment, as well as the amount of sodium in the compartment. ²⁴Na is added to the mucosal medium of a short-circuited bladder mounted between halves of a chamber in which the fluid is stirred by rotating impellers. After a steady state is reached, nonradioactive medium is flushed through both sides of the chamber, collected, and counted. The data from each chamber are fitted to sums of exponentials and interpreted in terms of conventional compartmental analysis. Three exponentials are required, with half-times of 0.2, 2.2, and 14.0 min. It is shown that the first of these represents chamber washout, the second the transport pool, and the third a tissue compartment which is not involved in active sodium transport and which does not communicate with the transport pool. The second compartment contains 10.5 µEq of sodium per 100 mg dry weight, an amount equal to approximately 30% of total tissue sodium. The results also indicate, as expected from electrophysiological data, that the mucosal-facing side of the transport compartment is over 10 times as permeable to sodium as the serosal, or pump, side.     

Limitations of Fibrinogen-Polymyxin Medium in Detecting Coagulase-Positive Staphylococci in Raw Milk

A fibrinogen-polymyxin medium and Staphylococcus Medium 110 were used in the isolation of coagulase-positive staphylococci in raw milk. Results indicated that both media allow the growth of some rods and of many coagulase-negative cocci. A significantly greater number of coagulase-positive staphylococci were identified by the tube test than were revealed by halo formation on fibrinogen-polymyxin medium.     

Effects of epidermal growth factor on apo B mRNA levels and apo B accumulation in the media of primate hepatocytes in culture.

EGF has been shown to augment albumin and apolipoprotein A-I secretion by cynomolgus monkey hepatocytes in primary culture without stimulating cell division. This study was undertaken to determine what effect EGF had on apo B secretion by those hepatocytes. The results indicate that EGF (3 nM final concentration) severely inhibits the rate at which apo B accumulates in the culture medium of primate hepatocytes. That effect was evident within 48 hours of treatment, and by 72 hours the rate that apo B accumulated was less than half that of cells treated with a hormone-free medium. However, the apo B mRNA levels in the EGF-treated cells were more than double those of hepatocytes given the hormone-free medium. These data indicate that EGF has a potent effect on the rate at which apo B accumulates in the culture medium of primate hepatocytes and that the effect is independent of apo B gene expression.     

A new major histocompatibility complex class I b gene expressed in the mouse blastocyst and placenta

 Because of the role major histocompatibility complex (MHC) class I b molecules may play during mouse embryonic development, we thought it would be interesting to search for additional MHC class I b molecules that might be expressed in preimplantation embryos, and in particular in the trophoblastic lineage. We therefore screened a mouse preimplantation blastocyst cDNA library for MHC class I sequences. This search led to the identification and characterization of a new MHC class I b gene, blastocyst MHC. Sequences identical to the exons and 3′ untranslated region of this gene have been found in many laboratory mouse strains, as well as in the related mouse species Mus spreciligus. The presence of this gene in mouse strains of different MHC class I haplotypes argues that blastocyst MHC is a unique, newly-described gene rather than a new allele of a previously described mouse MHC class I gene. Blastocyst MHC has the structure of an MHC class I b gene, with the six exons characteristic of T-region genes. It is linked to H2-D. The amino acid sequence encoded by this gene maintains all the features of a functional antigen-presentation domain. The blastocyst MHC gene, like the human class I b gene HLA-G, is expressed at the blastocyst stage and in the placenta, and may be the mouse analog for HLA-G. Received: 31 May 1996 / Revised: 19 August 1996     

Ubiquitin‐specific protease‐like 1 (USPL1) is a SUMO isopeptidase with essential,non‐catalytic functions

Isopeptidases are essential regulators of protein ubiquitination and sumoylation. However, only two families of SUMO isopeptidases are at present known. Here, we report an activity‐based search with the suicide inhibitor haemagglutinin (HA)‐SUMO‐vinylmethylester that led to the identification of a surprising new SUMO protease, ubiquitin‐specific protease‐like 1 (USPL1). Indeed, USPL1 neither binds nor cleaves ubiquitin, but is a potent SUMO isopeptidase both in vitro and in cells. C13orf22l—an essential but distant zebrafish homologue of USPL1—also acts on SUMO, indicating functional conservation. We have identified invariant USPL1 residues required for SUMO binding and cleavage. USPL1 is a low‐abundance protein that colocalizes with coilin in Cajal bodies. Its depletion does not affect global sumoylation, but causes striking coilin mislocalization and impairs cell proliferation, functions that are not dependent on USPL1 catalytic activity. Thus, USPL1 represents a third type of SUMO protease, with essential functions in Cajal body biology.     

