Expression of Ptx1 in the adult rat pituitary glands and pituitary cell lines: hormone-secreting cells and folliculo-stellate cells

Abstract

The pituitary homeobox1 gene (Ptx1) was initially identified as encoding a pituitary-restricted transcription factor for the proopiomelanocortin (POMC) gene. In order to elucidate the expression pattern of the Ptx1 protein, we investigated the localization of the protein in adult rat pituitary gland and in various pituitary cell lines. We produced an antibody specific for Ptxl protein, and confirmed its specificity by Western blot analysis. Immunohistochemically, many nuclei in the anterior pituitary cells as well as in the intermediate cells were positive for Ptxl staining with this specific antibody. Immunohistochemical double staining revealed the presence of Ptx1 not only in all types of hormone-secreting cells but also in some folliculo-stellate (FS) cells. Furthermore, the expression of Ptx1 mRNA was confirmed in various pituitary cell lines and in the FS cell line by using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Our studies indicated that Ptxl may not only play a role as a basic transcriptional factor for production of various hormones, but may also play some important role(s) in FS cells. Possible synergistic actions with other factors remain to be investigated. The novel finding of Ptx1 in FS cells is of particular interest, and may suggest that FS cells and hormone-secreting cells are derived from a common cellular ancestor.

Fig. 1

Western blot analysis to confirm the specificity of the anti- Ptx1 antibody (lane 1). The Ptx1 protein was detected as single band at 35 kDa (lane 2). The Ptx1 signal was decreased by use of preadsorbed antibody

Fig. 2a-i

Immunohistochemical co-localization of Ptx1 (brown) and pituitary hormones or S-100 protein (blue) in rat pituitary. Ptxl was detected in the nuclei of intermediate lobe (IL) and anterior lobe (AL) (a), and it was expressed in the nuclei of cells containing POMC (b), ACTH (c), GH (d), PRL (e), TSHβ (f), α-SU (g), FSHβ (h), and S-100 protein (i). ×600(a-i)

Fig. 3

RT-PCR analysis of expression of Ptx1 mRNA and β-actin mRNA.Ptx1 mRNA was detected in male and female rat pituitary glands and all hormone-secreting cell lines examined. The Ptx1 PCR products were detected at 298 bp. The negative control without RT showed no formation of the PCR product from the rat pituitary RNA. The β-actin primers were used as internal standards, and yielded PCR products in all samples. The β-actin PCR products were detected at 105 bp

Fig. 4a, b

Immunocytochemical detection of Ptx1 in pituitary cell lines. Ptx1 was detected in the nuclei of the αT3–1 cell line (a) and TtT/GF cell line (b). x650 (a,b)