Palate shelf movement in mouse embryo culture: Evidence for skeletal and smooth muscle contractility

Abstract

Previous biochemical and morphological studies have shown the presence of contractile proteins in mouse palates at the time of shelf movement. In order to determine whether the palatal contractile proteins function in shelf rotation, an embryo culture system in which palate shelves rotate has been developed. A J mouse fetuses with tongues removed (day 14.75) have been cultured close to the time that palatal shelves move in vivo and pharmacological agents added. The anterior end of the palate shelf completely rotated after overnight culture in the presence or absence of drugs. However, rotation of the posterior end of the palate was only partial. Agents that stimulate skeletal and smooth muscle contractility, pyridostigmine (2 × 10 −6–9 × 10 −5 M) and bethanechol (10 −10–10 −4 M), respectively, both enhanced posterior shelf rotation after overnight culture. Pyridostigmine (9 × 10 −5 M) increased posterior shelf rotation 74% over control; bethanechol (10 −4 M) 53%. Pyridostigmine effected an appreciable increase in anterior shelf movement within 60 min, while bethanechol stimulated posterior shelf rotation by 60% in that time. These results imply a cholinergic involvement in palate shelf rotation. Furthermore, contraction of “smooth muscle-like” structures previously found on the tongue side extending from top mid-palate to the posterior end may be involved in posterior palate shelf rotation; and contraction of skeletal muscle observed on the oral side posteriorly may aid both posterior and anterior shelf movement.