The Zebrafish Pronephric Nephrons Consist of Multiple Tubule Segments Similar to Metanephric Nephrons. (A) Whole-mount in situ hybridization of wild-type embryos shows segmentation of each pronephric nephron into podocytes (Pod), neck (N), proximal convoluted tubule (PCT), proximal straight tubule (PST), distal early (DE), corpuscle of Stannius (CS), distal late (DL), and pronephric duct (PD) that fuse to the cloaca (C) (not shown). Lateral views are shown except for dorsal view in top left panel, with anterior to the left. (B) Murine section in situ hybridzation of solute transporters, bar denotes 500 μm. (C) Time course of PCT convolution and adjacent PST, with slc20a1a expression used to label the PCT at all stages, PST labeled by trpm7 expression at 26 hpf, and slc13a1 expression at 48–144 hpf. (D) Expression of cdh17, slc9a3, and rfx2 at 48 hpf in distinct segments of the pronephros. Note expression of rfx2 in the presumptive ciliated neck segment. (C and D) Dorsal views are shown, with anterior to the left. (E) Schema of the original model of the 48 hpf zebrafish pronephros (top), our redefined model showing segmentation of each nephrons (middle), and a mammalian nephron stretched out to compare segmentation of the metanephric nephron (bottom). Mammalian segments are color coded according to observations of shared solute transporter expressions with respective zebrafish pronephros segments. Additional abbreviations are: G (glomerulus), N (neck), TL (thin limb), TAL (thick ascending limb), MD (macula densa), DCT (distal convoluted tubule), CNT (connecting tubule), and CD (collecting duct).
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