Cloning and Tissue Specific Expression of the Axolotl Cellular Retinoic Acid Binding Protein

The CRABP gene encodes a cellular retinoic acid binding protein which is believed to mediate the teratogenic and pattern altering effects of retinoic acid (RA) on developing and regenerating systems. As a first step in examining the role of CRABP in transducing the effects of RA in the regenerating urodele limb, we have isolated with PCR three partial cDNAs which encode the axolotl (Ambystoma mexicanum) cellular retinoic acid binding protein (aCRABP) and analyzed its expression in various tissues by Northern analysis. Sequence analysis of the clones revealed a high degree of nucleotide and deduced amino acid homology with mammalian and avian CRABP I, showing the highest homology with mouse CRABP I (79% & 85%, respectively). The results of Northern analysis show that aCRABP I codes for a single μ 1.3 kb transcript. A strong signal is observed in the RNA of stage 40 axolotl embryos and larval brain, whereas a weaker signal is detected in the larval heart, and muscle-skin of limbs. No message is detected in larval spleen, liver, or several stages of limb regeneration blastemas. The absence of aCRABP I message in the limb regeneration blastema suggests that CRABP II or another isoform is responsible for the observed RA binding activity of these tissues.