Abstract
BackgroundMembers of the Paired-like homeodomain transcription factor (PITX) gene family, particularly PITX1 and PITX2, play important roles in normal development and in differentiated cell functions. Three major isoforms of PITX2 were previously reported to be produced through both alternative mRNA splicing (PITX2A and PITX2B) and alternative promoter usage (PITX2C). The proteins derived from these mRNAs contain identical homeodomain and carboxyl termini. Differences in the amino-termini of the proteins may confer functional differences in some contexts.ResultsHere, we report the identification of two novel PITX2 isoforms. First, we demonstrate that the Pitx2c mRNA generates two protein products, PITX2Cα and PITX2Cβ, via alternative translation initiation. Second, we identified a novel mRNA splice variant, Pitx2b2, which uses the same 5' splice donor in intron 2 as Pitx2b (hereafter referred to as Pitx2b1), but employs an alternative 3' splice acceptor, leading to an in-frame deletion of 39 base pairs relative to Pitx2b1. Pitx2b2 mRNA is expressed in both murine and human pituitary. The data show that in a murine gonadotrope cell line and adult murine pituitary what was previously thought to be PITX2B1 is actually PITX2Cβ, or perhaps PITX2B2. PITX2B1 is expressed at lower levels than previously thought. PITX2Cβ and PITX2B2 activate gonadotrope-specific gene promoter-reporters similarly to known PITX2 isoforms.ConclusionWe have identified and characterized two novel isoforms of PITX2, generated by alternative translation initiation (PITX2Cβ) and alternative mRNA splicing (PITX2B2). These proteins show similar DNA binding and trans-activation functions as other PITX2 isoforms in vitro, though their conservation across species suggests that they may play distinct, as yet unidentified, roles in vivo.
Highlights
Members of the Paired-like homeodomain transcription factor (PITX) gene family, PITX1 and PITX2, play important roles in normal development and in differentiated cell functions
Both of these proteins bound to a PITX binding site in the murine Fshb promoter in southwestern blot analysis [32], suggesting that neither product was an artifact of the expression system
We hypothesized that the Pitx2c mRNA contains alternative translation initiation codons
Summary
Members of the Paired-like homeodomain transcription factor (PITX) gene family, PITX1 and PITX2, play important roles in normal development and in differentiated cell functions. The proteins derived from these mRNAs contain identical homeodomain and carboxyl termini. PITX2 along with PITX1 and PITX3 form the PITX/RIEG subfamily of the Paired-like class of homeobox proteins [2,3,4,5,6]. PITX2 ( known as RIEG1 or ARP1) was originally cloned from a human craniofacial cDNA library and was found to be mutated in patients with Axenfeld-Rieger syndrome (ARS) [6]. The human and murine coding regions share 91% nucleotide (and 99.2% protein) sequence identity (PITX2A isoform, see more below) [3,6]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.