Muscular dystrophy by merosin deficiency decreases acetylcholinesterase activity in thymus of Lama2dy mice

Half of congenital muscular dystrophy cases arise from laminin alpha 2 (merosin) deficiency, and merosin-deficient mice (Lama2dy) exhibit a dystrophic phenotype. The abnormal development of thymus in Lama2dy mice, the occurrence of acetylcholinesterase (AChE) in the gland and the impaired distribution of AChE molecules in skeletal muscle of the mouse mutant prompted us to compare the levels of AChE mRNAs and enzyme species in thymus of control and Lama2dy mice. AChE activity in normal thymus (mean +/- SD 1.42 +/- 0.28 mu mol acetylthiocholine/h/mg protein, U/mg) was decreased by similar to 50% in dystrophic thymus (0.77 +/- 0.23 U/mg) (p = 0.007), whereas butyrylcholinesterase activity was little affected. RT-PCR assays revealed variable levels of R, H and T AChE mRNAs in thymus, bone marrow and spinal cord. Control thymus contained amphiphilic AChE dimers (G(2)(A), 64%) and monomers (G(1)(A), 19%), as well as hydrophilic tetramers (G(4)(H), 9%) and monomers (G(1)(H), 8%). The dimers consisted of glycosylphosphatidylinositol-anchored H subunits. Western blot assays with anti-AChE antibodies suggested the occurrence of inactive AChE in mouse thymus. Despite the decrease in AChE activity in Lama2dy thymus, no differences between thymuses from control and dystrophic mice were observed in the distribution of AChE forms, phosphatidylinositol-specific phospholipase C sensitivity, binding to lectins and size of AChE subunits.