Deficiency of the placenta- and yolk sac-specific tristetraprolin family member ZFP36L3 identifies likely mRNA targets and an unexpected link to placental iron metabolism

Abstract

The ZFP36L3 protein is a rodent-specific, placenta-and yolk sacspecific member of the tristetraprolin (TTP) family of CCCH tandem zinc finger proteins. These proteins bind to AU-rich elements in target mRNAs, and promote their deadenylation and decay. We addressed the hypotheses that the absence of ZFP36L3 would result in the accumulation of target transcripts in placenta and/or yolk sac, and that some of these would be important for female reproductive physiology and overall fecundity. Mice deficient in ZFP36L3 exhibited decreased neonatal survival rates, but no apparent morphological changes in the placenta or surviving offspring. We found Zfp36l3 to be paternally imprinted, with profound parent-of-origin effects on gene expression. The protein was highly expressed in the syncytiotrophoblast cells of the labyrinth layer of the placenta, and the epithelial cells of the yolk sac. RNA-Seq of placental mRNA from Zfp36l3 knockout (KO) mice revealed many significantly upregulated transcripts, whereas there were few changes in KO yolk sacs. Many of the upregulated placental transcripts exhibited decreased decay rates in differentiated trophoblast stem cells derived from KO blastocysts. Several dozen transcripts were deemed high probability targets of ZFP36L3; these include proteins known to be involved in trophoblast and placenta physiology. Type 1 transferrin receptor mRNA was unexpectedly decreased in KO placentas, despite an increase in its stability in KO stem cells. This receptor is crucial for placental iron uptake, and its decrease was accompanied by decreased iron stores in the KO fetus, suggesting that this intrauterine deficiency might have deleterious consequences in later life.

Regulation of transferrin receptor-1 mRNA by the interplay between IRE-binding proteins and miR-7/miR-141 in the 3′-IRE stem–loops

“…However, it seems that Zfp36L3 expresses only in specific tissues (yolk sac and placenta) in certain rodents (rats and mice), while the IRP-IRE system is ubiquitous across vertebrates. In addition, it demonstrated that deletion of the Zfp36l3 in mice stabilized TfR1 mRNA, but counterintuitively, significantly decreased overall TfR1 mRNA expression (Stumpo et al 2016), highlighting the complexity of TfR1 expression regulation.…”

“…A recent study uncovered a role for TTP (tristetraprolin) to destabilize TfR1 mRNA (Bayeva et al 2012); however, this study concluded that TTP activity was activated by iron deficiency rather than iron excess and seems to be separate from the IRE-IRP system. A follow-up study highlighted the importance of a TTP-family protein (ZFP36L3) in TfR1 regulation during development (Stumpo et al 2016). However, it seems that Zfp36L3 expresses only in specific tissues (yolk sac and placenta) in certain rodents (rats and mice), while the IRP-IRE system is ubiquitous across vertebrates.…”

Dynamics of lineage commitment revealed by single-cell transcriptomics of differentiating embryonic stem cells

“…Expression in the long term cultured ectoderm-and XEN-like cells was compared to these tissue expression data sets from the literature: neural progenitor cells 64 , neural crest cells 65 , yolk sac 66 and a XEN cell line 67 .…”

An Ancient Family of RNA-Binding Proteins: Still Important!

“…It is the only mouse family member that appears to reside permanently in the cytoplasm, in contrast to the nucleo-cytoplasmic shuttling behavior of the other proteins. A complete KO of Zfp36l3 in mice resulted in decreased neonatal survival rates [11], as well as the accumulation of many transcripts that were stabilized in studies of trophoblastic stem cells derived from the KO mice, many of which are important for placental function.…”

“…All four of the mouse genes have been knocked out at the “whole body” level, with remarkably different phenotypes; in several cases, cell- and tissue-specific knockouts have been developed as well [11-16]. Results of these studies have pointed to important physiological roles of these proteins in processes as divergent as innate immunity, establishment of the fetal circulation, hematopoiesis, and placental physiology.…”