Expression of glial progenitor markers p75NTR and S100 protein in the developing mouse parathyroid gland.

Drosophila glial cells missing (Drosophila Gcm) is a transcription factor that is required for the differentiation of glial cells. Gcm2, a mouse homologue of Drosophila Gcm, is a master regulatory gene of parathyroid development and is expressed in the parathyroid rudiment. We have found that the mouse parathyroid exhibits the glial progenitor markers, p75(NTR) and S100 protein, during fetal development. At embryonic day 11.5 (E11.5), a bulge of the parathyroid rudiment is formed in the cranial part of the third pharyngeal pouch. The rudiment exhibits immunoreactivity for p75(NTR) and S100 protein, in addition to secretory protein 1/chromogranin A. While the thymus rudiment, which arises from the caudal part of the third pharyngeal pouch, is moving downwards, the parathyroid is attached to the top of thymus. The parathyroid comes into contact with the thyroid lobe at E13.5 and then separates from the thymus. The parathyroid maintains intense immunoreactivity for p75(NTR) and S100 protein during the migration and development in the thyroid lobe. The co-localization of p75(NTR) and S100 in the developing parathyroid cells has been confirmed by confocal microscopy. Other glial markers, viz. glial fibrillary acidic protein, Sox10, vimentin and nestin, are not expressed in the parathyroid at any stage of development. The neural progenitor markers, neurofilament 160 and TuJ1, are also absent from the parathyroid. Taken together, we suggest that Gcm2 supplies only some glial progenitor characteristics to the parathyroid rudiment.