No abstract

This suggests that adaptation results from alterations in components which are unique to the folic acid and cAMP signal transduction pathways, for instance, the cell surface receptors for either of these compounds. cAMP RECEPTORS IN D. DISCOIDEUM

When plus and minus mating type gametes of Chlamydomonas eugametos were mixed, a rapid transient increase in the amount of CAMP was observed with a maximum at 20 s after the start of the sexual agglutination reaction. The transient increase only occurred within the cells and was also exhibited when cell suspensions of single mating type were presented with isolated flagella of the other mating type. Cyclic AMP-dependent protein kinase and cyclic AMP-phosphodiesterase activities were found in cell homogenates. Since the rise in CAMP concentration preceded all known morphological and physiological changes in the cells that prepare them for fusion, it might be a primary response, induced by sexual agglutination.

In 2004 a law was introduced in The Netherlands, which gives offspring conceived by semen or oocyte donation the right to know the identity of the donor. The law also regulates the provision of other information concerning the donor to the offspring, their parents or their general practitioner. With the introduction of this law, a choice has been made in which the wish of offspring prevails above others involved. Donors can no longer claim absolute anonymity; they are anonymous at the time of donation, but if a child aged > or =16 years requests information the donor may now be traced. During 15 years of debate on the abolition of donor anonymity the number of donors decreased by >70% and the number of semen banks by 50%. We describe the debate which led to the law, the characteristics of the law itself and note some of the probable and possible consequences for donor offspring, parents, donors and semen banks.

Extracellular cAMP induces the activation of adenylate cyclase in Dictyostelium discoideum cells. Conditions for both stimulation and inhibition of adenylate cyclase by guanine nucleotides in membranes are reported. Stimulation and inhbition were induced by GTP and non-hydrolysable guanosine triphosphates. GDP and non-hydrolysable guanosine diphosphates were antagonists. Stimulation was maximally twofold, required a cytosolic factor and was observed only at temperatures below 10 "C. An agonist of the CAMP-receptor-activated basal and GTP-stimulated adenylate cyclase 1.3-fold. Adenylate cyclase in mutant N7 could not be activated by cAMP in vivo; in vitro adenylate cyclase was activated by guanine nucleotides in the presence of the cytosolic factor of wild-type but of not mutant cells.Preincubation of membranes under phosphorylation conditions has been shown to alter the interaction between cAMP receptor and G protein [Van Haastert (1986) J. Biof. Chem. in the press]. These phosphorylation conditions converted stimulation to inhibition of adenylate cyclase by guanine nucleotides. Inhibition was maximally 30% and was not affected by the cytosolic factor involved in stimulation.In membranes obtained from cells that were treated with pertussis toxin, adenylate cyclase stimulation by guanine nucleotides was as in control cells, whereas inhibition by guanine nucleotides was lost. When cells were desensitized by exposure to cAMP agonists for 15 min, and adenylate cyclase was measured in isolated membranes, stimulation by guanine nucleotides was lost while inhibition was retained. These results suggest that Dictyostelium discoideum adenylate cyclase may be regulated by Gs-like and Gi-like activities, and that the action of Gs but not Gi is lost during desensitization in vivo and by phosphorylation conditions in vitro.Extracellular cAMP functions as an intercellular signal molecule in Dictyostelium discoideum, and is involved in chemotaxis [l], morphogenesis [2] and cell differentiation [3]. cAMP binds to highly specific cell-surface cAMP receptors, which activate several enzymes, including adenylate cyclase and guanylate cyclase (reviewed in [4-61). The cGMP produced remains largely intracellular and is probably involved in the chemotactic reaction [7-991. The cAMP produced is secreted [lo], and may trigger more distal cells, thus relaying the signal.The regulation of adenylate cyclase activity by cAMP in D. discoideum cells has been well characterized [ll -141. Enzyme activity increases at about 10-30 s after cAMP addition, reaches maximal activity after 1-2 min and then decays to prestimulation levels. The decay of adenylate cyclase activity occurs even when the cAMP concentration remains constant and proceeds with a half-life of 3 -4 min. This desensitization is reversible with a similar half-life period when cAMP is Leichtling et al. [20], who showed that a 42-kDa protein binds GTP and can be ADP-ribosylated by cholora toxin. In vertebrate cells G proteins mediate the signal from hormone receptor to adenylate cycl...