title: Selective constraints on the activation domain of transcription factor Pit-1.
abstract: The POU transcription factor Pit-1 activates members of the prolactin/growth hormone gene family in specific endocrine cell types of the pituitary gland. Although Pit-1 is structurally conserved among vertebrate species, evolutionary changes in the pattern of Pit-1 RNA splicing have led to a notable "contraction" of the transactivation domain in the mammalian lineage, relative to Pit-1 in salmonid fish. By site-directed mutagenesis we demonstrate that two splice insertions in salmon Pit-1, called beta (29 aa) and gamma (33 aa), are critical for cooperative activation of the salmon prolactin gene. Paradoxically, Pit-1-dependent activation of the prolactin gene in rat is enhanced in the absence of the homologous beta-insert sequence. This apparent divergence in the mechanism of activation of prolactin genes by Pit-1 is target gene specific, as activation of rat and salmon growth hormone genes by Pit-1 splice variants is entirely conserved. Our data suggest that efficient activation of the prolactin gene in the vertebrate pituitary has significantly constrained the pattern of splicing within the Pit-1 transactivation domain. Rapid evolutionary divergence of prolactin gene function may have demanded changes in Pit-1/protein interactions to accommodate new patterns of transcriptional control by developmental or physiological factors.
authors.affiliation: Department of Clinical Biochemistry, University of Toronto, ON Canada.
authors.forename: S
authors.initials: S
authors.lastname: Majumdar
authors.forename: D M
authors.initials: DM
authors.lastname: Irwin
authors.forename: H P
authors.initials: HP
authors.lastname: Elsholtz
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D005075:Biological Evolution; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D014644:Genetic Variation; D008322:Mammals; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010902:Pituitary Gland / Q000378:metabolism*; D014176:Protein Biosynthesis; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012474:Salmon; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014714:Vertebrates
chemical_list: D004268:DNA-Binding Proteins; C494186:Pou1f1 protein, rat; D011994:Recombinant Proteins; D050817:Transcription Factor Pit-1; D014157:Transcription Factors