Pituitary homeobox 1 (Ptx1) is a homeodomain-containing transcription facto
r acting on transcription of all pituitary hormone genes. Its expression is
first detected in the stomodeal ectoderm and is maintained in all derivati
ves of this structure, including Rathke's pouch. We now show that Ptx1 is e
xpressed in all pituitary cells but that it is differentially expressed in
different lineages at both the messenger RNA and protein levels. On day 12.
5 of mouse embryonic development, cells expressing the highest levels of Pt
x1 are restricted to the forming pars tuberalis, also called the rostral ti
p, a region where the first alpha-glycoprotein subunit-expressing cells app
ear. Coimmunolocalization studies reveal that alpha-glycoprotein subunit-po
sitive cells express the highest levels of Ptx1 throughout; development and
in the adult gland. The quantitative differences in Ptx1 expression in pit
uitary cell lineages may relate to a role in cell proliferation, lineage co
mmitment, and/or the control of organ development.