Does Differential Receptor Distribution Underlie Variable Responses to a Neuropeptide in the Lobster Cardiac System?

Central pattern generators produce rhythmic behaviors independently of sensory input; however, their outputs can be modulated by neuropeptides, thereby allowing for functional flexibility. We investigated the effects of C-type allatostatins (AST-C) on the cardiac ganglion (CG), which is the central pattern generator that controls the heart of the American lobster, Homarus americanus, to identify the biological mechanism underlying the significant variability in individual responses to AST-C. We proposed that the presence of multiple receptors, and thus differential receptor distribution, was at least partly responsible for this observed variability. Using transcriptome mining and PCR-based cloning, we identified four AST-C receptors (ASTCRs) in the CG; we then characterized their cellular localization, binding potential, and functional activation. Only two of the four receptors, ASTCR1 and ASTCR2, were fully functional GPCRs that targeted to the cell surface and were activated by AST-C peptides in our insect cell expression system. All four, however, were amplified from CG cDNAs. Following the confirmation of ASTCR expression, we used physiological and bioinformatic techniques to correlate receptor expression with cardiac responses to AST-C across individuals. Expression of ASTCR1 in the CG showed a negative correlation with increasing contraction amplitude in response to AST-C perfusion through the lobster heart, suggesting that the differential expression of ASTCRs within the CG is partly responsible for the specific physiological response to AST-C exhibited by a given individual lobster.

COPI complex isoforms are required for the early acceptance of compatible pollen grains in Arabidopsis thaliana.

The Coat Protein I (COPI) complex is a seven-subunit coatomer complex consisting of the α, ß, ß', γ, δ, ε, and ζ proteins. In Arabidopsis thaliana, COPI is required for retrograde transport from the Golgi to the endoplasmic reticulum, Golgi maintenance, and cell plate formation. During compatible pollination, vesicle recruitment to the pollen contact point is required for pollen hydration and pollen tube penetration. Here, to identify other aspects of trafficking involved in the acceptance of compatible pollen by stigmatic papillae and to determine their roles in compatible pollination, we characterized knockout lines of several isoforms of the COPI complex, including α1-COP, γ-COP, and ε-COP. Specifically, we characterized pollen grain adherence, pollen tube penetration, and seed set in the mutants. Of the mutant lines examined, α1-cop had the most severe phenotypes, including altered compatible pollen grain adherence and tube germination and reduced seed set, whereas the other lines had milder phenotypes but visibly retarded compatible pollen acceptance. This is the first study demonstrating that COPI complex subunits are required for the acceptance of compatible pollen.