Contraction of an embryonic epithelium, the enveloping layer of the medaka (Oryzias latipes), a teleost

Abstract

The enveloping layer (EVL), a simple epithelium that forms the outer covering of the blastoderm of the teleost embryo, contracted in situ when it was exposed to the calcium ionophore A23187. This contraction was inhibited by cytochalasin D and occurred in a Ca2+-free medium. When the EVL was detached from the rest of the embryo, it contracted into a tight ball. Detached EVLs contracted fully in Na+-, K+-, SO;--, M?'-, or glucose-free medium but only partially in medium containing less than 10 pM free Ca2+. Contraction was inhibited by the polyvalent cations La3+, Ni2+, Co2+, and Mn2' but not by the "calcium antagonists" D 600, verapamil, nifedipine, or papaverine; it was only slightly inhibited by the "calcium antagonist" diltiazem. The contraction was inhibited by cytochalasin B (1 pgiml) and cytochalasin D (1 pgiml) but not by demecolcine (0.35 mM) or colchicine (1 mM). The effects of lowered free Ca2+ and the cytochalasins were reversible.The contraction of EVLs permeabilized by the detergent Brij 58 was ATP and Ca2+ dependent. In the presence of 5 mM MgATP, the EVLs contracted only when the medium contained at least 1 pM free Ca2+. Three other nucleotides-ITP, GTP, and CTP-also supported contraction but at a lower rate than ATP. The contraction of permeabiliwd EVLs was inhibited by cytochalasin B (1 pg/ml), N-ethylmaleimide (6 mM), but not by 10 pM vanadate.Dissociated cells of the EVL underwent circus movement, which was inhibited nearly completely by cytochalasin B, cytochalasin D, and La3+ and inhibited partially by Ni2+, &In2+, and Co2+. Although the EVLs contain acetylcholine (1.2 pmol/EYL), the amount did not change significantly during contraction. The cholinergic antagonists d-tubocurarine and atropine sulfate and the cholinergic agonist carbamylcholine had no effect on the contraction.We conclude that the contraction of detached EVLs is a n ATP-, Ca2+-dependent phenomenon and that part of the Ca2+ required for contraction enters the cytoplasm from the medium. Microtubules have no apparent role in the contraction, but microfilaments probably do. Acetylcholine apparently has no role in the contraction.During development, the morphogenesis of embryonic epithelia is due largely to coordinated asymmetric changes in the shape of the cells within them. Because these cells are joined to their neighbors via surface juncby microfilaments, which are concentrated in the part of the cell undergoing contraction and are aligned in the axis of contraction (Burnside, '73; Spooner, '75; Owaribe et al., '81

Calcium signalling during zebrafish embryonic development

“…The rhythmic calcium waves could be related to the propagating calcium waves that accompany the rhythmic contraction of the stellate layer of medaka. (53)(54)(55) In the case of zebrafish, however, the pacemaker region generating these waves becomes established in the embryonic shield at the dorsal midline of the blastoderm margin, whereas in medaka the equivalent region is located on the opposite side of the embryo. (54) In addition, the period when the rhythmic waves occur in zebrafish overlaps with comparable stages of Xenopus development in which repeated calcium pulses and, possibly, waves were reported from dissociated neural plate cells.…”

Formation of the enveloping layer of the chum salmon egg in isotonic salt solutions

“…The importance of external Ca 2+ ions for cell-cell adhesion during embryonic development has been emphasized frequently in various animals (Herbst, 1900(Herbst, , 1904Yanagimachi, 1957;Takeichi & Okada, 1972;LeBlanc & Brick, 1981;Hyafil et al, 1981;Fluck et al, 1984). It is probable that the separation of blastomeres in 14·3% SRS is due to the absence of adhesion molecules on the cell surface and is related to relatively low contents of Ca 2+ ions in this solution (3·2 m).…”

In vivo time-lapse imaging in medaka – n-heptanol blocks contractile rhythmical movements

“…A thin layer of stellate-like cells beneath the EVL is responsible for the contractile movements (Cope et al, 1990). The contraction waves depend on extracellular calcium (Fluck et al, 1984) and can be inhibited by inorganic calcium antagonists (Fluck et al, 1984;Sguigna et al, 1988) or stimulated by the calcium ionophore A23187 (Fluck et al, 1984). More recently it was found that contraction waves are preceded by intercellular Ca 2þ waves and intracellular Ca 2þ oscillations within the stellate cell layer, indicating a role for gap junctional communication (Fluck et al, 1991;Simon and Cooper, 1995).…”