The actomyosin cytoskeleton of amoebae of the cellular slime molds acrasis rosea and protostelium mycophaga: structure, biochemical properties, and function

In amoebae of the cellular slime molds (mycetozoans) Acrasis rosea and Protostelium mycophaga, bundles of F-actin radiate from the endoplasm-ectoplasm interface into the pseudopodia, where G-actin is also located. We conclude that these actin bundles form a core scaffold driving pseudopod extension which is subsequently completed by filling with a more loosely organized meshwork of F-actin. Some bipolar, elongate amoebae of A. rosea also contained long bundles of F-actin that traverse the cells lengthwise and remotely resemble stress fibers. Rodlets of F-actin were scattered in the body of amoebae of A. rosea or formed star-shaped or polygonal complexes near or around contractile vacuoles, where they may play a role in contraction. In total protein extracts analyzed by SDS-PAGE and immunoblots the actins migrated like the rabbit skeletal muscle control. The relative proportion of actin in total protein extracts was 7.9% for A. rosea and 34.5% for P. mycophaga. We detected four or five isoactins in extracts of both species and we determined that the genome of each species contains approximately six actin genes. Whether they are all expressed or if posttranslational modifications occur remains to be determined. Myosin II was enriched in actomyosin extracts; its Mr was 187.8 kDa for A. rosea and 220.7 kDa for P. mycophaga. Cell models ("ghosts") contracted upon the addition of ATP. We conclude that amoebae of A. rosea and P. mycophaga, although behaving differently from those of Dictyostelium discoideum, contain the basic repertoire of molecules that enable pseudopod extension by actin polymerization and ATP-induced contraction of the cell cortex. Copyright 1998 Academic Press.     

Circadian expression of steroidogenic cytochromes P450 in the mouse adrenal gland--involvement of cAMP-responsive element modulator in epigenetic regulation of Cyp17a1

The cytochrome P450 (CYP) genes Cyp51, Cyp11a1, Cyp17a1, Cyb11b1, Cyp11b2 and Cyp21a1 are involved in the adrenal production of corticosteroids, whose circulating levels are circadian. cAMP signaling plays an important role in adrenal steroidogenesis. By using cAMP responsive element modulator (Crem) knockout mice, we show that CREM isoforms contribute to circadian expression of steroidogenic CYPs in the mouse adrenal gland. Most striking was the CREM-dependent hypomethylation of the Cyp17a1 promoter at zeitgeber time 12, which resulted in higher Cyp17a1 mRNA and protein expression in the knockout adrenal glands. The data indicate that products of the Crem gene control the epigenetic repression of Cyp17 in mouse adrenal glands.