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???displayArticle.abstract??? Cytochrome P450aromatase (P450arom; aromatase) is a microsomal enzyme involved in the production of endogeneous sex steroids by converting testosterone (T) into oestradiol (E2). Aromatase is the product of the cyp19a1 gene and plays a crucial role in the sexual differentiation of the brain and in the regulation of reproductive functions. In the brain of mammals and birds, expression of cyp19a1 has been evidenced essentially in neuronal populations of the telencephalon and diencephalon. In contrast, a wealth of evidence established that in teleost fishes, aromatase expression in the brain is restricted to radial glial cells. The current study investigated the precise neuroanatomical distribution of cyp19a1 mRNA during brain development in Xenopus laevis (late embryonic to juvenile stages). For this purpose, we used in situ hybridization alone or combined with the detection of a proliferative (PCNA), glial (BLBP, Vimentin) or neuronal (Acetyl-tub; HuC/D; NeuroβTubulin) markers. We provide evidence that cyp19a1 expression in the brain is initiated from very early larval stage and remains strongly detected until juvenile and adult stages. At all stages analysed, we found the highest expression of cyp19a1 in the preoptic area and the hypothalamus as compared to the rest of the brain. In these two brain regions, cyp19a1-positive cells were never detected in the ventricular layers. Indeed, no co-labelling could be observed with radial glial (BLBP, Vimentin) or dividing progenitors (PCNA) markers. On the contrary, cyp19a1-positive cells perfectly matched with the distribution of post-mitotic neurones as shown by the use of specific markers (HuC/D, Acetyl-tub and Neuroβtubulin). These data suggest that, similar to what was found in other tetrapods, aromatase in the brain of amphibians is found in post-mitotic neurones and not in radial glia as reported in teleosts. This article is protected by copyright. All rights reserved.
Figure 1. Expression pattern of cyp19a1 (CYP) (a1–f1 and a2–f2) compared to Vimentin (VIM) (a3–f3) in the Xenopus laevis prometamorphic larva (NF stage 58) brain. Top: dorsal view of the X. laevis brain. Letters correspond to the rostrocaudal location of transverse sections as depicted in the whole brain drawing. Illustrations (a2) to (f2) correspond to higher magnifications of (a1) to (f1) and to adjacent sections of (a3) to (f3). Arrows and arrowheads highlight less conspicuous areas of labelling. For all images, dorsal is to the top. Scale bars = 100 μm.
Figure 2. Expression pattern of cyp19a1 (CYP) (g1–k1 and g2–k2) compared to Vimentin (VIM) (g3–k3) in the Xenopus laevis prometamorphic larva (NF stage 58) brain. Letters correspond to the rostrocaudal location of transverse sections as depicted in the whole brain drawing of Fig.1. Illustrations (g2) to (k2) correspond to higher magnifications of (g1) to (k1) and to adjacent sections of (g3) to (k3). (l–n) Control in situ hybridisation experiments using cyp19a1 sense (m) or antisense (l and n) probes on X. laevis (l and m) or Xenopus tropicalis transverse sections. For all images, dorsal is to the top. Scale bars = 100 μm.
Figure 3. Distribution of cyp19a1 (CYP) transcripts at different brain developmental stages. In situ hybridisations for cyp19a1 at late embryonic stage 42 (NF42; a, b); at premetamorphic stages NF47 (c, d), NF49 (e, f) and NF52 (g, h); and at prometamorphic NF58 (i, j), metamorphic NF62 (k, l) and post-metamorphic NF66 (juvenile; m, n) stages. For all developmental stages, transverse sections at the levels of the preoptic area (POA) (a, c, e, g, i, k, m) and hypothalamus (b, d, f, h, j, l, n) are shown. Arrows highlight less conspicuous areas of labelling. (l–n) For all images, dorsal is to the top. Scale bars = 100 μm.
Figure 4. Cyp19a1/brain lipid binding protein (BLBP) and Cyp19a1 (CYP)/proliferating cell nuclear antigen (PCNA) double-stainings in the preoptic and hypothalamic areas of metamorphic (NF62) brain. Transverse sections at the level of the preoptic area (a–i) or hypothalamus (j–r). Arrows in (a) and (j) indicate the precise location of the high magnifications illustrations (b–i) and (k–r), respectively. In situ hybridisation using a cyp19a1 probe (CYP) combined with BLBP (b, e, f, k, n, o) or PCNA (c, h, i, l, q, r) immunohistochemistry. To allow a merge with the 4’,6-diamidino-2-phenylindole (DAPI) staining, colours of BLBP and PCNA immunostainings in (b), (c), (k) and (l) are changed. Asterisks in (k), (n) and (o) indicate background labelling. For all images, dorsal is to the top. Scale bar = 100 μm in (a) and (j); 50 μm in (b–i) and (k–r).
Figure 5. Cyp19a1 transcripts distribution compared to several neuronal markers on juvenile (a–c) and adult (d–f) preoptic area transverse sections. (a–c) Cyp19a1 (CYP) in situ hybridisations (a, c) combined with acetylated tubulin (TUB) immunodetections (b, c). Arrows indicate some double-stained cells. (d–f) Comparison between Cyp19a1 (CYP) in situ hybridisation (d), HuC/D immunodetection (HU) and Neuroβtubulin (NβT) in situ hybridisation on adjacent sections. For all images, dorsal is to the top. Scale bar = 50 μm.
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