Zebrafish mutations ingartandpaicsidentify crucial roles for de novo purine synthesis in vertebrate pigmentation and ocular development

Abstract

Although purines and purinergic signaling are crucial for numerous biochemical and cellular processes, their functions during vertebrate embryonic development have not been well characterized. We analyze two recessive zebrafish mutations that affect de novo purine synthesis, gart and paics. gart encodes phosphoribosylglycinamide formyltransferase, phosphoribosylglycinamide synthetase, phosphoribosylaminoimidazole synthetase, a trifunctional enzyme that catalyzes steps 2, 3 and 5 of inosine monophosphate (IMP) synthesis. paics encodes phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase, a bifunctional enzyme that catalyzes steps 6 and 7 of this process. Zygotic gart and paics mutants have pigmentation defects in which xanthophore and iridophore pigmentation is almost completely absent, and melanin-derived pigmentation is significantly decreased, even though pigment cells are present in normal amounts and distributions. Zygotic gart and paics mutants are also microphthalmic, resulting from defects in cell cycle exit of proliferative retinoblasts within the developing eye. Maternal-zygotic and maternal-effect mutants demonstrate a crucial requirement for maternally derived gart and paics; these mutants show more severe developmental defects than their zygotic counterparts. Pigmentation and eye growth phenotypes in zygotic gart and paics mutants can be ascribed to separable biosynthetic pathways: pigmentation defects and microphthalmia result from deficiencies in a GTP synthesis pathway and an ATP synthesis pathway, respectively. In the absence of ATP pathway activity, S phase of proliferative retinoblasts is prolonged and cell cycle exit is compromised, which results in microphthalmia. These results demonstrate crucial maternal and zygotic requirements for de novo purine synthesis during vertebrate embryonic development, and identify independent functions for ATP and GTP pathways in mediating eye growth and pigmentation, respectively.

Genetic and metabolomic analysis of AdeD and AdeI mutants of de novo purine biosynthesis: Cellular models of de novo purine biosynthesis deficiency disorders

“…In addition to its role in supplying the substrate for ADSL, PAICS is of interest because mutations in PAICS cause errors in vertebrate embryonic development [16], and because PAICS shows elevated expression in numerous cancers, and may be an important target for anticancer therapies [17], [18]. PAICS overexpression is likely due to the increased proliferation of tumor cells and consequent increased demand for purine nucleotides.…”

The role of the Mpv17 protein mutations of which cause mitochondrial DNA depletion syndrome (MDDS): lessons from homologs in different species

“…However, in tra mutants, the absence of tra function might diminish the transport of nucleotides and precursors into mitochondria of iridophores, thereby impeding mitochondrial functions with consequential apoptosis (Krauss et al, 2013). In support of this hypothesis, the tra mutant phenotype resembles that of two further zebrafish mutants, gart and paics, in which the lack of the GTP de novo synthesis results in the absence of pigmentation patterns (Ng et al, 2009). In addition, experimental support for the idea that regulated cell death is involved in the pathomechanism comes from finding vesicles resembling autophagosomes within tra mutant iridophores but not in wild type pigment cells (Krauss et al, 2013).…”

An Integrated Biochemistry and Genetics Outreach Program Designed for Elementary School Students

“…PAICS is highly conserved in higher eukaryotes, and mutations in PAICS can result in developmental defects and in some cases embryonic lethality (Tiong et al 1989;Ng et al 2009). Additionally, because cancer cells rely heavily on the de novo purine biosynthesis pathway while normal cells preferentially utilize salvage pathways (Li et al 2007), PAICS has emerged as a potential target for anticancer drugs.…”