Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure?

Summary It has been suggested by Cohen and Newman (1985) that many of the patterns in published food webs can be derived from a stochastic model in which the species are arranged in a trophic hierarchy (the cascade model). We suggest that, if predators are larger than their prey, a trophic hierarchy can be generated on the basis of body size Empirical evidence from the literature shows that there is a positive relationship between predator and prey size for a range of invertebrates and that predators are usually larger than their prey. Using experimental data on an aquatic food web we show that body size can lead to the type of trophic hierarchy used in the cascade model, suggesting that many food web patterns may be a product of body size. This conclusion is discussed with respect to the limitations of the food web data and the relationship between static and dynamic models of web structure.     

A mitotic form of the Golgi apparatus in HeLa cells

Galactosyltransferase, a marker for trans-Golgi cisternae in interphase cells, was localized in mitotic HeLa cells embedded in Lowicryl K4M by immunoelectron microscopy. Specific labeling was found only over multivesicular structures that we term Golgi clusters. Unlike Golgi stacks in interphase cells, these clusters lacked elongated cisternae and ordered stacking of their components but did comprise two distinct regions, one containing electron-lucent vesicles and the other, smaller, vesiculo-tubular structures. Labeling for galactosyltransferase was found predominantly over the latter region. Both structures were embedded in a dense matrix that excluded ribosomes and the cluster was often bounded by cisternae of the rough endoplasmic reticulum, sometimes on all sides. Clusters were present at all stages of mitosis examined, which included prometaphase, metaphase, and telophase. They were also identified in conventionally processed mitotic cells and shown to contain another trans-Golgi marker, thiamine pyrophosphatase. Serial sectioning showed that clusters were discrete and globular and multiple copies appeared to be dispersed in the cytoplasm. Their possible role in the division of the Golgi apparatus is discussed.     

Lymphoma models for B cell activation and tolerance. VI. Reversal of anti-Ig-mediated negative signaling by T cell-derived lymphokines

We have recently described three "immature" B cell lymphomas which are exquisitely sensitive to growth inhibition by anti-Ig reagents and may serve as models for tolerance induction in normal B cells. These cells are inhibited from cell cycle progression into S after receiving a negative signal in early G1. In this paper, we demonstrate that the growth inhibition by anti-Ig can be prevented and reversed by the addition of supernatants from T cell lines. One such line, called Tova, produces factors which restore normal levels of DNA synthesis in the presence of concentrations of anti-Fab or anti-kappa immunoglobulins which cause up to a 90% inhibition of thymidine incorporation in a 2- to 3-day culture period. This factor is at least partially effective when added up to 24 hr after anti-Ig to unsynchronized lymphoma cells and it does not alter the growth of control cultures. Studies using synchronized lymphoma cells indicated that the T cell factor permitted cycle progression into S when added during the early G1 exposure to anti-kappa and was less effective when added late in G1. Preliminary characterization suggests that both B cell growth factor II (interleukin 5) and B cell stimulatory factor 1 (interleukin 4) have additive activity in this system, although another unidentified lymphokine may also be involved. The relevance of T cell reversal of Ig receptor-mediated negative signaling to neonatal B cell tolerance is emphasized.     

A reply to Holmes on Gendercide

Warren's book, Gendercide: The Implications of Sex Selection (Totowa, N.J.: Rowman and Allanheld; 1985), was reviewed by Helen Bequaert Holmes in the January 1987 issue of Bioethics. Here, Warren responds to the review by clarifying some of her moral arguments and continuing to defend the point of view that selecting the sex of children before conception or before birth is not always sexist, socially harmful, or disrespectful of the child as an end in itself.     

Genetic deletions between directly repeated sequences in bacteriophage T7

Summary DNA sequence analysis of genetic deletions in bacteriophage T7 has shown that these chromosomal rearrangements frequently occur between directly repeated DNA sequences. To study this type of spontaneous deletion in more quantitative detail synthetic fragments of DNA, made by hybridizing two complementary oligonucleotides, were introduced into the non-essential T7 gene 1.3 which codes for T7 DNA ligase. This insert blocked synthesis of functional ligase and made the phage that carried an insert unable to form plaques on a host strain deficient in bacterial ligase. The sequence of the insert was designed so that after it is put into the T7 genome the insert is bracketed by direct repeats. Perfect deletion of the insert between the directly repeated sequences results in a wild-type phage. It was found that these deletion events are highly sensitive to the length of the direct repeats at their ends. In the case of 5 bp direct repeats excision from the genome occurred at a frequency of less than 10⁻¹⁰, while this value for an almost identical insert bracketed by 10 bp direct repeats was approximately 10⁻⁶. The deletion events were independent of a hostrecA mutation.