Differentiation-induced mRNA synthesis by 3T3-L1 adipocytes: cDNA cloning and identification of a myelin P2-like mRNA

Differentiation of 3T3-L1 preadipocytes is accompanied by the expression of adipocyte-specific proteins. To study the basis of this differential expression a cDNA library was constructed with mRNA from 3T3-L1 adipocytes. Clones representing differentiation-induced mRNAs were identified using a mixzed probe (³²P-dif/³H-undif) hybridization screen with confirmation by Northern analysis. One clone, pAL422, contains a 672 bp insert that hybridizes to a ~ 600-base mRNA detectable only in differentiated cells. The sequence of this insert contains a long open reading frame that could code for a 132 amino acid, 14.6 kDa, protein (P422). The insert also contains a 43 bp 5'-untranslated region, a 172 bp 3'-untranslated region, and a 41 bp poly(a) tail. P422 shares 69% and 64% homology with myelin P2 proteins from rabbit and bovine peripheral nerve and 30% and 23% homology with fatty acid binding proteins of rat intestine and liver, respectively. mRNA, hybrid-selected by pAL422, directs the in vitro translation of a 13 kDa protein immunoprecipitable by anti-myelin P2 antibody. These results suggest that P422 is a structural, and perhaps functional, analog of myelin P2, and that adipocyte P422 and myelin P2 may be intracellular lipid carriers.