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. 2021 Dec 23;10:e74336. doi: 10.7554/eLife.74336

Figure 6. POU-IV is necessary for maturation of hair cells in the sea anemone.

Confocal sections of oral tentacles in F2 pou-iv -/- Nematostella vectensis polyps, labeled with antibodies against tyrosinated ∂-tubulin (‘tyrTub’), minicollagen 3 (‘Ncol3’; Zenkert et al., 2011), mutant POU-IV (‘POU-IV(-)’), and/or Kaede fluorescent protein (‘pou-iv::kaede’). DNA fragmentation is labeled by terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL). Filamentous actin is labeled with phalloidin (Pha), and nuclei are labeled with DAPI (dapi). In all panels, the apical surface of the tentacular ectodermal epithelium is to the top. (A–C) Sections through developing oral tentacles with the distal end of the tentacle facing up. Arrowheads point to a subset of POU-IV(-)-expressing epithelial cells, which are abundant in the tentacular ectoderm (ec). Note the cytoplasmic distribution of the POU-IV(-) likely resulting from the lack of nuclear localization signal. (D–F) Sections showing ciliary cone microvilli (mv)-bearing cells. Ciliary cone-bearing epithelial cells express POU-IV(-) (arrowheads). (G–I) Sections at the level of surface ectoderm of developing oral tentacles with the distal end of the tentacle facing up. A subset of POU-IV(-)-expressing cells are Ncol3-positive (arrowheads), representing immature cnidocytes. (J–L) Sections showing an immature cnidocyte which expresses POU-IV(-) and Ncol-3. Note that the cell bears apical microvilli (mv) that do not form a ciliary cone. (M–O) Sections showing immature hair cells in F2 pou-iv -/- N. vectensis polyps injected with pou-iv::kaede construct. Note the presence of ciliary cone microvilli (mv) and basal neurites (ne). (P–R) Sections through tentacles with the distal end facing up. White arrowheads point to nuclei of POU-IV(-)-expressing ectodermal epithelial cells, which are TUNEL-negative. TUNEL-positive, pyknotic nuclei are observed in the endoderm (purple arrowheads). Abbreviations: ec ectoderm; en endoderm; ms muscle fiber. Scale bar: 10 µm.

Figure 6.

Figure 6—figure supplement 1. pou-iv::kaede reporter construct drives transgene expression in hair cells and cnidocytes.

Figure 6—figure supplement 1.

Confocal sections of oral tentacles of Nematostella vectensis polyps injected with pou-iv::kaede construct, labeled with antibodies against Kaede (‘pou-iv::kaede’) and minicollagen 3 (‘Ncol3’). Filamentous actin is labeled with phalloidin (Pha), and nuclei are labeled with DAPI (dapi). Panels A–H show tangential sections at the level of the surface ectoderm. Panels I–L show a side view of a cnidocyte (cn), with the apical cell surface facing up. pou-iv::kaede expression occurs in hair cells (hc in A–D) and cnidocytes (cn in A–L). Arrowheads in A–C indicate stereovilli of hair cells. Cnidocytes have basally localized nuclei (nu) and extend basal neurite-like processes (ne). Scale bar: 10 µm.
Figure 6—figure supplement 2. Cnidocytes in pou-iv null mutants develop basal processes.

Figure 6—figure supplement 2.

Confocal sections of a cnidocyte (cn) in the body column of a F2 pou-iv +/+ polyp injected with pou-iv::kaede construct and labeled with antibodies against Kaede (‘pou-iv::kaede’) and minicollagen 3 (‘Ncol3’). Nuclei are labeled with DAPI (dapi). Panels (A-D) show tangential sections at the level of the basal ectoderm. Note that the cnidocyte extends neurite-like processes (ne). Scale bar: 10 µm.