Cloning, Sequencing, and Expression of Selenoprotein Transcripts in the Turkey (Meleagris gallopavo)

Abstract

The minimum Se requirement for male turkey poults is 0.3 μg Se/g – three times higher than requirements found in rodents – based on liver and gizzard glutathione peroxidase-4 (GPX4) and GPX1 activities. In addition, turkey liver GPX4 activity is 10-fold higher and GPX1 activity is 10-fold lower than in rats, and both GPX1 and GPX4 mRNA levels are dramatically down-regulated by Se deficiency. Currently, the sequences of all annotated turkey selenoprotein transcripts and proteins in the NCBI database are only “predicted.” Thus we initiated cloning and sequencing of the full turkey selenoprotein transcriptome to demonstrate expression of selenoprotein transcripts in the turkey, and to develop tools to investigate Se regulation of the full selenoproteome. Total RNA was isolated from six tissues of Se-adequate adult tom turkeys, and used to prepare reverse-transcription cDNA libraries. PCR primers were designed, based initially on chicken, rodent, porcine, bovine and human sequences and later on turkey shotgun cloning sequences. We report here the cloning of full transcript sequences for 9 selenoproteins, and 3'UTR portions for 15 additional selenoproteins, which include SECIS elements in 22 3'UTRs, and in-frame Sec (UGA) codons within coding regions of 19 selenoproteins, including 12 Sec codons in SEPP1. In addition, we sequenced the gap between two contigs from the shotgun cloning of the turkey genome, and found the missing sequence for the turkey Sec-tRNA. RTPCR was used to determine the relative transcript expression in 6 tissues. GPX3 expression was high in all tissues except kidney, GPX1 expression was high in kidney, SEPW1 expression was high in heart, gizzard and muscle, and SELU expression was high in liver. SEPP2, a selenoprotein not found in mammals, was highly expressed in liver but not in other tissues. In summary, transcripts for 24 selenoproteins are expressed in the turkey, not just predicted.

The supranutritional selenium status alters blood glucose and pancreatic redox homeostasis via a modulated selenotranscriptome in chickens (Gallus gallus)

“…23 All selenoprotein genes have two characteristic features: a Secencoding TGA codon and a Sec insertion sequence (SECIS) element. 61 The alternations of these factors expression may affect selenoprotein expression. In this study, dietary supranutritional Se increased six factors signicantly at the 8 th week.…”

Selenium. Role of the Essential Metalloid in Health

“…The biosynthesis of Sec was first characterized in bacteria [22] by Böck and coworkers in the late 1980s to early 1990s [23,24], and subsequently in mammalian cells [21]. In the first step, tRNA [Ser]Sec is aminoacylated with serine, providing the carbon backbone for Sec, thus the tRNA has been designated as tRNA [Ser]Sec [21,25]. The pathway for mammalian Sec biosynthesis has been elucidated more recently, and is discussed below.…”

Selenoprotein Transcript Level and Enzyme Activity as Biomarkers for Selenium Status and Selenium Requirements in the Turkey (Meleagris gallopavo)

“…Furthermore, supernutritional-Se status (8X Se requirement) does not further up- or down-regulate any selenoprotein transcripts in rats, indicating that selenoprotein transcripts in rodents cannot be used as biomarkers of supernutritional-Se status [ 19 ]. In a previous study, we partially cloned turkey GPX1 and GPX4 mRNA and found that both were down-regulated in Se deficiency to 30% of Se-adequate levels [ 12 ], and we have now cloned and sequenced the 24 turkey selenoprotein transcripts [ 20 ], providing tools to study selenoprotein transcripts as potential biomarkers of Se status in the turkey.…”