The Phosphate Transporter PiT1 (Slc20a1) Revealed As a New Essential Gene for Mouse Liver Development

Abstract

Background PiT1 (or SLC20a1) encodes a widely expressed plasma membrane protein functioning as a high-affinity Na+-phosphate (Pi) cotransporter. As such, PiT1 is often considered as a ubiquitous supplier of Pi for cellular needs regardless of the lack of experimental data. Although the importance of PiT1 in mineralizing processes have been demonstrated in vitro in osteoblasts, chondrocytes and vascular smooth muscle cells, in vivo evidence is missing.Methodology/Principal FindingsTo determine the in vivo function of PiT1, we generated an allelic series of PiT1 mutations in mice by combination of wild-type, hypomorphic and null PiT1 alleles expressing from 100% to 0% of PiT1. In this report we show that complete deletion of PiT1 results in embryonic lethality at E12.5. PiT1-deficient embryos display severely hypoplastic fetal livers and subsequent reduced hematopoiesis resulting in embryonic death from anemia. We show that the anemia is not due to placental, yolk sac or vascular defects and that hematopoietic progenitors have no cell-autonomous defects in proliferation and differentiation. In contrast, mutant fetal livers display decreased proliferation and massive apoptosis. Animals carrying two copies of hypomorphic PiT1 alleles (resulting in 15% PiT1 expression comparing to wild-type animals) survive at birth but are growth-retarded and anemic. The combination of both hypomorphic and null alleles in heterozygous compounds results in late embryonic lethality (E14.5–E16.5) with phenotypic features intermediate between null and hypomorphic mice. In the three mouse lines generated we could not evidence defects in early skeleton formation.Conclusion/SignificanceThis work is the first to illustrate a specific in vivo role for PiT1 by uncovering it as being a critical gene for normal developmental liver growth.

Identification of a Novel Transport-independent Function of PiT1/SLC20A1 in the Regulation of TNF-induced Apoptosis

“…The broad mRNA distribution of PiT1 and PiT2 in mammalian tissues and organs has led to the proposal that PiT1 and PiT2 could serve a housekeeping role in P i homeostasis (4,6) and provide cells with their basic P i needs. However, the knock-out of PiT1 in mice (by two different groups, including ours (7,8)) revealed an unexpected phenotype. Homozygous deletion of PiT1 resulted in embryonic lethality at embryonic day 12.5 (7).…”

“…However, the knock-out of PiT1 in mice (by two different groups, including ours (7,8)) revealed an unexpected phenotype. Homozygous deletion of PiT1 resulted in embryonic lethality at embryonic day 12.5 (7). Further investigations showed that PiT1 is an essential gene for liver development (7).…”

“…Homozygous deletion of PiT1 resulted in embryonic lethality at embryonic day 12.5 (7). Further investigations showed that PiT1 is an essential gene for liver development (7). PiT1-deficient embryos displayed hypoplastic fetal livers and subsequent reduced hematopoiesis, resulting in severe anemia and death.…”

Phosphate Transport Kinetics and Structure-Function Relationships of SLC34 and SLC20 Proteins

“…For example, loss of function mutations in the PiT-2 gene were reported that are implicated in disturbed brain P i homeostasis (familial idiopathic basal ganglia calcification) (Wang, Li et al 2012). Furthermore, a PiT-1-/-mouse was reported to be embryonic fatal, which suggested a critical role for PiT-1 in liver development (Beck, Leroy et al 2010). …”

Identification of SLC20A1 and SLC15A4 among other genes as potential risk factors for combined pituitary hormone deficiency

“…32 A Slc20a1 knockout mouse is embryonically lethal. 33 We have identified two SLC20A1 variants, L89S and L521F, with high CADD scores in two unrelated individuals ( Table 2). The variants reside in exon 1 and exon 7 in positions that are highly conserved between vertebrates; L521F was even conserved down to Drosophila.…”