FGF-2 MESSENGER-RNA AND ITS ANTISENSE MESSAGE ARE EXPRESSED IN A DEVELOPMENTALLY SPECIFIC MANNER IN THE CHICK LIMB BUD AND MESONEPHROS

FGF-2 protein is present in the ectoderm and mesoderm of the developin g chick limb bud. Its importance has been shown by the ability of ecto pically applied FGF-2 to replace the apical ectodermal ridge, allowing complete outgrowth and subsequent pattern formation of the limb bud, The first goal of this study was to determine whether FGF-2 mRNA was p resent in the same ectodermal and mesodermal regions of the chick embr yo as FGF-2 protein, FGF-2 also has an antisense message that is conve rgently transcribed from the opposite DNA strand (Kimelman and Kirschn er [1989] Cell 59:687-696; Volk et al. [1989] EMBO J. 8:2983-3988), Th e second goal was to demonstrate the expression and distribution of th e antisense message, Using RNAse protection assays we detected a full length protected fragment that corresponds to chick embryo FGF-2 mRNA, and a partially protected fragment that corresponds to the antisense message. We used in situ hybridization to show that FGF-2 mRNA was pre sent in the ectoderm and subjacent mesoderm of the chick wing bud, FGF -2 mRNA was also present in body ectoderm and undifferentiated mesoder m throughout the embryo, and in muscle cells, dorsal neural tube, and mesonephros. In situ hybridization also revealed evidence for the pres ence of the natural antisense message in the embryo in most, but not a ll, of the same regions as the FGF-2 mRNA. FGF-2 mRNA and its antisens e message colocalized in undifferentiated limb mesoderm; however, anti sense message was not detected in differentiated muscle or cartilage. It is important to note that FGF-2 mRNA was always present in the meso nephros but that the antisense message was never observed in the meson ephros, thereby providing an internal control for non-specific signal, Although little is known about its function, Kimelman and Kirschner ( [1989] Cell 59: 687-696) proposed that the antisense message may incre ase turnover of FGF-2 mRNA. When we compared the in situ hybridization data of both mRNAs with levels of FGF-2 protein (Savage et al. [1994] Dev. Dyn. 198:159-170), interesting tissue specific patterns emerged that support this hypothesis. (C) 1995 Wiley-Liss, Inc.