Denegre JM and Danilchik MV (1993), Deep cytoplasmic rearrangements in axis-respeci...

XB-ART-22044

Dev Biol 1993 Nov 01;1601:157-64. doi: 10.1006/dbio.1993.1294.

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Deep cytoplasmic rearrangements in axis-respecified Xenopus embryos.

Denegre JM , Danilchik MV .

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In fertilized eggs of the frog Xenopus, the vegetal yolk mass rotates away from the future dorsal side (J. P. Vincent and J. Gerhart, 1987, Dev. Biol. 123, 526-539), and a major rearrangement of the deep animal hemisphere cytoplasm produces a characteristic swirl in the prospective dorsal side (M. V. Danilchik and J. M. Denegre, 1991, Development 111, 845-856). The relationship between this swirl and determination of the dorsal-ventral axis was further investigated by attempting to experimentally separate the positions of the swirl and the dorsal-ventral axis. Eggs were obliquely oriented in the gravity field to respecify the direction of yolk mass rotation and the position of the dorsal-ventral axis. When yolk mass rotation occurred in the absence of a sperm, as in activated eggs, a swirl pattern formed on the side away from which the yolk mass had rotated. In fertilized eggs tipped with the sperm entry point (SEP) down or to the side, swirl patterns were always found to form on the side away from which the yolk mass was displaced. However, in eggs tipped SEP up, in which the yolk mass was forced to rotate away from the SEP, more complicated rearrangements were observed in addition to the rotation-oriented swirl. Because the direction of yolk mass rotation was found to be influenced by both gravity and the actual position of the SEP in obliquely oriented eggs (SEP to the side), such complicated rearrangement patterns may result from opposing forces generated by both yolk mass rotation and the expanding sperm aster. Thus, except in cases in which the influences of SEP position and unit gravity opposed each other, it was not possible to experimentally separate the position of the deep cytoplasmic swirl from the direction of yolk mass rotation, and therefore the position of the prospective dorsal side.

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Species referenced: Xenopus laevis
Genes referenced: tubb
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	FIG. 1. Diagram of off-axis tipping. Eggs were tipped, in the orientations shown, on the inverted confocal microscope. Bottom panels represent the view of yolk mass rotation from below. Arrows represent the direction of movement of yolk platelets.
	FIG. 2. Mid-sagittal section of a control egg, fi,;.ed at 0.85 NT. The direction of yolk mass rotation was to the left. The SEP is marked by the arrowhead. The prospective dorsal side and the swirl are to the right.
	FIG. 3. Off-axis-tipped eggs. All mid-sagittal sections are oriented with the direction of yolk mass rotation to the left. Arrowheads mark the SEP. (A) Mid-sagittal section of SEP-down egg. SEP is on the left and prospective dorsal is to the right. (B) Mid-sagittal section of SEP-ta-theside egg (plane of section is parallel with the direction of yolk mass rotation). Prospective dorsal is to the right and SEP is out of the plane of section. (C) Vertical section of egg in B (plane of section intersects the SEP meridian, 15Â° away from the plane of section in B). (D) Mid-sagittal section of SEP-up egg. Prospective dorsal and the SEP are to the right. (E) Mid-sagittal section of activated, off-axis-tipped egg. Prospective dorsal is to the right. (F) Mid-sagittal section of cold-shocked, SEP-up egg. Prospective dorsal and SEP are to the right.
	FIG. 4. Diagram of the direction of yolk mass rotation in eggs tipped SEP meridian to the side (top of diagram). Solid arrows trace the movements of individual yolk platelets. The dashed arrow indicates the direction of rotation expected if eggs had been tipped with SEP meridian up (see Fig. 1}.
	FIG. 5. The effect of cold on vegetal, cortical microtubules. Eggs were fixed and stained for immunofluorescent staining as described under Materials and Methods. Vegetal views are shown in hoth panels. (A) Control egg fixed at0.7 NT. {B) Egg cold s ho1~ked at 0.4 NT, fixed at 0.7 NT.