Maternal mRNAs are translationally regulated during early development. Zar1 and its closely related homolog, Zar2, are both crucial in early development. Xenopus laevis Zygote arrest 2 (Zar2) binds to the Translational Control Sequence (TCS) in maternal mRNAs and regulates translation. The molecular mechanism of Zar1 has not been described. Here we report similarities and differences between Xenopus Zar1 and Zar2. Analysis of Zar sequences in vertebrates revealed two Zar family members with conserved, characteristic amino acid differences in the C-terminal domain. The presence of only two vertebrate Zar proteins was supported by analyzing Zar1 synteny. We propose that the criteria for naming Zar sequences are based on the characteristic amino acids and the chromosomal context. We also propose reclassification of some Zar sequences. We found that Zar1 is expressed throughout oogenesis and is stable during oocyte maturation. The N-terminal domain of Zar1 repressed translation of a reporter construct in immature oocytes. Both Zar1 and Zar2 bound to the TCS in the Wee1 and Mos 3′ UTRs using a zinc finger in the C-terminal domain. However, Zar1 had much higher affinity for RNA than Zar2. To show the functional significance of the conserved amino acid substitutions, these residues in Zar2 were mutated to those found in Zar1. We show that these residues contributed to the different RNA binding characteristics of Zar1 compared to Zar2. Our study shows that Zar proteins have generally similar molecular functions in the translational regulation of maternal mRNAs, but they may have different roles in early development.
Harlequin Ichthyosis is a severe skin disease caused by mutations in the human gene encoding ABCA12. Here, we characterize a novel mutation in intron 29 of the mouse Abca12 gene that leads to the loss of a 5’ splice donor site and truncation of the Abca12 RNA transcript. Homozygous mutants of this smooth skin or smsk allele die perinatally with shiny translucent skin, typical of animal models of Harlequin Ichthyosis. Characterization of smsk mutant skin showed that the delivery of glucosylceramides and CORNEODESMOSIN was defective, while ultrastructural analysis revealed abnormal lamellar bodies and the absence of lipid lamellae in smsk epidermis. Unexpectedly, mutant stratum corneum remained intact when subjected to harsh chemical dissociation procedures. Moreover, both KALLIKREIN 5 and -7 were drastically decreased, with retention of desmoplakin in mutant SC. In cultured wild type keratinocytes, both KALLIKREIN 5 and -7 colocalized with ceramide metabolites following calcium-induced differentiation. Reducing the intracellular levels of glucosylceramide with a glucosylceramide synthase inhibitor resulted in decreased secretion of KALLIKREIN proteases by wild type keratinocytes, but not by smsk mutant keratinocytes. Together, these findings suggest an essential role for ABCA12 in transferring not only lipids, which are required for the formation of multilamellar structures in the stratum corneum, but also proteolytic enzymes that are required for normal desquamation. Smsk mutant mice recapitulate many of the pathological features of HI and can be used to explore novel topical therapies against a potentially lethal and debilitating neonatal disease.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.