||Figure 2. Comparative aspects of the preoptic-hypothalamic (POH) boundary between amphibians and reptiles. Photomicrographs of transverse sections through the developing preoptic-hypothalamic territory of Xenopus
(A–C) and Pseudemys
(E–G) illustrating its molecular profile based on the combinatorial expression of different transcription factors and neuropeptides indicated in each photomicrograph. The developmental stage in the cases of Xenopus is also marked. (D) and (H) are summarizing schemes of lateral views of the brains in which the main molecular features of the POH are illustrated according to the color code indicated. In both schemes, a transverse section through the level indicated on the lateral view of the brain is illustrated. Note that the coordinate system for the hypothalamus rotates 90° because the longitudinal axis of the brain bends in the diencephalon, and this is also the case for all photomicrographs of sagittal sections in all figures. For abbreviations, see list. Scale bars = 50 μm (A,B), 100 μm (C,F,G), 200 μm (E).