Signalling mechanisms involving CAMP have a well-documented role in the coordination of multicellular development and differentiation leading to spore formation in the social amoeba, Dictyostelium discoideum. The involvement of CAMP in the poorly understood developmental stages of spore dormancy and germination have been investigated in this study. Dormant spores contained up to l l -f o l d more cAMP than nascent amoebae. The spore CAMP levels were not constant, but typically underwent a surge at 14-18 d when spores acquired the ability to germinate spontaneously. The high CAMP levels decreased only during successful spore germination, i.e. emergence of nascent amoebae. The temporal pattern of CAMP decrease was complex and unique to the method of spore activation, supporting our hypothesis that exogenously (e.g. heat) activated and autoactivated spores germinate by different mechanisms. During heat-induced activation, transcription of acg (a gene encoding adenylyl cyclase associated with germination) correlated well with spore CAMP content. Young wild-type spores, incapable of spontaneous germination, maintained a uniformly high CAMP level, and spore CAMP levels also remained high if germination was inhibited. When activated spores were deactivated by applying increased osmotic pressure, CAMP concentrations rose and ultimately levelled off a t the high levels typical of dormant spores. The correlation between high CAMP and failure to germinate was also evident when autoactivation was inhibited by the CAMP analogue, 8-bromo-CAMP. Also, spores from a strain (HTY217) with unrestrained protein kinase A activity were incapable of spontaneous germination. Overall, our experiments provide evidence for continued CAMP signalling in spores up to 18 d after sporulation and for linkages between elevated CAMP, spore deactivation and inhibition of spontaneous germination.

The life cycles of species of Hepatozoon that occur naturally in eastern garter snakes, Thamnophis sirtalis sirtalis, were studied in the mosquito Culex pipiens in various amphibians, including northern leopard frogs, bullfrogs, gray treefrogs, American toads, and blue-spotted salamanders, and in natricine snakes, including northern water snakes and northern brown snakes. Morphological features of the oocysts of two forms of Hepatozoon from various widely separated regions of Ontario differed with respect to the number of sporozoites per sporocyst and the diameter and shape of the oocyst. However, morphological and morphometric differences were not apparent in the cystic or merogonic stages in the vertebrate hosts. Cystic stages of these haemogregarines were found in the liver of all four species of anurans, but not in salamanders. These forms were transmitted experimentally to garter, water, and brown snakes, with gamonts appearing in erythrocytes 45 days after the snakes were fed infected anurans. A comparison of these forms of Hepatozoon with previously named species of ophidian haemogregarines from North America indicates that there are at least two, and likely more, species of Hepatozoon in Ontario.