Ptx1, a bicoid-related homeo box transcription factor involved in transcription of the pro-opiomelanocortin gene.

Abstract

The pituitary gland contains six distinct hormone-producing cell types that arise sequentially during organogenesis. The first cells to differentiate are those that express the pro-opiomelanocortin (POMC) gene in the anterior pituitary lobe. The other lineages, which appear later, include cells that are dependent on the POU factor Pit-1 and another POMC-expressing lineage in the intermediate pituitary lobe. Using AtT-20 cells as a model for early expression of POMC in the anterior pituitary, we have defined a regulatory element conferring cell specificity of transcription and cloned a cognate transcription factor. This factor, Ptx1 (pituitary homeo box 1), contains a homeo box related to those of the anterior-specific genes bicoid and orthodenticle in Drosophila, and Otx-1 and Otx-2 in mammals. Ptx1 activates transcription upon binding a sequence related to the Drosophila bicoid target sites. Ptx1 is the only nuclear factor of this DNA-binding specificity that is detected in AtT-20 cells, and it is expressed at high levels in a subset of adult anterior pituitary cells that express POMC. However, Ptx1 is expressed in most cells of Rathke's pouch at an early time during pituitary development and before final differentiation of hormone-producing cells. Thus, Ptx1 may have a role in differentiation of pituitary cells, and its early expression pattern suggests that it may have a role in pituitary formation. In the adult pituitary gland, Ptx1 appears to be recruited for cell-specific transcription of the POMC gene.

How to make a teleost adenohypophysis: Molecular pathways of pituitary development in zebrafish

“…This suggests that in fish pitx3 has possibly subsumed the function of mammalian Pitx1/2. By trans-activating reporter assays it was shown that mouse Pitx1 can drive Lhx3 (the mouse homolog of zebrafish lim3) as well as prl and pomc expression (Lamonerie et al, 1996, Tremblay et al, 1998. Since Pitx binding sites have also been found in the zebrafish pomc promoter, and since lactotropes and corticotropes are the first differentiating AH cells of the zebrafish, one can speculate about a similar regulation of these genes by Pitx3 in teleosts (Liu et al, 2003).…”

Rice bicoid-related cDNA sequence and its expression during early embryogenesis

“…To approach the similar mechanism of maternal regulation in embryo development, some bicoidrelated genes are recently reported in chick [15], [17] mouse [18] and other animals, which are mostly characterized by the lys-9 of helix3 [16]. However, there is still not any bicoid-related gene reported in higher plant yet, although the polarity of embryo has been reported in higher plant (2).…”

“…To compare the homeodomain conserved region between RB24, Drosophila bicoid gene [14], [1] and other chicken and mouse bicoid-related genes [15], Block Maker software were used for analysis of highly conserved regions of proteins. The results indicates two conserved block regions in bicoid (Drosophila), and Rb24(rice), Ptx1(chicken), Gsc(mouse), Otx1(mouse) bicoid-related genes, which just cover putative helix1 and helix3 region in bicoid homeodomain (Fig 1A).…”

Expression of Pituitary Homeo Box 1 (Ptx1) in Human Non-Neoplastic Pituitaries and Pituitary Adenomas

“…Ptx1 is closely related to the mammalian Otx gene, which is expressed in the rostral brain during the process of development (37,38), and Otx2 is a fundamental factor related to forebrain and midbrain development in mice (39). Ptx1 mRNA is strongly expressed in adult corticotroph cells, which secrete POMC, whereas its expression in Rathke's pouch has also been detected using the in situ hybridization technique (17). Thus, there remains a possibility that Ptx1 is expressed in pituitary cells other than corticotrophs, so that its activities need further investigation, including the relationship with other transcription factors related to pituitary cells.…”

“…Therefore, the activation of Pit-1 by Prop-1 may be triggered through the disappearance of Rpx/Hesx-1. On the other hand, a novel transcription factor pituitary homeo box 1 (Ptx1) has been initially introduced as a factor toward the expression of proopiomelanocortin (POMC) (17). But, in the studies on rat pituitary glands and cultured cells, Ptx1 has been expressed not only in the POMC secreting cells but also in the other hormone secreting cells of the anterior lobe as well as in the cell lines of various different hormone productions (16).…”