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Study of the structure of savanna elephant populations and gene flow across eastern and southern Africa by examining the patterns of restriction site variation within mitochondrial DNA suggests that clades that diverged at least four million years ago persist in a population that was distinct but not completely isolated in allopatry. One haplotype is found at all the locations, while the haplotypes derived from divergent mitochondrial clades are found at sampling locations further away.

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Background and Purpose: Glutamate transporters play a major role in maintaining brain homeostasis and the astrocytic transporters, EAAT1 and EAAT2, are functionally dominant. Astrocytic excitatory amino acid transporters (EAATs) play important roles in various neuropathologies wherein astrocytes undergo cytoskeletal changes. Astrocytic plasticity is well documented, but the interface between EAAT function, actin and the astrocytic cytoskeleton is poorly understood. Because Rho kinase (ROCK) is a key determinant of actin polymerization, we investigated the effects of ROCK inhibitors on EAAT activity and astrocytic morphology.Experimental Approach: The functional activity of glutamate transport was determined in murine cultured astrocytes after exposure to the ROCK inhibitors Fasudil (HA-1077) and Y27632 using biochemical, molecular and morphological approaches. Cytochemical analyses assessed changes in astrocytic morphology, F-/G-actin, and localizations of EAAT1/2.Results: Fasudil and Y27632 increased [(3)H]-D-aspartate (D-Asp) uptake into astrocytes, and the action of Fasudil was time-dependent and concentration-related. The rapid stellation of astrocytes (glial fibrillary acidic protein immunocytochemistry) induced by Fasudil was accompanied by reduced phalloidin staining of F-actin and increased V(max) for [(3)H]-D-Asp uptake. Immunoblotting after biotinylation demonstrated that Fasudil increased the expression of EAAT1 and EAAT2 on the cell surface. Immunocytochemistry indicated that Fasudil induced prominent labelling of astrocytic processes by EAAT1/2.Conclusion and Implications: These data show for the first time that ROCK plays a major role in determining the cell surface expression of EAAT1/2, providing new evidence for an association between transporter function and astrocytic phenotype. ROCK inhibitors, via the actin cytoskeleton, effect a consequent elevation of glutamate transporter function - this activity profile may contribute to their beneficial actions in neuropathologies. [ABSTRACT FROM AUTHOR]

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit-related protein (IGRP) (Ebert et al., Diabetes 48:543-551, 1999). To begin to investigate the molecular basis for the islet-specific expression of the IGRP gene, a series of truncated IGRP-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into the islet-derived mouse betaTC-3 and hamster insulinoma tumor cell lines. In both cell lines, basal fusion gene expression decreased upon progressive deletion of the IGRP promoter sequence between -306 and -66, indicating that multiple promoter regions are required for maximal IGRP-CAT expression. The ligation-mediated polymerase chain reaction footprinting technique was then used to compare trans-acting factor binding to the IGRP promoter in situ in betaTC-3 cells, which express the endogenous IGRP gene, and adrenocortical Y1 cells, which do not. Multiple trans-acting factor binding sites were selectively identified in betaTC-3 cells that correlate with regions of the IGRP promoter identified as being required for basal IGRP-CAT fusion gene expression. The data suggest that hepatocyte nuclear factor 3 may be important for basal IGRP gene expression, as it is for glucagon, GLUT2, and Pdx-1 gene expression. In addition, binding sites for several trans-acting factors not previously associated with islet gene expression, as well as binding sites for potentially novel proteins, were identified. [ABSTRACT FROM AUTHOR]

In liver and kidney, the terminal step in the gluconeogenic pathway is catalyzed by glucose-6-phosphatase (G-6-Pase). This enzyme is actually a multicomponent system, the catalytic subunit of which was recently cloned. Numerous reports have also described the presence of G-6-Pase activity in islets, although the role of G-6-Pase in this tissue is unclear. Arden and associates have described the cloning of a novel cDNA that encodes an islet-specific G-6-Pase catalytic subunit-related protein (IGRP) (Arden SD, Zahn T, Steegers S, Webb S, Bergman B, O'Brien RM, Hutton JC: Molecular cloning of a pancreatic islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP). Diabetes 48:531-542, 1999). We screened a mouse BAC library with this cDNA to isolate the IGRP gene, which spans approximately 8 kbp of genomic DNA. The exon/intron structure of the IGRP gene has been mapped and, as with the gene encoding the liver/kidney G-6-Pase catalytic subunit, it is composed of five exons. The sizes of these exons are 254 (I), 110 (II), 112 (III), 116 (IV), and 1284 (V) bp, similar to those of the G-6-Pase catalytic subunit gene. Two interspecific backcross DNA mapping panels were used to unambiguously localize the IGRP gene (map symbol G6pc-rs) to the proximal portion of mouse chromosome 2. The IGRP gene transcription start site was mapped by primer extension analysis, and the activity of the IGRP gene promoter was analyzed in both the islet-derived HIT cell line and the liver-derived HepG2 cell line. The IGRP and G-6-Pase catalytic subunit gene promoters show a reciprocal pattern of activity, with the IGRP promoter being approximately 150-fold more active than the G-6-Pase promoter in HIT cells. [ABSTRACT FROM AUTHOR]