RET receptor in the gut of developing cat.

RET receptor is a transmembrane protein which, together with the glial-cell-line derived neurotrophic factor family receptors alpha, forms a receptor complex upon activation by the glial-cell-line-derived neurotrophic ligands (GFLs). RET signaling is crucial for: (a) development of the enteric nervous system and kidney; (b) development of sympathetic, parasympathetic, motor, and sensory neurons; (c) postnatal maintenance of dopaminergic neurons; (d) spermatogenesis. In humans, RET mutations cause the Hirschsprung???s disease, characterized by megacolon aganglionosis, and different types of cancer, the multiple endocrine neoplasia type 2A and type 2B and familial medullary thyroid. In the earliest aged cat embryos studied (stage 9 according to Knopse), RET immunoreactivity (IR) was observed in few cells detected in bilateral rows extending latero-ventrally to the neural tube and dorsolaterally to the foregut. In the successive aged group (stage 11), RET IR was observed in few single or grouped epithelial cells of the anterior gut and in small clustered cells scattered in the mesenchyme around the anterior gut. From stage 14???22 (the last stage 22 includes foetuses around the birth), RET IR was seen in neurons and fibers of the enteric nervous system. The appearance and intensification of RET-IR in the gut occurred with cranio/caudal and external/internal directions during the development. These results, thus, suggest the involvement of GFLs in the neuroblast migration, proliferation and differentiation. For a short period of development, these molecules might also act on some cells of the epithelium