CLONING OF TROPOMODULIN CDNA AND LOCALIZATION OF GENE TRANSCRIPTS DURING MOUSE EMBRYOGENESIS

Tropomodulin (Tmod) is a tropomyosin-binding protein involved in the s tructuring of actin filaments. This report describes Tmod expression i n distinct patterns during embryonic development in a wider variety of adult and embryonic vertebrate tissues than previously reported. Iden tical Tmod cDNAs were cloned from mouse brain, skeletal muscle, heart, and hematopoeitic cells. Genomic blotting demonstrates that Tmod is e ncoded by a single gene, which has a 1077-bp open reading frame that i s highly homologous to that of the human erythrocyte. The spatial and temporal expression of the Tmod gene was examined during mouse embryog enesis using in situ hybridization. Tmod mRNA is present by 9.5 days p ostcoitum (p.c.) in the developing rostral somites, coincident with ex pression of contractile protein genes in myotomes, suggesting that Tmo d may play an important role in sarcomeric thin filament organization in skeletal muscle. While the expression of Tmod mRNA in cardiac muscl e is earlier than that in skeletal muscle, its appearance in the heart also coincides with the expression of genes for thin filament protein s and correlates with initial myocardial contractions at 8.0 days p.c. Tmod mRNA is not detected in developing smooth muscle of the gut, but Tmod mRNA is expressed in hematopoeitic cells in yolk sac and develop ing liver. The sensory ganglia and epithelia of the inner ear express Tmod mRNA as do other sensory neurons such as those in the olfactory e pithelium. Expression levels in the brain are much lower prenatally th an postnatally. These findings show that Tmod expression in many cell types is developmentally regulated, suggesting that the interaction of actin filaments with this tropomyosin binding protein is an important process in tissue and cell differentiation. (C) 1995 Academic Press, Inc.