Fig. 4

Neurogenesis is restricted to the central and peripheral edge of the sensory neuroepithelium. (A) In situ-hybridization for the early neurogenesis markers achaete scute-like 1a (ascl1a) and delta-like a (dla), and the late differentiation markers neuronal differentiation 4 (neurod4) and growth associated protein 43 (gap43) on full cross sections through the adult OE (top) and higher power views of one side of the OE (bottom). Expression of the neurogenic markers is restricted to the interlamellar curves (asterisks) and sensory/nonsensory border (dotted line). The solid line indicates the outline of the section. Scale bars: 100 µm (top panel), 50 µm (bottom panel). (B) Ascl1a-expressing cells are actively dividing. In situ hybridization for ascl1a (red) and immunohistochemistry against BrdU following 24 h incubation with the marker to highlight dividing cells. Double positive cells (arrowheads) can be identified at the interlamellar curves (asterisks) and the sensory/nonsensory border (dotted line). Scale bar: 50 µm. (C) Quantification of the distribution of cells expressing the neurogenic markers ascl1a, dla, and neurod4 at the interlamellar curves (ILC) and sensory nonsensory border (SNS; means ± SEM for ascl1: 8 sections from 2 fish, dla: 9 sections from 3 fish, neurod4: 8 sections from 2 fish). Cells expressing the markers are unevenly distributed between the two proliferation zones; more ascl1a- and dla-expressing cells can be found at the SNS, whereas more neurod4-positive cells locate to the ILC. (D) Immunohistochemistry against the mitotic marker proliferating cell nuclear antigen (PCNA, green) and the neuronal stem cell marker sox2 (red) on a single whole mount olfactory lamella. Two rows of dividing cells can be identified in the peripheral nonsensory OE, cells at the inner band (arrows) are double positive for sox2 and appear yellow, while dividing cells in the peripheral OE (arrowheads) are devoid of sox2 expression. Note that most of the double-positive dividing cells at the interlamellar curve (left end of the lamella) are not included due to the dissection of the lamella.