Lipoprotein metabolism in the ovariectomized rat

The hyperlipoproteinemia observed after ovariectomy in rats was previously shown to be associated with increased concentrations of cholesterol, triglycerides, and apolipoproteins B, E, and C. In the present study, it was shown that increases in low density lipoproteins and high density lipoproteins were almost entirely responsible for the changes in plasma lipids and apolipoproteins after ovariectomy. The size of the low density lipoproteins and high density lipoproteins isolated from the plasma of ovariectomized rats as determined by agarose chromatography appeared to be somewhat different from that of control rats. Specifically, the apolipoprotein B appeared to be associated with somewhat smaller particles, whereas the apolipoprotein E from those rats appeared to be associated with larger particles than that of control rats. To determine the mechanism for the increased plasma low density lipoproteins, apolipoprotein B pool sizes and turnover rates were calculated and compared. In addition to an increased mass of low density lipoproteins in ovariectomized rats, the turnover rate of low density lipoproteins was increased almost twofold, indicating an increased low density lipoprotein synthesis and catabolism in those animals. We postulate that the increased low density lipoprotein levels of ovariectomized rats are due to an initial increased production of low density lipoproteins, followed by an enhanced catabolism of low density lipoproteins to establish a steady state at higher plasma low density lipoprotein concentrations.     

CYTOGENETICS OF RUBUS. II. CYTOLOGICAL STUDIES OF THE VARIETIES ‘YOUNG,’ ‘BOYSEN,’ AND RELATED FORMS

Thompson , Maxine M. (U. California, Davis.) Cytogenetics of Rubus. II. Cytological studies of the varieties ‘Young,’ ‘Boysen’ and related forms. Amer. Jour. Bot. 48(8): 667–673. Illus. 1961.—Chromosome numbers are given for the trailing blackberry varieties, ‘Young’ (2n = 49), ‘Boysen’ (2n = 49), ‘Nectar’ (2n = 49) and for related forms which include the parents of ‘Young,’ ‘Phenomenal’ (2n = 42) and ‘Mayes’ (2n = 56), and 3 cytologically resynthesized ‘Young’ plants (2n = 49) as a basis for interpreting the postulated origin of ‘Young.’ Cytological evidence substantiated the conclusion that ‘Young’ is a hybrid between ‘Phenomenal’ and ‘Mayes.’ Contributions to the understanding of genomic relationships in Rubus are offered from detailed analyses of meiosis in ‘Phenomenal,’ ‘Mayes,’ ‘Young,’ and ‘Boysen.’ ‘Phenomenal’ and ‘Mayes’ both had a very regular meiosis. ‘Young,’ as well as ‘Boysen,’ showed a greater degree of chromosome association than either parent of ‘Young.’ Meiotic behavior in ‘Boysen’ presented a close parallel to that of ‘Young’ which, correlated with morphological similarities and the same 2n chromosome number, suggests a similar origin. The mode of reproduction in ‘Young’ and ‘Boysen’ was found to be sexual on the basis of morphological variation in the open-pollinated (selfed) progeny, the varying aneuploid somatic chromosome numbers in these progeny (2n = 32–54) and aneuploid chromosome numbers in hybrids having either variety as one parent. The productiveness of ‘Young’ and ‘Boysen’ in commercial plantings and their successful utilization in breeding programs indicate a high fertility regardless of their having an odd multiple of the basic number. It is concluded that the production of balanced euploid gametes is not necessarily a criterion of fertility, at least not at this high level of ploidy.