CAR2, a prestalk cAMP receptor required for normal tip formation and late development of Dictyostelium discoideum.

Abstract

Extracellular cAMP serves as a primary signaling molecule to regulate the development of Dictyostelium discoideum. It is required for chemotaxis, aggregation, cytodifferentiation, and morphogenetic movement. The receptors for cAMP are members of the family of cell-surface receptors that are linked to G proteins and characterized by seven putative transmembrane domains. Previously, we have isolated the gene for the cAMP receptor subtype 1 (CAR1) from Dictyostelium and suggested that several genes related to CAR1 were present in the genome. Here, we describe a family of cAMP receptor genes of Dictyostelium and the isolation and function of the gene for the cAMP receptor subtype 2, CAR2. CAR2 is structurally similar to CAR1. Overall, their transmembrane and loop domains are -75% identical in amino acid sequence; however, their carboxyl termini are quite dissimilar; CAR2 possesses homopolymeric runs of histidines and asparagines that are absent from the corresponding region in CAR1. Although CAR1 is maximally expressed during the early stages of development, CAR2 is expressed only after cells have aggregated and, then, preferentially in prestalk cells. Transgenic Dictyostelium that have had their wild-type CAR2 gene replaced by a defective copy using homologous recombination proceed through early development but are detained at the tight mound stage. CAR2 may be required for cAMP-directed sorting of prestalk cells during pattern formation within the aggregation mound. Furthermore, although prestalk genes are expressed normally in aggregates that lack CAR2, they exhibit an enhanced expression of prespore-specific mRNA. Previously, we had shown that there was a requirement for CAR1 during early development. The present results demonstrate that the multiple responses of Dictyostelium to cAMP are regulated by distinct cAMP receptors that are encoded by unique genes.

Allorecognition, via TgrB1 and TgrC1, mediates the transition from unicellularity to multicellularity in the social amoebae Dictyostelium discoideum

“…These observations are inconsistent with the regulation of cell motility by soluble cAMP signaling. So, even though signaling through the cAMP receptor cAR2 is required for development at this time (Saxe et al, 1993), the detection of cAMP signals through cAR2 does not appear to trigger the coordinated migration of cells. In addition, extracellular cAMP signaling can be bypassed in aggregation-stage adenylyl cyclase (ACA) mutants by activating PKA and those cells display coordinated cell movement and cell differentiation, and carry out tissue morphogenesis (Wang and Kuspa, 1997;Rappel et al, 1999).…”

LagC is required for cell-cell interactions that are essential for cell-type differentiation in Dictyostelium.

“…Null mutations in genes involved in pulsatile cAMP signaling such as cAR1, Ga2, ACA, and PDE all lead to an aggregationminus phenotype (Kumagai et al 1989;Sun and Devreotes 1991;Franke and Kessin 1992;Pitt et al 1992). Mutations that affect cAMP-mediated processes during the aggregate stage, such as PDE overexpression or car2 null mutations, arrest development at the tight aggregate stage, after the induction of cell-type-specific gene expression (Traynor et al 1992;Saxe et al 1993). The LagC protein acts between these two phases of cAMP-directed development.…”

Identification and Characterization of a Novel α-Kinase with a von Willebrand Factor A-like Motif Localized to the Contractile Vacuole and Golgi Complex inDictyostelium discoideum

“…Using synthesized cDNA as template, PCR amplifications were performed with VwkA-specific primers [5Ј-CAACAGGTA-AACAACGTAGTGAACGTG-3Ј] and vWFA-AS(4928-03) [5Ј-CCAGGTTTAC-CAAGGTTACAACTTCC-3Ј]. As controls, PCR was performed on the same template samples with primers specific to the developmentally induced gene Car2 (Saxe et al, 1993) and the constitutively expressed gene IG7 (Nagasaki et al, 2002), by using primers as follows: …”