Signal transduction by cAMP-dependent protein kinase A in Drosophila limb patterning

Abstract

Interaction between distinctly specified cells in adjacent compartments establishes organizing centres that control growth and specify cell fate in the developing limbs of Drosophila. Localized expression of the secreted Hedgehog protein (Hh) by cells in the posterior compartment induces expression of the secreted signalling molecules decapentaplegic (dpp) or wingless (wg) in nearby anterior cells. wg and dpp in turn organize spatial pattern in the wing and leg imaginal discs. The Hh signal is thought to act by antagonizing the ability of the patched (ptc) gene product to repress wg and dpp expression. Here we present evidence that removing activity of the gene encoding cyclic AMP-dependent protein kinase A (pka) is functionally equivalent to removing ptc activity or to providing cells with the Hh signal. These findings suggest that cyclic AMP-dependent protein kinase A is a component of the signal transduction pathway through which Hh and Ptc direct localized expression of dpp (or wg) and establish the compartment boundary organizer.

Accumulation in fetal muscle and localization to the neuromuscular junction of cAMP-dependent protein kinase A regulatory and catalytic subunits RI alpha and C alpha.

“…In particular, it will be critical to determine whether their appearance precedes myogenic differentiation, in which case, PKA could be involved in developmental decisions, or whether their expression occurs only later, implying a role in muscle maturation and/or physiology. In line with the first possibility, PKA has been demonstrated to play a key role in Drosophila and zebrafish embryos in the maintenance of repression of genes induced by hedgehog: abolition or inhibition of PKA leads to ectopic expression of target genes under the inducing influence of the hedgehog product (Li et al, 1995;Jiang and Struhl, 1995;Pan and Rubin, 1995;Lepage et al, 1995;Hammerschmidt et al, 1996). In addition, cAMP can interfere with sonic hedgehog induction of sclerotome markers (Fan et al, 1995).…”

“…In addition, a series of recent papers has implicated PKA in major developmental decisions in Drosophila (Lepage et al, 1995;Jiang and Struhl, 1995;Li et al, 1995;Pan and Rubin, 1995). It is therefore tempting to speculate that this kinase could be important during the course of development and of cell differentiation in mammals as well.…”

Increased Basal cAMP-dependent Protein Kinase Activity Inhibits the Formation of Mesoderm-derived Structures in the Developing Mouse Embryo

“…Homogenates were thawed on wet ice and kinase assays performed in triplicate in the presence and absence of 5 M cAMP with Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) as the substrate. Assays were also performed in the presence of 40 g/ml protein kinase inhibitor peptide- (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) to demonstrate that the kinase activity was PKA-specific (25). Bradford assays (Bio-Rad) were performed to determine protein concentration, and kinase activity was normalized to milligrams of protein.…”

Degrading Ci: who is Cul-pable?

“…Loss-of-function mutations in the catalytic subunit of PKA lead to constitutive Hh signaling (Jiang and Struhl 1995;Lepage et al 1995;Li et al 1995;Pan and Rubin 1995). Subsequent work indicated that PKA phosphorylates a C-terminal region of Ci at multiple Ser/Thr residues essential for its processing (Y.…”