Fig. 2

Fluorescent in situ hybridization showing the expression of myosin heavy chain mRNAs at different stages of Botryllus schlosseri life cycle. a Expression of Myh1 (yellow) along the striated muscle in the larval tail. b Myh3 expression along muscle circular (oral and atrial siphons) and longitudinal muscle fibers in the oozooid body wall. c Expression of Myh2 in the heart of the adult oozooid. d Myh3 expression in the body wall of a blastozooid: circular and longitudinal fibers. b–d Arrowheads indicating the circular muscles around the oral siphon, the longitudinal body muscles and the intersiphonal muscles. e Myh2 expression in the heart of an adult blastozooid. Gene names are indicated in the lower left corner of the pictures in yellow. Arrowheads point circular and longitudinal fibers. Blue nuclei: Hoechst staining. Scale bar: 50 μm. f Schematic drawing of the body musculature of a colony in stage C1. Adult, a primary bud, and a secondary bud are embedded in common tunic. At stage C1 adult and primary bud, the muscle fibers are developed and both are able to contract. The body wall musculature consists of circular muscles around the oral and atrial siphon, longitudinal muscles, and a band of intersiphonal muscles, connecting the two siphons. The heart lies to the ventral and right side of the zooid body