Developmental expression of LC3 alpha and beta: Absence of fibronectin or autophagy phenotype in LC3 beta knockout mice

Murine light chain 3 (LC3) exists as two isoforms, LC3 alpha and beta: LC3 beta is an RNA-binding protein that enhances fibronectin (FN) mRNA translation, and is also a marker of autophagy. We report embryonic expression patterns for LC3 alpha and LC3 beta, with some overlap but notable differences in the brain, and in tissues of non-neuronal origin. LC3 beta knockout (-/-) mice develop normally without a compensatory increase in LC3 alpha LC3 beta-/- embryonic fibroblasts (MEFs) exhibit reduced FN synthesis but maintain wild type (WT) levels of FN protein. No significant changes in proteins associated with FN turnover, i.e., caveolin-1, LRP-1, or matrix metalloproteinases were identified. Autophagosomes form in amino acid-starved LC3 beta-/-MEFs, and Caesarean-delivered pups survive as long as WT pups without an increase in LC3-related proteins linked to autophagy. These results suggest novel compensatory mechanisms for loss of LC3 beta, ensuring proper FN accumulation and autophagy during fetal and neonatal life.