Identification and characterization of novel peroxisome proliferator-activated receptor-gamma (PPAR-γ) transcriptional variants in pig and human

Summary The peroxisome proliferator‐activated receptor‐gamma (PPAR‐γ) is a member of the steroid/thyroid/retinoid receptor superfamily, and is primarily expressed in fat tissue. To date, two major PPAR‐γ isoforms have been identified in pig, PPAR‐γ1 and PPAR‐γ2. Porcine PPAR‐γ1a consists of two leader exons, designated A1 and A2, followed by six exons containing the open reading frame. Here, we report the isolation and characterization of three novel PPAR‐γ1 transcripts. PPAR‐γ1b is derived from exon A1, with exon A2 spliced out. PPAR‐γ1c and PPAR‐γ1d are derived from the new exon, A′, containing exon A2 (γ1c) or without exon A2 (γ1d). Based on PCR analysis of PAC clones that included sequences from the 5′‐untranslated region of the PPAR‐γ gene, the new A′ exon is located between the known exons A1 and A2. We also isolated the human homologue to exon A′, as well as the two new PPAR‐γ1c and ‐γ1d splice variants, from human adipose tissue. Studies of the expression of porcine PPAR‐γ by real time reverse transcription‐polymerase chain reaction analysis show that transcripts derived from exon A1 were not expressed at significantly different levels in visceral fat (lamina subserosa) or subcutaneous fat (back fat, inner and outer layer). In contrast, exon A′‐derived transcripts were expressed at progressively higher levels in the inner and outer layers of subcutaneous fat than in visceral fat. The same expression pattern was also observed for PPAR‐γ2. We hypothesize that there are three promoters, which differentially regulate PPAR‐γ1 and PPAR‐γ2 gene expression, depending on the specific localization of the fat tissue.