Actin bundles on the right side in the caudal part of the heart tube play a role in dextro-looping in the embryonic chick heart

Abstract

The role of actin bundles on the heart looping of chick embryos was examined by using cytochalasin B, which binds to the barbed end of actin filaments and inhibits association of the subunits. It was applied to embryos cultured according to New's method. Looping did not occur when cytochalasin B was applied diffusely in the medium. Further, we disorganized actin bundles in a limited part of the heart tube to examine the role of actin bundles in each part in asymmetry formation. A small crystal of cytochalasin B was applied to the caudal part of the heart tube on either the left or right side. The disorganization of actin bundles on the left side resulted in the right-bending of the heart, an initial sign of dextro-looping (normal pattern), and right side disorganization resulted in left-bending. We suggest that actin bundles on the right side of the caudal part of a heart tube generate tension and cause dextro-looping. Embryos whose hearts bent to the right rotated their heads to the right, and embryos with left-bent-hearts rotated their heads to the left. The rotation of the heart tube may therefore decide in which direction the body axis rotates.

Cardiac looping in experimental conditions: Effects of extraembryonic forces

“…Lepori (1967) and Castro-Quezada et al (1972), although disagreeing on details, proposed that the splanchnopleura cut results in a shift of the anterior intestinal portal to the opposite side of the cut, and the same thing happens later with the looped heart. On the other hand, Itasaki et al (1991) proposed that after rightside dissection, the splanchnopleura contracts to the left and pulls the heart toward the left side through its attachment to the ventral mesocardium at HH stage 9.…”

“…The bending component likely is a process intrinsic to the heart (Butler, 1952;Manning and McLachlan, 1990). The rightward rotation also may have an intrinsic component (Itasaki et al, 1991), but there are at least two possible sources of external forces that can influence the rotational component. First, the heart is restricted ventrally by an extraembryonic membrane, the splanchnopleura, which can push against the heart (Patten, 1922).…”

Cellular nonmuscle myosins NMHC‐IIA and NMHC‐IIB and vertebrate heart looping

“…Actin is a major component of looping (Manasek et al, 1972;Manasek, 1976b;Itasaki et al, 1991;Latacha et al, 2005). Development of actin filaments considerably differ in inner and outer myocardial cell layers (Shiraishi et al, 1992).…”

Blood flow through the embryonic heart outflow tract during cardiac looping in HH13–HH18 chicken embryos

“…Various hypotheses of mechanical looping mechanisms have been proposed, where experiments show that several redundant mechanisms are likely involved [17]. These include compressive axial forces as the heart tube lengthens [18], differential growth on either side of the tube [19], active cell shape change [14], cytoskeletal contractions [20] and extrinsic forces from neighbouring tissues [21]. Forces exerted by increasing haemodynamic load during the looping period are likely involved in the structural formation.…”