Alterations in the relative amounts of specific mRNA species in the developing human brain in Down's syndrome

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Abstract
Total cellular poly(A)+ RNA was prepared after guanidinium thiocyanate extraction of frozen brain tissue from age-matched normal and Down''s syndrome (trisomy 21) human fetuses. Poly(A)+ RNA populations were analyzed by translation in vitro, followed by 2-dimensional gel analysis by using both isoelectric focusing (ISODALT system) and non-equilibrium pH-gradient electrophoresis (BASODALT system) as the 1st-dimension separation. The relative concentrations of poly(A)+ RNA species coding for 7 translation products were significantly altered in Down''s syndrome, as determined by both visual comparisons of translation-product fluorograms from normal and Down''s syndrome samples and by quantitative radioactivity determination of individual translation products. The relative concentrations of mRNA species coding for 2 proteins (68 kDa [kilodalton] and 49 kDa) were increased in Down''s syndrome and may represent genes located on chromosome 21. The relative concentrations of mRNA species coding for 5 proteins (37 kDa, 35 kDa, 24.5 kDa, 23 kDa) were decreased in Down''s syndrome, these probably representing secondary effects of the trisomy. Six Down''s syndrome-linked translation products (49 kDa, 37 kDa, 33 kDa, 25.5 kDa, 24.5 kDa, 23 kDa) did not migrate with appreciable amounts of cellular proteins on 2-dimensional gels and hence may represent either proteins of high turnover rates or those that are post-translationally modified in vivo. One translation product (68 kDa) comigrated with a major cellular protein species, which was identified as a 68 kDa microtubule-associated protein by limited peptide mapping. The significance of these changes is discussed in relation to the mechanisms whereby the Down''s syndrome phenotype is expressed in the human brain.