Reproductive Isolation in a Threespine Stickleback Hybrid Zone

In many estuarine sites, morphological and genetic differences between anadromous and freshwater threespine sticklebacks are maintained despite breeding in sympatry. Here, we investigate the maintenance of this morphological divergence in a natural hybrid zone in the River Tyne, Scotland. We provide a morphological description of the hybrid zone, and using a Bayesian MCMC approach, identified distinct anadromous and freshwater genetic clusters. Anadromous and freshwater sticklebacks breed in spatial and temporal sympatry in the lower reaches of the River Tyne. The frequency of hybrids within these sites (33%) indicates prezygotic isolation is not complete, and suggests that assortative mating is not strong. However, significant heterozygote deficit and cytonuclear disequilibrium in juveniles collected from sympatric sites confirms that barriers to gene flow exist between the morphs in the wild. In addition, we found no evidence of a directional bias in hybridisation, although hybrids with anadromous mothers were more common because anadromous females outnumbered freshwater females within the hybrid zone. We discuss the potential contribution of temporal, spatial, and sexual prezygotic barriers to the observed reproductive isolation as well as postzygotic selection against hybrid zygotes or fry

In vitro and in vivo effects of treatment by platelet-activating factor on N-formyl-met-leu-phe-mediated responses of polymorphonuclear leucocytes

Two chemoattractants, the peptide N-formyl-met-leu-phe (FMLP), and the ether phospholipid, platelet activating factor (PAF), each stimulate a variety of in vitro responses in polymorphonuclear leucocytes (PMN). Because often more than one inflammatory mediator is active during inflammation, we determined the effect on PMN of sequential stimulation with these two agents. Before FMLP stimulation, human PMN were exposed to PAF, at concentrations which gave little or no response when administered alone. PAF enhanced FMLP-elicited superoxide release in a dose-dependent fashion. Likewise, release of granular lysozyme from the cells was increased in PAF treated cells. Similar treatment with other phospholipids, including the lyso derivation of PAF, failed to produce these effects. Incubation with nordihydro-guaiaretic acid, an inhibitor of arachidonic acid metabolism, had little effect on the enhancement of lysozyme release by PAF. To determine if enhancing effects by PAF might occur also in vivo , we studied rabbits receiving PAF and/or FMLP intravenously. When rabbits received 0·01 Μg PAF (a dose which does not elicit the sustained neutropenia observed with higher doses of PAF) followed by 0·05 Μg FMLP the absolute granulocyte count (AGC) dropped at 1 min (46 ± 11% of original value), and continued to fall (24 ± 12% at 10 min). Controls, treated with the suspending fluid for PAF, and then 0·05 Μg FMLP, had a similar 1 min AGC value, but at 10 min AGC returned to 65±6·1% ( P <0·001 for comparison of 10 min values). Thus PAF pretreatment enhanced FMLP-elicited granulocytopenia in vivo . Study of in vitro human PMN aggregation revealed that, at certain relative concentrations of PAF and FMLP. aggregation was enhanced. These studies show that both in vitro and in vivo responses of FMLP-stimulated PMN may be exaggerated by pre-exposure to PAF.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72047/1/j.1365-2141.1987.tb01302.x.pd

Antigen-stimulated Activation of Phospholipase D1b by Rac1, ARF6, and PKCα in RBL-2H3 Cells

Phospholipase D (PLD) activity can be detected in response to many agonists in most cell types; however, the pathway from receptor occupation to enzyme activation remains unclear. In vitro PLD1b activity is phosphatidylinositol 4,5-bisphosphate dependent via an N-terminal PH domain and is stimulated by Rho, ARF, and PKC family proteins, combinations of which cooperatively increase this activity. Here we provide the first evidence for the in vivo regulation of PLD1b at the molecular level. Antigen stimulation of RBL-2H3 cells induces the colocalization of PLD1b with Rac1, ARF6, and PKCα at the plasma membrane in actin-rich structures, simultaneously with cooperatively increasing PLD activity. Activation is both specific and direct because dominant negative mutants of Rac1 and ARF6 inhibit stimulated PLD activity, and surface plasmon resonance reveals that the regulatory proteins bind directly and independently to PLD1b. This also indicates that PLD1b can concurrently interact with a member from each regulator family. Our results show that in contrast to PLD1b's translocation to the plasma membrane, PLD activation is phosphatidylinositol 3-kinase dependent. Therefore, because inactive, dominant negative GTPases do not activate PLD1b, we propose that activation results from phosphatidylinositol 3-kinase–dependent stimulation of Rac1, ARF6, and PKCα