Eagleson GW et al. (1986), The pituitary adrenocorticotropes originate fro...

XB-ART-28649

J Embryol Exp Morphol 1986 Jun 01;95:1-14.

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The pituitary adrenocorticotropes originate from neural ridge tissue in Xenopus laevis.

Eagleson GW , Jenks BG , Van Overbeeke AP .

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A series of grafting experiments was conducted to determine pituitary origins prior to brain tube closure in Xenopus laevis. Extirpation experiments indicated that the ventral neural ridge (VNR) tissue of stage-18+ embryos was essential for pituitary development. Bolton-Hunter reagent was used to label stage-18+ VNR tissue with 125I, and this tissue was then returned to the donor and its subsequent ontogenesis followed. Labelled tissue was ultimately found in the ventral hypothalamus, the ventral retina, and the anterior pituitary. Using immunocytochemical techniques with antisera to adrenocorticotropin (ACTH), it was found that some of the VNR-derived cells were corticotropes. A region of the nucleus infundibularis which was radioactive labelled also gave ACTH-positive immunoreaction. This might indicate that some ACTH-containing neurones of the hypothalamus are VNR in origin. We suggest that stage-18+ VNR is the site of attachment of brain and anterior pituitary ectoderm. Part of this adherence point is eventually incorporated into the anterior pituitary and will form corticotropes. It is concluded that the ventral retina, the preoptic region of the hypothalamus, some hypothalamic ACTH-immunoreactive cells, and the most anterior portion of the adenohypophysis are all ventral neural ridge in origin.

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Species referenced: Xenopus laevis
Genes referenced: pomc por
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	Fig. 1. (A,B) Appearance of donor and host embryos shortly after removing ventral ridge tissue from donor embryo and grafting it in host fin. (A) Epidermal tissue quickly grows over the excised region of donor (arrow). (B) The tissue graft survives in host fin (arrow). (C,D) Appearance of stage-42 larvae of donor and host embryo. The melanin pigment of dermal melanophores of donor larvae remains in a punctuate condition indicating a lack of pituitary melanotropin (C) while the host larvae display hyperpigmentation (D). Arrow indicates position of graft in host larvae.
	Fig. 2. (A) Xenopus larvae which had their stage-18+ VNR extirpated, completely lacked a hypophysis (single arrow). The infundibulum was unaffected by this operation. The preoptic recess usually exhibited minor breaks and tears (small arrows), oc, optic chiasma. Bar, 0-1 mm. (B) The grafted stage-18+ VNR was allowed to develop in hosts. This grafted tissue rolled up and formed a spinal-cord-like structure. It often induced vacuolation within host spinal tissue, g, graft; m, melanophores; nc, host neural cord;/, fin epidermis of host. Bar, 0-1 mm.
	Fig. 3. Schematic diagram of procedure to radiolabel ventral neural ridge tissue with 125I.
	Fig. 4. Autoradiographic analysis of stage-42 embryo, the VNR of which was radiolabelled at stage 18+. Radiolabelled stage-18+ VNR tissue consistently contributed to the formation of three distinct organs. The edges of the VNR eventually became localized within ventral retinal tissue. The ventral portion of the VNR was localized within the anterior pituitary. The bulk of the VNR tissue was found within the anterior hypothalamus just anterior to the preoptic recess (por), pa, preoptic area;pg, pituitary gland; r, retina. Bars, 0-1 mm.
	Fig. 5. Morphogenetic movements of the labelled stage-18+ VNR. (A) At stage 30 most of the label is observed within the anterior forebrain in the region of the chiasmatic ridge (cr). The outline of the pituitary primordium (pp) is indicated with a dotted line. No label was found within the primordium. (B) At stage 33/34 the pituitary primordium has detached or is torn free from the preoptic area (pa). Thus the most anterior portion of this pituitary anläge is labelled (arrow). Also indicated is the preoptic recess (por) and the optic chiasma (oc). (C) By stage 42, the pituitary gland (pg) is under the infundibulum and label becomes incorporated within the adenohypophysis (arrow). Bars, 0-1 mm.
	Fig. 6. The radiolabelled VNR (A) shows a strong correlation with the ACTH immunoreactive cells (B). Even the hypothalamic area (nucleus infundibularis ventralis) that exhibits label corresponded to an ACTH-immunoreactive area (indicated by arrow), por, preoptic recess; oc, optic chiasma; pd, pars distalis; me, median eminence; pi, pars intermedia. Bar, 0-1 mm.
	Fig. 7. Schematic illustration of the most probable morphogenetic events leading to the labelling of three distinct brain regions. Stage 18: introduction of the radiolabelled VNR tissue. Stage 19: internalization of the radiolabelled tissue during epidermal overgrowth and brain tube fusion. Stage 22: attachment of overlying epidermis occurs along suture line of involuted VNR tissue. Stage 32: proliferation of prosencephalon within the radioactive VNR tissue subdivides the label into two areas. Stage 42: further proliferation results in the final distribution of radiolabelled areas.