Terminal phase of cytokinesis in D-98S cells

The events leading to the completion of cytokinesis after the formation of the midbody and intercellular bridge in D-98S cells were studied with light and electron microscopy. Pairs of daughter cells corresponding to different stages of cytokineses, as determined previously form time lapse films, were selected from embedded monolayers for serial sectioning. Separation of daughter cells is preceded by the reduction in diameter of the intercellular bridge from 1-1.5 μm to approx. 0.2 μm. Two processes contribute to this reduction: (a) The intercellular bridge becomes gradually thinner after telophase; a progressive breakdown of midbody structures accompanies this change; and (b) the more significant contribution to reduction in bridge diameter occurs through the localized constriction of a segment of the intercellular bridge.. The microtubules within the constricted portion of the bridge are forced closer together, and some microtubules disappear as this narrowing progresses. The plasma membrane over the narrowed segments is thrown into a series of wavelike ripples. Separation of daughter cells is achieved through movements of the cells which stretch and break the diameter-reduced bridge. The midbody is discarded after separation and begins to deteriorate. Occasional pairs of daughter cells were found in which incomplete karyokineses resulted in their nuclei being connected by a strand of nuclear material traversing the bridge and midbody. Such cells do not complete cytokinesis but merge together several hours after telophase. This merging of daughter cells coincides with the nearly complete breakdown of the midbody.     

Effects of habitat enrichment and food availability on the foraging behaviour of juvenile Atlantic Cod (<Emphasis Type="Italic">Gadus morhua L</Emphasis>)

The environment can play an important role in shaping how an animal behaves, and how well the animal performs in a particular environment can be influenced by early experiences. The tradition of releasing captive-reared juveniles into the wild in an effort to strengthen wild fish populations has often had little success owing to high post-release mortality. Fish reared under standard hatchery conditions are provided with fewer stimuli and they receive excess quantities of pellet food that are easy to handle and consume. Captive reared fish therefore appear to be under-stimulated and overfed. Several studies have demonstrated that simple structural enrichment in the rearing facilities promotes flexible behaviour compared to fish reared in plain, standard hatchery tanks. Less attention has been given to the effects of the diet. Here we use a cross-factored design to test the relative role of food ration and spatial enrichment on foraging behaviour. Our results show that fish from enriched environments, regardless of previous food-ration size, were more reluctant to start feeding on the first day in a novel arena. On day two and three, however, fish with prior experience of a low food ration showed greater foraging activity and efficiency than fish fed on full rations. On the second and third day, prior experience with enrichment was less important. We discuss how early feeding experience in combination with structural enrichment may contribute in producing fish that are better suited for release into the wild.     

Sexual selection,germline mutation rate and sperm competition

Background  

An important component of sexual selection arises because females obtain viability benefits for their offspring from their mate choice. Females choosing extra-pair fertilization generally favor males with exaggerated secondary sexual characters, and extra-pair paternity increases the variance in male reproductive success. Furthermore, females are assumed to benefit from 'good genes' from extra-pair sires. How additive genetic variance in such viability genes is maintained despite strong directional selection remains an evolutionary enigma. We propose that sexual selection is associated with elevated mutation rates, changing the balance between mutation and selection, thereby increasing variance in fitness and hence the benefits to be obtained from good genes sexual selection. Two hypotheses may account for such elevated mutation: (1) Increased sperm production associated with sperm competition may increase mutation rate. (2) Mutator alleles increase mutation rates that are revealed by the expression of condition-dependent secondary sexual characters used by choosy females during their mate choice. M Petrie has independently developed the idea that mutator alleles may account for the maintenance of genetic variation in viability despite strong directional selection.     

Inhibition of host-seeking response and olfactory responsiveness in Anopheles gambiae following blood feeding

The effect of a single blood meal on the host-seeking response of Anopheles gambiae was investigated in the laboratory using a behavioural bioassay, whereas possible changes at the chemosensory level were monitored using electroantennogram recording (EAG). To avoid the possible confounding effect of body size, mosquitoes of a large size class only were used. Five-day old female mosquitoes were given a blood meal on a human arm and exposed to the emanations of a human hand in an olfactometer at 3, 24, 40, 48 and 72 h following the meal and their behaviour and EAG response to host stimuli were compared with that of unfed mosquitoes (controls) of corresponding age. During egg development, mosquitoes had access to glucose and an oviposition tray. The ovarian development of blood-fed mosquitoes that responded to host odours was compared with that of blood-fed mosquitoes that had not been exposed to host odours. The EAG response of blood-fed and control mosquitoes to host odour was examined upon stimulation with air led over incubated human sweat, hexanoic acid, indole and geranyl acetone. EAGs were recorded at times after a blood meal corresponding with those used in the behavioural experiment. There was no host-seeking response at 3 and 24 h post blood meal (pbm). Seven percent of the mosquitoes responded to human emanations 40-h pbm, 27% at 48 h and 68% at 72 h following a blood meal. The average response of controls to host stimuli varied from 35 (at t=40 h) to 67%. There was no ovarian development in the unfed group of mosquitoes. Of the mosquitoes that responded to host odour 48 h pbm, 12.5% (n=5) had ovaries in Christophers' stage IV and the remainder in stage V. Of the mosquitoes that responded 72 h pbm, 66.7% (n=94) had ovaries in stage V and 31.2% (n=44) had recently oviposited. Maximum EAG amplitudes recorded from blood-fed and control mosquitoes were similar for mosquitoes in Christophers' stages I-III, whereas in stage IV EAG amplitudes recorded from the blood-fed group were significantly lower than those of the corresponding control group in response to headspace of incubated human sweat and to indole. The results show that there was a strong inhibition of host seeking in An. gambiae for a period of at least 40 h following a blood meal. Host-seeking returned to pre-blood meal levels 72-h post feeding and was associated with egg maturation. The inhibition of host-seeking behaviour was accompanied by an inhibition of olfactory sensitivity to headspace of incubated sweat and indole just before the resumption of the host-seeking response. The implications of these findings for mosquito surveillance with host odours are discussed.     

Heterologous expression of bacteriocin E-760 in Chlamydomonas reinhardtii and functional analysis

The use of antimicrobial peptides (AMPs) synthesized by bacteria (bacteriocins) is an alternative for combating multidrug resistant bacterial strains and their production by recombinant route is a viable option for their mass production. The bacteriocin E-760 isolated from the genus Enterococcus sp. has been shown to possess inhibitory activity against Gram-negative and Gram-positive bacteria. In this study, the expression of a chimeric protein coding for E-760 in the nucleus of C. reinhardtii was evaluated, as well as, its antibacterial activity. The synthetic gene E-760S was inserted into the genome of C. reinhardtii using Agrobacterium tumefaciens. A transgenic line was identified in TAP medium with hygromycin and also by PCR. The increment in the culture medium temperature of the transgenic strain at 35 °C for 10 minutes, increased the production level of the recombinant protein from 0.14 (Noninduced culture, NIC) to 0.36% (Induced culture, IC) of total soluble proteins (TSP); this was quantified by an ELISA assay. Recombinant E-760 possesses activity against Staphylococcus aureus in 0.34 U log, Streptococcus agalactiae in 0.48 U log, Enterococcus faecium in 0.36 U log, Pseudomonas aeruginosa in 2 U log and for Klebsiella pneumoniae, the activity was 0.07 U log. These results demonstrate that the nucleus transformation of C. reinhardtii can function as a stable expression platform for the production of the synthetic gene E-760 and it can potentially be used as an antibacterial agent.