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The last step of oestrogen biosynthesis is catalyzed by the enzyme aromatase, the product of the cyp19a1 gene. In vertebrates, cyp19a1 is expressed in the brain resulting in a local oestrogen production that seems important not only for the control of reproduction-related circuits and sexual behaviour, but also for the regulation of neural development, synaptic plasticity and cell survival. In adult amphibians, the precise sites of expression of cyp19a1 in the brain have not been investigated which prevents proper understanding of its potential physiological functions. The present study aimed at examining the precise neuroanatomical distribution of cyp19a1 transcripts in adult brains of both male and female Xenopus. We found that cyp19a1 expression is highly regionalized in the brains of both sexes. The highest expression was found in the anterior part of the preoptic area and in the caudal hypothalamus, but significant levels of cyp19a1 transcripts were also found in the supraoptic paraventricular and suprachiasmatic areas, and in brain regions corresponding to the septum, bed nucleus of the stria terminalis and amygdala. Importantly, no obvious difference between male and female Xenopus was detected at the level of cyp19a1 transcripts. Additionally, in the brain of adult Xenopus, cyp19a1 transcripts were detected in neurons, and not in glial cells. These data and those available in other vertebrates on cyp19a1/aromatase expression suggest that, with the intriguing exception of teleost fishes, cyp19a1 was under strong evolutionary conservation with respect to its sites of expression and the nature of the cells in which it is expressed.
Fig. 1. Distribution of cyp19a1 transcripts in adult Xenopus brain in both male (A1–K1) and female (A3–K3). Images of transverse sections through the whole rostrocaudal axis of male and female brains (Images are arranged in a rostral to caudal order). A2–K2 are the DAPI stained images, that exactly or approximately match the male (A1–K1) and the female (A3–K3) brain section images, respectively. Arrows and arrowheads highlight some areas of labelling. For all images, dorsal is to the top. Scale bar = 400 μM. (L) Quantification of cyp19a1 transcripts in the six adult specimens. Graph show the count of the cyp19a1-labelled pixels at different rostro-caudal brain levels (from level A–K as illustrated in Fig. 1, Fig. 2). The error bars represent s.e.m. BNST (bed nucleus of the stria terminalis), Sept (septum), aPOA (anterior preoptic area), POA (preptic area), SCN (suprachiasmatic nucleus), Hyp (hypothalamus).
Fig. 2. Distribution of cyp19a1 transcripts in adult Xenopus brain in both male (A1–K1) and female (A3–K3). Images of transverse sections through the whole rostrocaudal axis of male and female brains (Images are arranged in a rostral to caudal order). A2–K2 are the DAPI stained images, that exactly or approximately match the male (A1–K1) and the female (A3–K3) brain section images, respectively. Arrows and arrowheads highlight some areas of labelling. For all images, dorsal is to the top. Scale bar = 400 μM. (L) Quantification of cyp19a1 transcripts in the six adult specimens. Graph show the count of the cyp19a1-labelled pixels at different rostro-caudal brain levels (from level A to K as illustrated in Fig. 1, Fig. 2). The error bars represent s.e.m. BNST (bed nucleus of the stria terminalis), Sept (septum), aPOA (anterior preoptic area), POA (preptic area), SCN (suprachiasmatic nucleus), Hyp (hypothalamus).
Fig. 3. High magnifications of cyp19a1 transcripts distribution in the preoptic area and caudal aspect of hypothalamus in both male (A, C and E) and female (B, D) brains. Male hypothalamus adjacent sections labelled for cyp19a1/Dapi (E), Vimentin/Dapi (F) or Neuroβtubulin alone (G). Dorsal is to the top. For the caudal hypothalamus (C, D), only the half left side is shown. Scale bar = 50 μM.
Fig. 4. Expression pattern of cyp19a1 gene (A1–E1) compared to Neuro-β-tubuline (A2–E2) and Vimentin (A3–E3) gene expression patterns in representative transverse sections of adult Xenopus brain. At each brain section level, image series 2 and 3 are adjacent sections of the transverse section shown in image series 1. Dorsal is to the top. Scale bar = 400 μM.
