ACTIVIN RECEPTOR MESSENGER-RNA EXPRESSION BY NEURONS OF THE AVIAN CILIARY GANGLION

Previous studies have suggested that activin may serve as a neurodiffe rentiation factor regulating somatostatin expression in neurons of the avian ciliary ganglion (CG), As one aspect of examining the role of a ctivin in CG development, we inquired whether any of the known activin receptors are expressed by developing CG neurons in vivo. In addition , we examined whether activin A mRNA is expressed in the choroid layer and iris of the chicken eye. Oligonucleotide primers were designed fo r the chicken activin receptor type IIA (cActR-IIA), type IIB (cActR-I IB), and activin A. In reverse-transcription - polymerase chain reacti on (rtPCR), an appropriately sized product was amplified from CG cDNA using primers to the cActR-IIA but not the cActR-IIB, Sequencing confi rmed the identity of the PCR product as a fragment of the cActR-IIA. I t thus appears that mRNA for the type IIA but not the type IIB activin receptor is expressed in the chicken CG, An antisense strand digoxige nin-labeled riboprobe complimentary to a 358-bp portion of the cActR-I IA kinase region hybridized to cells within cryostat sections of embry onic CG, From E6.5-E18, hybridization of this probe appears to be spec ific for cells with a neuronal morphology, Using rtPCR with activin A- specific primers we detected activin mRNA in the choroid layer of E14 and E19 eyes, and from the iris at E14, Our results are consistent wit h a role for activin as a neurodifferentiation factor in vivo, and imp ly that within the CG, the cActR-IIA is specifically expressed by neur ons, and that activin A is expressed in the targets of these neurons. (C) 1997 John Wiley & Sons, Inc.