Fig. 4. Defective migration of GnRH-neurons from the olfactory epithelium to the hypothalamus. (A,C,E) Normal controls; (B,D,F,G) Ebf2^-/- coisogenic mutants; (A,B) E15; (C,D,G) P0; (E,F) P30. (A) In E15 wild-type embryos, migrating GnRH-neurons (arrows, brown staining, nuclear counterstaining in cyan) are mostly located dorsal to the cribriform plate (cp) and ventral to the olfactory bulb (ob). (B) Mutant neurons (arrows) migrate slowly out of the vomeronasal organ (vno). (Inset) Mutant neurons form dense clusters, often devoid of leading or trailing processes. (C) GnRH-positive fibers (arrows) reach the median eminence (ME) of the hypothalamus in wild-type newborn brains. (D) No GnRH immunostaining in the ME of mutant P0 brains. (E) GnRH-positive neurons (brown) in the preoptic region of the wild-type hypothalamus. (F) No GnRH immunostaining in the corresponding region of mutant brains. (G) At birth, mutant GnRH-positive neuronal cell bodies (black arrowheads) and fibers (white arrowheads) are ectopically located in the forebrain close to the midline at the interface between olfactory bulb (ob) and rostral telencephalic cortex (cx), dorsal to the nasal septum (ns) and cribriform plate. See empty box in inset for localization. Arrow in inset indicates physiological migration route. cp, cribriform plate; cx, telencephalic cortex; ME, median eminence; ns, nasal septum; ob, olfactory bulb; vno, vomeronasal organ. Scale bars: 100 µm in A-F; 50 µm in G.

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