Involvement of the eukaryotic initiation factor 6 and kermit2/gipc2 in Xenopus laevis pronephros formation

Abstract

The translation initiation factor Eif6 has been implicated as a regulator of ribosome assembly, selective mRNA translation and apoptosis. Many of these activities depend upon the phosphorylation of eif6 Serine 235 by protein kinase C (PKC). Eif6-60S is probably part of the RNAinduced silencing complex (RISC). eif6 over-expression in Xenopus embryos causes aberrant eye development. kermit2/gipc2 morphants have an eye phenotype similar to that of the eif6 overexpressors. Eye formation is regulated by insulin growth factor (IGF) signalling. eif6 interacts with the IGF receptor (IGFR) and kermit2/gipc2, which also binds to igfr. eif6 over-expression in Xenopus causes also the formation of antero-ventral oedema, suggesting a malfunction of the excretory system. Here we evaluated the pronephros phenotype. The oedema grows into the nephrocoel, expanding its boundary and is accompanied by a strong reduction of the pronephros. The three main components of the pronephros are severely impaired in eif6 over-expressors, while are not affected in eif6 morphants. Conversely, gipc2 depletion induces the oedema phenotype and reduction of the pronephros, while gipc2 overexpression does not. p110*, a constitutively active p110 subunit of the PI3 kinase partially recovers the oedema phenotype. We also determined that PKC-dependent phosphorylation of Ser235 in eif6 is not required to produce defective pronephroi. These results indicate that the levels of eif6 are highly regulated during development and instrumental for proper morphogenesis of the pronephros. Moreover, it appears that for proper pronephros development the gipc2 level should be kept within or over the physiological range and that the oedema phenotype is partly due to the inhibition of IGF signalling. KEY WORDS: pronephros, Xenopus laevis, eukaryotic initiation factor 6, kermit2/gipc2Eif6 1 (eukaryotic initiation factor 6) is a protein essential for cell survival that plays important roles in ribosome biogenesis and translation (see Ceci et al., 2003). In particular, it is associated with the plasma membrane where it interacts with b4 integrin as well as the cytoskeleton (Biffo et al., 1997). Eif6 can be regulated by extracellular signals, such as IGF (Gandin et al., 2008), and is itself a regulator of translation at the 60S ribosomal subunit. When unphosphorylated, it impedes the joining of the 60S with the 40S ribosomal subunit. When phosphorylated by PKC, Eif6 separates from the 60S subunit. As a consequence, ribosomal subunits 60S and 40S may join, allowing mRNA translation to occur (Ceci et al., 2003). Eif6-60S is probably part of the RISC (RNA-induced silencing complex) and as such may regulate the availability of mRNAs for translation (Chendrimada et al., 2007). Because EIF6 appears to act selectively on specific mRNAs (Ji Abbreviations used in this paper: Akt, serine/threonine-protein kinase; bgal, bgalactosidase; Clcnk , chloride channel Kb; cdh16 , human cadherin-16; Eif6 1 , eukaryotic initiation factor 6; IGF, insulin growth factor; Igfr, insulin g...

Early Effects of a Low Fat, Fructose-Rich Diet on Liver Metabolism, Insulin Signaling, and Oxidative Stress in Young and Adult Rats

“…Frozen 10 μm-thick sections were obtained after embedding and freezing liver fragments in Killik (Bio Optica, Milan, Italy). Sections were then stained with hematoxylin-eosin and mounted in PBS/glycerol (9:1, v/v) (Tussellino et al, 2012 ; Alwahsh et al, 2014 ). Sections were photographed with a Leica CTR 6500 UV microscope (Leica Microsystems CMS gmbH, Wetzlar, Germany) and degree of steatosis was evaluated by ImageJ software.…”

Xenopus laevis (Daudin, 1802) as a Model Organism for Bioscience: A Historic Review and Perspective

“…The ability of eif6 to control gipc2 expression is active also in the case of pronephros development, where eif6 overexpression causes edema and damage of the three main components of the pronephros. gipc2 depletion induces the edema phenotype and reduction of the pronephros constituents, as indicated by several markers, such as lhx 1 and nephrin [ 8 ]. Moreover, p110*, a constitutively active p110 subunit of pi3 kinase, corrects the abnormal kidney phenotype induced by eif6, suggesting that, similarly to the eye, eif6 may control the expression of gipc2, which is essential for pronephros morphogenesis and dependent on igf-induced akt activation [ 8 ].…”

“…This means that no approval from the health authorities is needed for in vivo experiments that involve the early stages of this species. Among the great advantages of Xenopus , there is its evolutionary closeness to higher vertebrates in terms of physiology, gene expression and organ development, such as the eyes, liver, lungs, heart, kidney and so on, thus allowing the transfer of the results directly to the human species [ 7 , 8 , 9 , 10 , 11 , 12 ]. In recent years, this model of animal species has gradually attracted the attention of ecotoxicologists and been applied in studies relating to ecotoxicology.…”

Increased expression of GIPC2 in colon adenocarcinoma is associated with a favorable prognosis and high levels of immune cell infiltration

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