Figure 1.
MTs reorganize during THN migration.(A) 30-hpf embryo expressing GFP in the atoh1a-Gal4/UAS-system. Anatomical markers are shown. Scale bar, 100 µm. (B) THNs exhibit a bipolar morphology in phase 1 with a long extension contacting the URL (magenta arrow) and a unipolar morphology with a leading process (orange arrow) in phase 2. Dots indicate the nuclei. Trans-light image serves as tissue reference; cb is cerebellum. Scale bar, 10 µm. See also Video 1. (C) Left: Magnified from the magenta region indicated in B, turned by 90°. A phase 1 THN with bipolar morphology positioned between the URL and MHB with EB3-GFP signals emanating from the URL. Right: Magnified from the orange region indicated in B. A phase 2 THN, where EB3 signals originate near the nucleus. In the leading process, individual EB3-GFP comets are difficult to distinguish. Scale bar, 5 µm. (D–F) Cartoon images represent the morphology and tissue position of THNs migrating in different phases; arrow indicates the migration direction. Images of EB3 tracks represent examples from films of ∼2 min (phase 1), ∼17 min (intermediate phase), and ∼30 s (phase 2) duration from one (intermediate, phase 2) or several cells (phase 1). Scale bars, 5 µm. (D) In phase 1, MTs emanate from the distal rear of the THN, and EB3 tracks are mostly unipolar. (E) In intermediate phase, MTs extend in all directions. (F) In phase 2, MTs appear unorganized in the soma, and ∼25% of plus ends are directed into the leading process. (G) MT reorganization correlates with the position of the centrosome at the rear in phase 1 THNs. When the nucleus has reached the MHB, the centrosome moves toward the nucleus together with the retracting rear. Arrows indicate individual examples. Note that the images have been turned by 90°. Scale bar, 10 µm. (H) The centrosome occupies an unstable position near the nucleus in phase 2. Arrows indicate the centrosome. Scale bar, 10 µm. All elapsed time is given in minutes. Where tissue boundaries are indicated, the MHB is marked as a solid line and the URL as a dotted line.

MTs reorganize during THN migration. (A) 30-hpf embryo expressing GFP in the atoh1a-Gal4/UAS-system. Anatomical markers are shown. Scale bar, 100 µm. (B) THNs exhibit a bipolar morphology in phase 1 with a long extension contacting the URL (magenta arrow) and a unipolar morphology with a leading process (orange arrow) in phase 2. Dots indicate the nuclei. Trans-light image serves as tissue reference; cb is cerebellum. Scale bar, 10 µm. See also Video 1. (C) Left: Magnified from the magenta region indicated in B, turned by 90°. A phase 1 THN with bipolar morphology positioned between the URL and MHB with EB3-GFP signals emanating from the URL. Right: Magnified from the orange region indicated in B. A phase 2 THN, where EB3 signals originate near the nucleus. In the leading process, individual EB3-GFP comets are difficult to distinguish. Scale bar, 5 µm. (D–F) Cartoon images represent the morphology and tissue position of THNs migrating in different phases; arrow indicates the migration direction. Images of EB3 tracks represent examples from films of ∼2 min (phase 1), ∼17 min (intermediate phase), and ∼30 s (phase 2) duration from one (intermediate, phase 2) or several cells (phase 1). Scale bars, 5 µm. (D) In phase 1, MTs emanate from the distal rear of the THN, and EB3 tracks are mostly unipolar. (E) In intermediate phase, MTs extend in all directions. (F) In phase 2, MTs appear unorganized in the soma, and ∼25% of plus ends are directed into the leading process. (G) MT reorganization correlates with the position of the centrosome at the rear in phase 1 THNs. When the nucleus has reached the MHB, the centrosome moves toward the nucleus together with the retracting rear. Arrows indicate individual examples. Note that the images have been turned by 90°. Scale bar, 10 µm. (H) The centrosome occupies an unstable position near the nucleus in phase 2. Arrows indicate the centrosome. Scale bar, 10 µm. All elapsed time is given in minutes. Where tissue boundaries are indicated, the MHB is marked as a solid line and the URL as a dotted line.

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