The anterior pituitary-specific transcription factor POU1F1 was initially identified and cloned as a transactivator of prolactin (PRL), growth hormone (GH), and TSHβ-subunit genes (Bodner et al., 1988; Ingraham et al., 1988). Transcription produces 2 alternatively spliced mRNAs α (NM_000306.2) and β (NM_001122757.1).

The human POU1F1 gene is composed of 6 exons (Theill et al., 1992).

Two transcripts have been reported for this gene.

The main protein isoform expressed in pituitary cells is POU1F1α. This isoform, also named PIT-1.b or PIT-1α, has 291 aa. The predicted protein corresponding to POU1F1β, also named PIT-1.a or PIT-1β, has 317 aa and acts as a repressor in pituitary cells (Theill et al., 1992; Jonsen et al., 2009). POU1F1 is structurally related to the POU family of transcriptional regulators, containing a characteristic POU domain divided into two regions, the POU-specific and homeo subdomains. The POUs-specific domain consists of 75 amino acids, comprises 4 α-helices, and contributes to the DNA binding specificity and protein / protein interactions (Ingraham et al., 1990; Jacobson et al., 1997). The homeodomain is composed of 60 amino and contains 3 α-helices. The N-terminal part of POU1F1 is involved in the transcriptional activity. POU1F1 binds as a dimer to most DNA response elements (for review see Phillips and Luisi, 2000).

The expression of POU1F1 is largely restricted in the pituitary gland in somato- thyreo- and lacto-trope cells, but this factor is also expressed in some extrapituitary tissues and cell lines, including the mammary gland (Gil-Puig et al., 2002).

The localization of POU1F1 is nuclear.

POU1F1 is a member of the POU family of transcription factors. This factor is required for terminal differentiation of the somatotrope, lactotrope and thyrotrope cell types (Ingraham et al., 1988; Cohen et al., 1996). This factor is also implicated in the cell growth and prevents the apoptotic cell death (Pellegrini et al., 2006).

In humans, mutation in the POU1F1 gene has been shown to be responsible for combined pituitary hormone deficiency (for review see Quentien et al., 2006) (see below).