Identification and characterization of transcript variants of chicken peroxisome proliferator-activated receptor gamma

Abstract

Peroxisome proliferator-activated receptor gamma regulates adipogenesis. The genomic structure of the chicken peroxisome proliferator-activated receptor gamma (cPPARγ) gene has not been fully characterized, and only one cPPARγ gene mRNA sequence has been reported in genetic databases. Using 5' rapid amplification of cDNA ends, we identified five different cPPARγ mRNAs that are transcribed from three transcription initiation sites. The open reading frame analysis showed that these five cPPARγ transcript variants (cPPARγ1 to 5) could encode two cPPARγ protein isoforms (cPPARγ1 and cPPARγ2), which differ only in their N-terminal region. Quantitative real-time RT-PCR analysis showed that, of these five cPPARγ transcript variants, cPPARγ1 was ubiquitously highly expressed in various chicken tissues, including adipose tissue, liver, kidney, spleen and duodenal; cPPARγ2 was exclusively highly expressed in adipose tissue; cPPARγ3 was highly expressed in adipose tissue, kidney, spleen and liver; cPPARγ4 and cPPARγ5 were ubiquitously weakly expressed in all the tested tissues, and comparatively, cPPARγ5 was highly expressed in adipose tissue, heart, liver and kidney. The comparison of the expression of the five cPPARγ transcript variants showed that adipose tissue cPPARγ1 expression was significantly higher in the fat line than in the lean line from 2 to 7 wk of age (P < 0.05 or P < 0.01). Adipose tissue cPPARγ3 expression was significantly higher in the fat line than in the lean line at 3, 5 and 6 wk of age (P < 0.01, P < 0.05), but lower at 4 wk of age (P < 0.05). Adipose tissue cPPARγ5 expression was significantly higher in the fat line than in the lean line at 3, 4, and 6 wk of age (P < 0.01) and at 2 and 7 wk of age (P < 0.05). This is the first report of transcript variants and protein isoforms of cPPARγ gene. Our findings provided a foundation for future investigations of the function and regulation of cPPARγ gene in adipose tissue development.

An Upstream Open Reading Frame Represses Translation of Chicken PPARγ Transcript Variant 1

“…Herein, we focused our attention on the PPARγ1 uORF. Of these five chicken PPARγ transcript variants, PPARγ transcript variant 1 (PPARγ1) is highly expressed in various chicken tissues, including abdominal adipose, spleen, and liver (Duan et al, 2015), which is consistent with our results showing that PPARγ1 5 UTR had high reporter activity (Figures 1A,B). Unlike the other two uORF-containing 5 UTR isoforms, PPARγ1 5 UTR presented the largest uORF, and its uAUG was in a favorable Kozak consensus context.…”

“…We previously identified five different chicken PPARγ transcript variants (PPARγ 1 to 5) by 5 rapid amplification of cDNA ends (5 RACE) in chicken abdominal adipose tissue (Duan et al, 2015). These chicken PPARγ transcript variants encode two protein isoforms (PPARγ1 and PPARγ2) that differ in their N-terminal extension.…”

“…Chicken PPARγ2 contains six additional amino acids at the N-terminus compared with PPARγ1. These five chicken PPARγ transcript variants differed in 5 UTR sequence and length, and had different tissue distribution patterns (Duan et al, 2015), suggesting that 5 UTRs may play a role in the posttranscriptional regulation of PPARγ gene expression. To investigate the posttranscriptional regulatory roles of the five 5 UTR isoforms on chicken PPARγ gene expression, we constructed their respective 5 UTR reporter constructs.…”

An upstream open reading frame represses translation of chicken PPARγ transcript variant 1

“…Herein, we focused our attention on the PPARγ1 uORF. Of these five chicken PPARγ transcript variants, PPARγ transcript variant 1 (PPARγ1) is highly expressed in various chicken tissues, including abdominal adipose, spleen, and liver (Duan et al 2015), which is consistent with our results showing that PPARγ1 5′…”

“…Chicken PPARγ2 contains 6 additional amino acids at the N-terminus compared with PPARγ1. These five chicken PPARγ transcript variants differed in 5′ UTR sequence and length, and had different tissue distribution patterns (Duan et al 2015),…”