Fjx1, the murine homologue of the Drosophila four-jointed gene, codes for a putative secreted protein expressed in restricted domains of the developing and adult brain

The Drosophila gene four jointed (fj) codes for a secreted or cell surface protein important for growth and differentiation of legs and wings and for proper development of the eyes. Here we report the cloning of the mouse fou r-pointed gene (fjx1) and its pattern of expression in the brain during emb ryogenesis and in the adult. In the neural plate, fjx1 is expressed in the presumptive forebrain and midbrain, and in rhombomere 4, however a small ro stral/medial area of the forebrain; primordium is devoid of expression. Exp ression of fjx1 in the neural tube can be divided into three phases. (1) In the embryonic brain fjx1 is expressed in two patches of neuroepithelium: i n the midbrain tectum and the telencephalic vesicles. (2) In fetal and earl y postnatal brain fjx1 is expressed mainly by the primordia of layered tele ncephalic structures: cortex (ventricular layer and cortical plate), olfact ory bulb (subependymal layer and in the mitral cell layer). In addition exp ression is observed in the superior colliculus. (3) In the adult, fjx1 is e xpressed by neurons evenly distributed in the telencephalon (isocortex, str iatum, hippocampus, olfactory bulb, piriform cortex), in the Purkinje cell layer of the cerebellum, and numerous medullary nuclei. In the embryo, stro ng expression can further be seen in the apical ectodermal ridge of fore- a nd hindlimbs and in the ectoderm of the branchial arches. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.