Antigen presentation by the BCL1 murine B cell line: in vitro stimulation by LPS

We examined the antigen-presenting capacity of BCL1 tumor cells, which are capable of differentiating in vitro with respect to immunoglobulin synthesis/secretion under the influence of LPS. In vivo passaged BCL1 cells depleted of host cell contamination either by positive selection employing panning with anti-lambda reagents, or by elimination of latex-ingesting adherent cells, are capable of MHC-restricted antigen presentation to a GAT-immune T cell line. The BCL1 cells act as antigen-presenting cells when freshly explanted, but gradual loss of this function occurs, and cells cultured for 3.5 days cannot present antigen unless LPS is included during the culture period. BCL1 cells are equivalently Ia+ after the culture period with or without LPS stimulation. Other B cell lines capable of antigen presentation appear to express this trait constitutively, and the in vivo passaged BCL1 line is therefore unique among B cell lines in having antigen-presenting cell function that can be modulated. The data suggest that freshly explanted or LPS-cultured BCL1 cells are heterogeneous with respect to antigen-presenting capacity, and the basis for this heterogeneity is being sought. BCL1 offers an opportunity to study requirements for antigen presentation by B cells.     

Comparison of factor IX methylation on human active and inactive X chromosomes: implications for X inactivation and transcription of tissue-specific genes.

Maintenance of dosage compensation for housekeeping genes on the human X chromosome is mediated through differential methylation of clustered CpG nucleotides associated with these genes. To determine if methylation has a role in maintaining inactivity of X-linked genes which show tissue-specific expression, we examined the locus for blood clotting Factor IX. The analysis encompassed 91% of the HpaII and HhaI sites in the 41-kb region that includes the presumed promoter region, 5 kb of 5'- and 4 kb of 3'-flanking sequences. Although there are sex differences in methylation of the locus in leukocytes, the methylation pattern in liver, where the gene is expressed, is essentially the same for loci on the active and inactive X chromosome. The lack of differences in methylation of active and inactive genes makes it unlikely that methylation within the locus has a role in expression of the Factor IX gene. These findings, along with the absence of clustered CpG dinucleotides within the Factor IX locus, suggest that functional differences in DNA methylation related to X chromosome dosage compensation may be limited to CpG clusters. In any event, dosage compensation seems to be maintained regionally, rather than locus by locus.     

The kinetics of algal photoadaptation in the context of vertical mixing

The responses of phytoplankton to turbulent motions in the surfacemixed layer can be measured to estimate the rate of verticalmixing. If the time scale for the response (photoadaptation)is shorter than that for vertical mixing, phytoplankton willexhibit a vertical gradient associated with adaptation to ambientlight, whereas if mixing occurs with a time scale shorter thanthat of photoadaptation, the surface mixed layer will be uniformwith respect to the photoadaptive parameter. To examine thephysiological bases for a model of vertical mixing and photoadaptation,we grew the marine diatom Thalassiosira pseudonana (clone 3H)at three photon flux densities and subjected the cultures toreciprocal light shifts, measuring physiological and chemicalchanges over the following 10 h. Several parameters, easilymeasured in nature and attributable primarily to phytoplankton,responded to fluctuating light on different time scales. Aftercultures were exposed to relatively bright light, both the initialslope of the photosynthesis-irradiance curve and in vivo fluorescencewere depressed on a time scale of less than an hour. Photosyntheticcapacity was also reduced transiently, but recovered over manyhours to a high level characteristic of an adapted state. First-orderkinetics (the current model of choice for describing photoadaptation)reasonably described the rapid responses of phytoplankton tobright light, but other parameters (i.e. cellular chemical compositionand photosynthetic capacity) changed as a result of unbalancedgrowth and required much longer to adapt from low to high lightas compared to from high to low light. A logistic model of thisadaptation is presented. The model suggests that hysteresisof adaptation during vertical mixing may have important consequences.The vertical distributions of photoadaptive properties in mixedlayers not only reveal the rate of vertical mixing, but showhow phytoplankton integrate environmental fluctuations.     

Parameters of growth in primary cultures and cell lines established from Drosophila imaginal discs

We have further characterised our tissue culture system for the growth in vitro of Drosophila imaginal disc cells, including the culture medium requirements for optimum growth and we have adjusted the protocol recommended for the initiation of cultures. Many imaginal disc fragments become organised into vesicles, and some of these secrete extracellular material into the lumen. Sensory axons differentiate in primary disc cultures, in the absence of bristle formation. The early stages of cell division to form a cell line are recorded.     

Analysis of the sheep MHC using HLA class I,II, and C4 cDNA probes

Four cDNA probes for the human major histocompatibility complex (MHC) were used to investigate the sheep MHC, in conjunction with serological typing for ovine lymphocyte antigen (OLA). Lymphocytes from a family (two parents and five offspring) of Romanov sheep were subjected to genomic DNA digestion by the restriction endonuclease Eco RI, followed by gel electrophoresis. A single Southern blot representing all seven individuals was then consecutively hybridized with the class I, alpha-DC, beta-DR, and C4 probes, which were originally designed to identify HLA class I, class II (DC and DR), and C4 products, respectively. Using each of the three class I/class II probes, several bands showing DNA polymorphism were detected. The segregation of these bands in the five offspring exactly paralleled the OLA haplotype segregation established by serological typing. A further eight individuals carrying haplotypes which were phenotypically identical to those in the above-mentioned family showed bands in the corresponding positions when tested with the same three probes. Using the C4 probe, no polymorphism was detected in these fifteen individuals.Abbreviations used in this paper MHC major histocompatibility complex - OLA ovine lymphocyte antigen - kbp kilobase pair(s) - MLR mixed lymphocyte reaction - RFLP restriction fragment length polymorphism     

Experiments on whether schooling by their prey affects the hunting behaviour of cephalopods and fish predators

The experiments investigated the effects of a school of live prey fish on the hunting behaviour of squid, cuttlefish and pike (ambush predators) and perch (a chasing predator). The hunting behaviour of all species is described, including some previously unrecorded actions.
For all species the increasing shoal size from one fish to six, to 20, decreased the success of the predators' attacks per encounter with a prey. This was partly because attacks on larger shoals lasted longer, and fish became increasingly difficult to catch as a hunt went on. However, for some of the species there was a clear effect of the shoals at the start of the hunt. For other species it was less conclusive.
The disruptive effect of the shoals was shown to act for the ambush predators by interfering with the "optimal" sequence of an attack and causing avoidance actions together with so-called irrelevant behaviour. For the perch, shoals seemed to disrupt by forcing the predator continually to switch targets during his pursuit.
The artificiality of the experiments is discussed in relation to field observations. The relatively high incidence of avoidance and irrelevant behaviour seems to be an artefact, but the main results are quite compatible with field studies. In nature fish predators may be able to get sufficient food by restricting their attacks to individuals which are conspicuous either by an abnormal appearance or by becoming separated from the school. An individual prey fish no doubt gains a considerable advantage from the school by burying itself in the crowd. Our experiments show that a shoal can provide further protection in hampering the attack of a predator.