The nucleotide receptor P2X7 has been shown to modulate LPS-induced macrophage production of numerous inflammatory mediators. Although the C-terminal portion of P2X7 is thought to be essential for multiple receptor functions, little is known regarding the structural motifs that lie within this region. We show here that the P2X7 C-terminal domain contains several apparent protein-protein and protein-lipid interaction motifs with potential importance to macrophage signaling and LPS action. Surprisingly, P2X7 also contains a conserved LPS-binding domain. In this report, we demonstrate that peptides derived from this P2X7 sequence bind LPS in vitro. Moreover, these peptides neutralize the ability of LPS to activate the extracellular signal-regulated kinases (ERK1, ERK2) and to promote the degradation of the inhibitor of κB-α isoform (IκB-α) in RAW 264.7 macrophages. Collectively, these data suggest that the C-terminal domain of P2X7 may directly coordinate several signal transduction events related to macrophage function and LPS action.

Previous studies have suggested that the P2Z/P2X 7 purinergic receptor can participate in nucleotide-induced modulation of lipopolysaccharide (LPS) stimulated inflammatory mediator production. To test this hypothesis, we evaluated whether antagonism of the P2Z/P2X 7 receptor can influence LPS signaling and expression of the inducible form of nitric-oxide synthase (iNOS) in RAW 264.7 macrophages. In the present study, we demonstrate that pretreatment of RAW 264.7 macrophages with a P2Z/P2X 7 receptor antagonist, periodate oxidized adenosine 5-triphosphate (o-ATP), substantially inhibits LPS-stimulated NO production and iNOS expression without altering cell viability. This effect on LPS-induced iNOS expression is mimicked by a pyridoxal-phosphate-based antagonist (pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid) of the P2Z/P2X 7 purinergic receptor, indicating that these results are not unique to o-ATP. Additionally, o-ATP prevents cell death induced by P2Z/P2X 7 receptor agonists. To ascertain how P2Z/P2X 7 receptor antagonists influence LPS signaling, we evaluated the capacity of o-ATP to regulate LPSmediated activation of the transcription factor, nuclear factor-B, and the mitogen-activated protein kinases, extracellular signal-regulated kinase (ERK) 1 and ERK2. These experiments reveal that pretreatment of RAW 264.7 cells with o-ATP attenuates the LPS stimulation of a nuclear factor-B-like binding activity. Moreover, the activation of ERK1 and ERK2 by LPS, but not by the phorbol ester, phorbol 12-myristate 13-acetate, is also blocked in RAW 264.7 cells by o-ATP pretreatment. In summary, these data suggest that the P2Z/P2X 7 receptor modulates LPS-induced macrophage activation as assessed by iNOS expression and NO production. This report implicates the P2Z/P2X 7 receptor in the control of protein kinase cascades and transcriptional processes, and these observations are likely to be important for the development of selective purinergic receptor antagonists for the treatment of septic shock.

Phylogenetic analysis of ca. 4500 base pairs of mitochondrial DNA sequence data reveals further genetic diversity in mouse lemurs (Microcebus) on the eastern and western coasts of Madagascar. Molecular data and phylogenetic analyses revise the previously monotypic species of eastern Madagascar, Microcebus rufus, with the description of 3 new species. Three additional Microcebus species are proposed in eastern Madagascar, along with another Microcebus species in western Madagascar. Correlating the molecular data with previously generated sequence data, we present a tentative pattern of distribution along the east coast. We show that the general distribution of Microcebus is based on a traditional eastern/western division. The preliminary model appears strongly influenced by both rivers and altitudinal differences acting independently as barriers.

Parthenogenesis has been documented in all major jawed vertebrate lineages except mammals and cartilaginous fishes (class Chondrichthyes: sharks, batoids and chimeras). Reports of captive female sharks giving birth despite being held in the extended absence of males have generally been ascribed to prior matings coupled with long-term sperm storage by the females. Here, we provide the first genetic evidence for chondrichthyan parthenogenesis, involving a hammerhead shark (Sphyrna tiburo). This finding also broadens the known occurrence of a specific type of asexual development (automictic parthenogenesis) among vertebrates, extending recently raised concerns about the potential negative effect of this type of facultative parthenogenesis on the genetic diversity of threatened vertebrate species.

No abstract