McCoy KE et al. (2008), Collectrin/tmem27 is expressed at high levels i...

XB-ART-37154

Gene Expr Patterns 2008 Apr 01;84:271-4. doi: 10.1016/j.gep.2007.12.002.

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Collectrin/tmem27 is expressed at high levels in all segments of the developing Xenopus pronephric nephron and in the Wolffian duct.

McCoy KE , Zhou X , Vize PD .

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Collectrin/tmem27 encodes a transmembrane protein that plays a critical role in amino-acid transport. Originally described as being expressed only in collecting ducts, it has subsequently also been shown to also be expressed in the S1 segment of the proximal tubule of mammalian metanephric nephrons. In this report we describe the expression of collectrin in the simple embryonic kidney of amphibians, the pronephros. Each pronephros contains a single large nephron with a proximo-distal segmentation very similar to that of mammalian metanephric nephrons. Analysis of collectrin expression in pronephroi at a variety of embryonic stages indicates that this gene is expressed at very high levels throughout the pronephric system, including proximal and distal segments and the Wolffian duct. Expression in the pronephros commences at Xenopus embryonic stage 28 which corresponds to when epithelialization begins within the pronephric mesenchyme. Like the Na+K+ATPase/atp1a1, another highly expressed pronephric marker, collectrin is also expressed in the cloaca but not in the cloacal derived posterior segment of the Wolffian duct, the rectal diverticulum. Unlike the Na+K+ATPase, which is expressed at lower levels in proximal portions of the pronephric nephron, expression of collectrin is even throughout all of the pronephric epithelia. This expression domain extends far beyond that shown to express amino-acid transporters and indicates collectrin may function in facilitating additional transport processes. Its high level of expression and broad distribution make it an excellent marker with which to examine pronephric kidney development.

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Species referenced: Xenopus
Genes referenced: atp1a1 cltrn slc12a1

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	Fig. 2. Colorimetric in situ localization of collectrin transcription. The embryonic stage (Nieuwkoop and Faber, 1994) of each sample is displayed in the top right corner. Magnified views of each of the embryos illustrated in the left column are shown on the right. Collectrin expression is limited to the developing pronephros, otic vesicle and cloaca. Expression is notably absent from the portion of the nephric duct derived from the rectal diverticulum. In addition, expression increases in the pronephric epithelia at later stages, while cloacal and otic vesicle expression decreases. The faint diffuse staining in the head region is background and does not represent collectrin expression.
	Fig. 3. Histological examination of collectrin expression in pronephric duct epithelia. A transverse section of a stage 35 embryos, stained for collectrin expression as shown in Fig. 2. Following sectioning the sample was counter stained with eosin. The inset shows an enlargement of the pronephric duct region.
	Original version (not included in published version) of figure 2 with additional stage (top right of each image). tmem27 expression in Xenopus laevis
	Fig. 4. Two color fluorescent in situ of collectrin contrasted to other pronephric marker genes. The developmental stage of each sample is indicated in the top right corner of each panel (Nieuwkoop and Faber, 1994). The first column to the left (A, E, I, M) shows collectrin expression in red, the second column (panels B, F, J, N) nkcc2/slc12a1, a segmental marker, in green. The third column from the left (C, G, K, O) illustrates an overlay of these expression patterns, with regions of overlap appearing yellow. The last column (D, H, L, P) shows Na+K+ATPase expression in green. The bottom row (M–P) is a magnified view of (I–L), displaying the pronephros. pt, proximal tubules. Collectrin is first detected with fluorescent in situ at approximately stage 28, and increases in subsequent stages. Collectrin, as compared with Na+K+ATPase, is more uniformly distributed throughout the pronephros (compare M and P), suggesting its use as a general pronephric marker. Furthermore, note the strong expression of collectrin in the proximal tubules (O), unlike the weaker expression of Na+K+ATPase in this region (P).