Figure 5

Histologic cross sections of 7-chaetiger juveniles showing further details of Nar - lim1 expression. All sections are orthogonal to the AP axis; dorsal is to the top. Dashed lines separate sections spaced apart by 5 μm in (C), (E), (Q) and 10 μm in (I) (the more posterior section is to the right or below the line). (D), (G), (I) Acetylated α-tubulin immunolabeling. (A) Same AP position as Figures 3A, B. (B) Anterior-most level of the brain’s neuropil. (C) Upper quadrant of the head; the mid-sagittal plane is flush with each image’s right edge. (D) Same AP position as (C). (E) Posterior brain and anterior pharynx. (F-J) Three positions within the pharynx: anterior jaws (F), (G), posterior jaws (H), (I), and caudal-most (J). Arrowheads point to exposed portions of commissural nerves; double arrowheads point to longitudinal nerves; arrows point to exposed portions of medial nerves connecting ipsilateral ganglia. (K-N) Various positions within the 5th and 6th ganglion pairs of the ventral nerve cords. (O-T) Nar-lim1 expression during parapodial development. Brackets indicate mesodermal expression; arrows mark expression in parapodial ganglia. (O) Nascent segment nearest the pygidium. (P) Nascent segment approximately 20 μm anterior to (O). (Q) Youngest outgrowing parapodium; approximately 50 μm anterior to (P). Inset images show additional sections through the chaetal sac, 10 and 15 μm anterior to main image, respectively. (R) Youngest chaetigerous (sixth) parapodium. (S), (T) First pair of parapodia (left and right, respectively) from the same section; one shows the nel (S), and the other the vnl (T). ac anterior cirri, ae anterior eye, br brain, chs neuropodial chaetal sac, cpr ciliary photoreceptor cells, dc dorsal cirrus, ja jaw, necl neuropodial chaetal lobe, nel neuropodial ligule, np neuropil, pa palp, pe posterior eye, ph pharynx, vc ventral cirrus, vnc ventral nerve cords, vnl ventral notopodial ligule.