Admp regulates tail bending by controlling the intercalation of the ventral epidermis through myosin phosphorylation

Chordate tailbud embryos have similar morphological features, including a bending tail. A recent study revealed that the actomyosin of the notochord changes the contractility and drive tail bending of the early Ciona tailbud embryo. Yet, the upstream regulator of tail bending remains unknown. In this study, we find that Admp regulates tail bending of Ciona mid-tailbud embryos. Anti-pSmad antibody signal was detected at the ventral midline tail epidermis. Admp knock-down embryo completely inhibited the ventral tail bending and reduced the number of the triangular-shaped cells, which has the apical accumulation of the myosin phosphorylation and inhibited specifically the cell-cell intercalation of the ventral epidermis. The degree of myosin phosphorylation of the ventral cells and tail bending were correlated. Finally, the laser cutter experiments demonstrated the myosin-phosphorylation-dependent tension of the ventral midline epidermis during tail bending. We conclude that Admp is an upstream regulator of the tail bending by controlling myosin phosphorylation and its localization of ventral epidermal cells. These data reveal a new aspect of the function of the Admp that might be evolutionarily conserved in bilaterian animals.Summary StatementAdmp is an upstream regulator of the bending of the tail in the tailbud embryo regulating tissue polarity of the ventral midline epidermis by phosphorylation of myosin.

Lack of influence of estrogen on myosin phosphorylation and post-tetanic potentiation in muscles from young adult C57BL mice

Estrogen influences myosin phosphorylation and post-tetanic potentiation in murine fast muscle. We tested the hypothesis that this influence is mediated by estrogen effects on skeletal myosin light chain kinase (skMLCK) activity. To this end, extensor digitorum longus muscles from female wildtype and skMLCK-absent (skMLCK−/−) mice were grouped as follows: ovariectomized with estrogen (E+), ovariectomized without estrogen (E–), sham surgery, and intact baseline. At 8 weeks of age, the ovariectomized groups were ovariectomized followed by implantation of either a 0.1 mg 17β-estradiol (E+) or placebo pellet (E–). Two weeks later, muscles were isolated and suspended in vitro (25° C) for determination of regulatory light chain phosphorylation and post-tetanic potentiation. Regulatory light chain phosphorylation was not different across conditions within either genotype although wildtype values were significantly greater than skMLCK−/− values. Consistent with this, the potentiation of concentric twitch force was similar between E+ and E– groups within each genotype but wildtype values were greater than skMLCK−/− values. However, unaltered estradiol levels following ovariectomy, likely due to previously underappreciated confounds of mouse age, development, and growth during estrogen supplementation, prevented direct testing of the hypothesis. Future studies should note the importance of estrous cycles and continuing physiological developments of young adult mice when working with ovarian hormones.