The metazoan mitochondrial (mt) genome is typically a circular, double-stranded DNA molecule between 14 and 18 kb in size. This molecule encodes 37 genes: 13 protein genes, 2 ribosomal RNA genes, and 22 tRNA genes (Wolstenholme 1992). The order of these genes varies among metazoans (Boore 1999). The mt genomes of 14 insects have been completely sequenced. These include (1) seven flies (Diptera),

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The P element appears to be one of the most recently invaded transposons of D. melanogaster . To study the dynamics and long-term fate of P elements in natural populations of D. melanogaster , 472 isofemale lines newly collected from 27 localities of Japan were examined for the P element-associated characteristics (abilities to induce and repress of P element transposition) and genomic P element composition (size classes and their numbers). There was variation in the P elementrelated phenotypes among local populations, but genomic P composition did not correlate strongly with the phenotype of each line: full-size P and KP elements predominated in their genomes ( FP + KP predominance). Comparison with previous results suggests a stability in the P-M system in local populations over about 15 years. In some populations, phenotypic stability for particularly long times was found: for 30 years or more Q strains predominated in Hikone and Tanushimaru, P or Q strains around Inakadate, and M ' or Q strains around Tozukawa. There was no clear evidence of structural destruction underlying functional variation of P elements during this period. These results suggest that the current evolutionary status of P elements in the gene pool of D. melanogaster is not intermediary stage predicted by the original recent invasion hypothesis, and that several other factors such as the position effect play important roles.

We analyzed the genomic P elements of 57 wild-derived Drosophila melanogaster isofemale lines from Africa, Australia and Asia. All carried many P sequences per genome, and the full-size P and the internally deleted KP elements were very common or predominant in the populations. The genomic content of full-size P and KP elements does not correlate well with the P transposition-inducing and -repressing abilities of a line. Our results show that a large majority of type I repressor elements are full-size P elements, and almost all type II repressor elements are KP elements in the natural populations of D. melanogaster from these parts of the world.

Hypothalamo-neurohypophysial system (HNS) releases arginine vasopressin (AVP) and oxytocin (OXT) from axonal terminals of the neurohypophysis (NH) into blood circulation for controlling body fluid homeostasis and lactation. Chronic osmotic and suckling stimulations have been shown to cause neurovascular and neuroglial reconstruction in the NH of adult mammals and no study has been reported for vascular dynamics. The aim of this study was to elucidate the occurrence of continuous angiogenesis and growth factor-dependent neurovascular reconstruction in the NH of adult mice. Active proliferation of endothelial cells and oligodendrocyte progenitor cells (OPCs) was observed using the immunohistochemistry of bromodeoxyuridine and Ki-67. Vascular endothelial growth factor A (VEGFA) and VEGF receptor 2 (VEGFR2 (KDR)) were highly expressed at pituicytes and endothelial cells respectively. Moreover, prominent expression of platelet-derived growth factor B (PDGFB) and PDGF receptor beta was observed at OXT-containing axonal terminals and pericytes respectively. Administration of the selective tyrosine kinase inhibitor AZD2171 for VEGFRs and STI571 for PDGFRs significantly decreased proliferation of endothelial cells and OPCs. Moreover, AZD2171 treatment decreased vascular density by facilitating apoptosis of endothelial cells and the withdrawal of its treatment led to remarkable rebound proliferation of endothelial cells, so that vascular density rapidly returned to normal levels. AZD2171 decreased the density of both AVP-and OXT-containing axonal terminals, whereas STI571 selectively decreased the density of AVP-containing ones. Thus, this study demonstrates that the signaling pathways of VEGF and PDGF are crucial mediators for determining proliferation of endothelial cells and OPCs and the density of AVP-and OXT-containing axonal terminals in the HNS.