Cyclic AMP is an intracellular mediator ('second messenger') in the nervous and endocrine control of cellular function, regulating different processes in different cell types. Although evidence is incomplete, it seems that cyclic AMP enhances the calcium-mediated release of neurotransmitter in some neurones. A simple form of memory in the mollusc Aplysia is probably encoded as a cyclic AMP-induced enhancement of neurotransmission at certain synapses of the central nervous system. The possibility that cyclic AMP participates in learning mechanisms may be explored using genetic mutants. For this purpose the fruitfly Drosophila is suitable as it is genetically well characterized and can learn through olfaction, vision or taste. We show here that independent searches for mutations of olfactory learning and of cyclic AMP metabolism, and for mutations causing female infertility have each led to the same gene--the dunce gene. Our evidence indicates that the normal dunce gene may specify a cyclic AMP phosphodiesterase.

The final step in morphogenesis of the adult fly is wing maturation, a process not well understood at the cellular level due to the impermeable and refractive nature of cuticle synthesized some 30 h prior to eclosion from the pupal case. Advances in GFP technology now make it possible to visualize cells using fluorescence after cuticle synthesis is complete. We find that, between eclosion and wing expansion, the epithelia within the folded wing begin to delaminate from the cuticle and that delamination is complete when the wing has fully expanded. After expansion, epithelial cells lose contact with each other, adherens junctions are disrupted, and nuclei become pycnotic. The cells then change shape, elongate, and migrate from the wing into the thorax. During wing maturation, the Timp gene product, tissue inhibitor of metalloproteinases, and probably other components of an extracellular matrix are expressed that bond the dorsal and ventral cuticular surfaces of the wing following migration of the cells. These steps are dissected using the batone and Timp genes and ectopic expression of alphaPS integrin, inhibitors of Armadillo/beta-catenin nuclear activity and baculovirus caspase inhibitor p35. We conclude that an epithelial-mesenchymal transition is responsible for epithelial delamination and dissolution.

Ethanol has complex but similar effects on behavior in mammals and the fruit fly Drosophila melanogaster. In addition, genetic and pharmacological approaches have implicated the cAMP pathway in the regulation of ethanol-induced behaviors in both flies and rodents. Here we examine the neuroanatomical loci that modulate ethanol sensitivity in Drosophila by targeting the expression of an inhibitor of cAMP-dependent protein kinase (PKA) to specific regions in the fly's brain. Expression of the inhibitor in most brain regions or in muscle has no effect on behavior. In contrast, inhibition of PKA in a relatively small number of cells, possibly neurosecretory cells, in the fly's brain is sufficient to decrease sensitivity to the incoordinating effects of ethanol. Additional brain areas are, however, also involved. The mushroom bodies, brain structures where cAMP signaling is required for olfactory classical conditioning, are dispensable for the regulation of ethanol sensitivity. Finally, different behavioral effects of ethanol, motor incoordination and sedation, appear to be regulated by PKA function in distinct brain regions. We conclude that the regulation of ethanol-induced behaviors by PKA involves complex interactions among groups of cells that mediate either increased or reduced sensitivity to the acute intoxicating effects of ethanol.

The cyclic AMP and cyclic GMP phosphodiesterase activities present in flies of six mutant strains of the dunce gene and in the parent wild-type strains are characterized . All of the mutants exhibit aberrant cyclic AMP metabolism . The mutant strains dunce M14 , dunce M ", and dunce' appear to be amorphic, because they completely lack the CAMP-specific phosphodiesterase normally present in adult flies. These strains exhibit extremely high levels of CAMP . The mutant strains dunce', dunce', and duncec' are hypomorphic and exhibit reduced levels of the CAMP-specific phosphodiesterase . These strains exhibit less marked increases in CAMP content compared with the three amorphic strains . The dunce' strain possesses a residual enzyme activity that exhibits anomalous kinetics compared with those of the normal enzyme . The possibility that the dunce locus is the structural gene for the CAMP-specific phosphodiesterase is discussed.Adult flies of the species Drosophila melanogaster have two major forms of cyclic nucleotide phosphodiesterase . Form I phosphodiesterase will use either cyclic AMP or cyclic GMP as substrate; form II is specific for cyclic AMP (1) . The activity of form II enzyme is controlled in a dosage-dependent manner by chromomere 3D4 of the X chromosome (2) . Deletion of chromomere 3D4 produces an associated phenotype of female sterility (3) . This has made possible the identification of femalesterile mutations that influence form II activity (H. K . Salz, R. L. Davis, and J . A. Kiger, Jr., unpublished observations). Several mutants of D. melanogaster are known that show deficiency in learning or memory (4-6) . The first to be isolated is one named dunce (4). Whereas normal flies tend to avoid odorants after training in an apparatus that couples olfactory cues with electrical shock (7), dunce mutant flies are defective in associative avoidance and are classed as learning deficient . Recently, allelism between dunce mutations and the femalesterile mutations located at chromomere 3D4 was established (8) . The allele dunce' is a recessive female-sterile (8), permitting allelism to be determined with the female-steriles in 3D4 through complementation tests . Crude homogenates of flies homozygous for the dunce' or dunce' alleles were shown to have reduced capacity to hydrolyze cyclic AMP, and form II phoshodiesterase was virtually undetectable in homogenates of these mutant flies after velocity sedimentation in sucrose gradients (9) .

DNA methylation at CpG residues is closely associated with a number of biological processes during vertebrate development. Unlike the vertebrates, however, several invertebrate species, including the Drosophila, do not have apparent DNA methylation in their genomes. Nor have there been reports on a DNA (5-cytosine) methyltransferase (CpG MTase) found in these invertebrates. We now present evidence for two CpG MTase-like proteins expressed in Drosophila cells. One of these, DmMTR1, is a protein containing peptide epitopes immunologically related to the conserved motifs I and IV in the catalytic domain of the mammalian dnmt1. DmMTR1 has an apparent molecular mass of 220 kDa and, similar to mammalian dnmt1, it also interacts in vivo with the proliferating cell nuclear antigen. During interphase of the syncytial Drosophila embryos, the DmMTR1 molecules are located outside the nuclei, as is dnmt1 in the mouse blastocyst. However, DmMTR1 appears to be rapidly transported into, and then out of the nuclei again, as the embryos undergo mitotic waves. Immunofluorescent data indicate that DmMTR1 molecules ''paint'' the whole set of condensed Drosophila chromosomes throughout the mitotic phase, suggesting they may play an essential function in the cell-cycle regulated condensation of the Drosophila chromosomes. Through search in the genomic database, we also have identified a Drosophila polypeptide, DmMT2, that exhibits high sequence homology to the mammalian dnmt2 and the yeast CpG MTase homolog pmt1. The expression of DmMT2 appears to be developmentally regulated. We discuss the evolutionary and functional implications of the discovery of these two Drosophila proteins related to mammalian CpG MTases.epitope detection ͉ early embryo ͉ cell cycle ͉ chromatin structure ͉ database