Fig. 2

Molecular patterning of the tail epidermis regulates median fin formation. A–C Schematic representation of an early tailbud (A), a larva in lateral view (B), and a cross-section of the larval tail (C) with the embryo/larva itself in gray surrounded by the tunic. The tail epidermal neurogenic midlines that lie where median fins are positioned are highlighted in light blue. D–F Effects of BMP pathway modulation on median fin formation: control (BSA- and DMSO-treated larva) (Dii), DMH1-treated larva did not develop a ventral fin (Eii), and BMP2-treated larva with an excess of tunic making bulges (Fii). G–I Effects of CRISPR/Cas9 gene inactivation on tunic formation: Tyr-CRISPR larva formed a normal tunic with fins but lacked pigment cells (Gii), Msx-CRISPR larva lacked both ventral and dorsal median fins and had normal pigment cells (Hii), and Klf1/2/4/17-CRISPR larva presented indentations in the median fin that had an undulated shape (Iii). CBM3a-GFP staining of larvae in D–I (green). Insets in Gii and Hii: transmitted light picture of the trunk. Inset in Iii: dorsal view focused on the median fin. Larvae are shown in lateral view with anterior to the left and dorsal to the top. On the left panels (i): schematic representation of the distribution of the midline fate (light blue) in the different conditions. White arrows highlight the absence of median fin. Individual data values can be found in Additional file 7: Table S1. Scale bar: 100 µm