Figure 6. Changing amnion-serosa interactions during Tribolium extraembryonic morphogenesis.

Schematics are sagittal, with anterior left and dorsal up (A,C–E), or transverse with dorsal up (B), illustrating: initial separation during formation of the amnion and serosa as distinct epithelial covers (A), relative rotation in many embryos (B: shown at the position of the dashed line in A, see also Figure 6—figure supplement 1), EE apposition at the retracted germband stage (C), the successive stages of EE tissue withdrawal (D), and final tissue structure during degeneration at the dorsal organ stage (E, see also Figure 6—figure supplement 2). Amnion-serosa apposition persists during withdrawal morphogenesis (D), which involves EE tissue rupture (starburst), curling over of the resulting tissue edge as it everts (shown for the anterior-dorsal edge), and early serosal compaction as the EE edges fold medially. Abbreviations as in previous figures.

DOI: http://dx.doi.org/10.7554/eLife.13834.014

Figure 6—figure supplement 1. Frequency of embryonic longitudinal rotation during development.

(A) Sample sizes and film durations (blue bars) relative to landmark developmental stages (yellow bars: SW, serosal window closure; GBE, germband extension complete; SR, serosal rupture; staging as in Koelzer et al. (2014)). Embryos were analyzed from multiple time-lapse data sets of at least 15.75-hr duration at 30°C, recorded with an inverted DeltaVision RT (Applied Precision) microscope. Pooled data included embryos in the nGFP and various enhancer trap backgrounds (G04609-heart, G12424-serosa, KT650-serosa, HC079-amnion), including heterozygote crosses of HC079 with each of G04609, G12424, and nGFP. (Background autofluorescence was sufficient for scoring early development in the absence of specific GFP signal.) 'Frequency by stage' refers to the beginning of rotation; all embryos beginning during (16%) or after (41%) the SW stage completed rotation before the GBE stage. Rarely, a moderate degree of rotation occurred during dorsal closure (4%). (B). Chi-square statistics for specified comparisons. For significant results, text color-coding indicates the nature of the interaction. Longitudinal rotation ranged from approximately 20 to 100 degrees, with two-thirds of embryos rotating approximately 90°. Embryos laying on their dorsal or ventral surface ('poles') were more likely (69%) to rotate 90°, while embryos in lateral aspect (85%) tended to only rotate 45°. While overall there was no bias in direction of rotation, embryos initially laying on their right sides tended to rotate anticlockwise (70%) while embryos on their left sides rotated clockwise (78%). Direction of rotation was from the perspective of the embryo’s posterior (i.e., clockwise is right, anticlockwise is left). These directional biases are applicable across the full range from ventral-lateral through dorsal-lateral, such that rotation tended to result in more strictly lateral final orientations (64%). Meanwhile, most non-rotating embryos began in a lateral orientation (89%). (C) Pie charts representing the eight 45°-sectors of the egg circumference (D, dorsal; DL-L and -R, dorsal-lateral-left and -right; L-L and -R, lateral-left and -right; VL-L and -R, ventral-lateral-left and -right; V, ventral), color-coded for frequency of occurrence according to the heat map.

DOI: http://dx.doi.org/10.7554/eLife.13834.015

Figure 6—figure supplement 2. Separation during degeneration: the amnion and serosa resolve into two distinct dorsal organ structures.

Images are dorsal (A,A1,B1) or lateral (B,B2,C), with anterior up (A,B,B2,C), or upper-left (A1,B1), shown as maximum intensity projections (A,A1,B,B1) or sagittal optical sections (B2,C). Tissue-specific EGFP labels two distinct dorsal organ structures, each characterized by apical F-actin enrichment around a hollow center or cleft (arrow: amniotic; double-headed arrow: serosal). Scale bars are 100 µm (A,B) and 25 µm (A1,B1,B2). After the stage shown here, the two dorsal organs will separate: the serosa remains medial, while the amniotic dorsal organ migrates anteriorly to a position behind the head before undergoing final degeneration (Panfilio et al., 2013).

DOI: http://dx.doi.org/10.7554/eLife.13834.016