Elsevier

Gene

Volume 339, 15 September 2004, Pages 131-138
Gene

Emergence of Talanin protein associated with human uric acid nephrolithiasis in the Hominidae lineage

https://doi.org/10.1016/j.gene.2004.06.030Get rights and content

Abstract

Recently, we identified a susceptibility locus for human uric acid nephrolithiasis (UAN) on 10q21–q22 and demonstrated that a novel gene (ZNF365) included in this region produces through alternative splicing several transcripts coding for four protein isoforms. Mutation analysis showed that one of them (Talanin) is associated with UAN. We examined the evolutionary conservation of ZNF365 gene through a comparative genomic approach. Searching for mouse homologs of ZNF365 transcripts, we identified a highly conserved mouse ortholog of ZNF365A transcript, expressed specifically in brain. We did not found a mouse homolog for ZNF365D transcript encoding the Talanin protein, even if we were able to identify the corresponding genomic region in mouse and rat not yet organized in canonical gene structure suggesting that ZNF365D was originated after the branching of hominoid from rodent lineage. In mouse and in most mammals, a functional uricase degrades the uric acid to allantoin, but uricase activity was lost during the Miocene epoch in hominoids. Searching for the presence of Talanin in Primates, we found a canonical intron–exon structure with several stop codons preventing protein production in Old World and New World monkeys. In humans, we observe expression and we have evidence that ZNF365D transcript produces a functional protein. It seems therefore that ZNF365D transcript emerged during primate evolution from a noncoding genomic sequence that evolved in a standard gene structure and assumed its role in parallel with the disappearance of uricase, probably against a disadvantageous excessive hyperuricemia.

Introduction

Uric acid nephrolithiasis (UAN) is a common multifactorial disorder characterized by the presence of small crystals and stones in the urinary tract when the urine becomes overly concentrated with uric acid (Jaeger, 1996, Curhan et al., 1997). Uric acid is produced during the metabolism of purines and, in most mammals, is further degraded by the hepatic enzyme, urate oxidase (uricase), to allantoin, which is excreted in the urine. Mutations in the uricase gene in human and great apes during the Miocene epoch determined the enzyme activity disappearance (Wu et al., 1992). As a consequence, in these species, the uric acid is the end product of purine metabolism and there is an increase of its serum level: (>2 mg/dl compared with most mammals <2 mg/dl). In the past, urate was considered an inert product without any physiological value, but the observation that urate oxidase activity was inactivated by several independent mutations was interpreted as evidence of an evolutionary advantage in elevated uric acid levels (Christen et al., 1970, Wacker, 1970). Because uric acid is a powerful antioxidant that directly scavenges reactive oxygen species and chelates iron, it played an important role in protecting hominoids from oxidative damage (Ames et al., 1981, Whiteman and Halliwell, 1996). In contrast, there is evidence that hyperuricemia is commonly associated with the risk of hypertension, of cardiovascular and renal diseases (Selby et al., 1990, Jossa et al., 1994, Wu et al., 1994, Cannon et al., 1966, Alderman et al., 1999, Verdecchia et al., 2000, Johnson et al., 2003). A likely evolutionary scenario posits that a urate homeostasis system developed against an excessive and detrimental hyperuricemia that was originally advantageous. However, selective evolutionary advantages resulting from the loss of uricase and disadvantages resulting from excessive accumulation of serum uric acid levels are probably related. The identification of human genes involved in uric acid nephrolithiasis may disclose pathways of uric acid metabolism.

Recently, in a study of UAN in an ancient founder Sardinian micropopulation, we identified a novel gene (ZNF365) encoding four different protein isoforms, one of which (Talanin) is associated with the disease (OMIM 605990) (Gianfrancesco et al., 2003). In this paper, we carried out an evolutionary analysis of ZNF365 gene. In mouse, we isolated the ortholog of ZNF365A, not involved in UAN, while the transcript ZNF365D encoding the Talanin protein is not found in mouse and rat. We detected it in New and Old World monkeys as a nonfunctional gene and found its expression in hominoids. The identification of this gene and its particular evolution offers the occasion to explore the emergence of a human gene and its specific function.

Section snippets

Isolation of cDNA clones

Mouse ZNF365A-related cDNA was obtained from a mix of mouse polyA+ RNA including lung, colon, retina, and brain, by RT-PCR using primer pairs based on the mouse EST sequences. Sequence databases were searched using the BLAST sequence alignment program (Altschul et al., 1990). We designed primers in order to yield a series of overlapping fragments spanning the entire cDNA. The cDNAs were subcloned into TOPO cloning vector (Invitrogen) and analyzed by Dye-Terminator cycle sequencing on ABI Prism

Isolation of mouse homologous of human ZNF365A

In order to isolate the murine ortholog of the four different transcripts and proteins generated by alternative splicing of the human ZNF365 gene, we performed an expressed sequence tag (EST) database search to identify ESTs of mouse-related genes. A variety of mouse ESTs were detected only for ZNF365A transcript, but no sequences with significant homology to ZNF365B, ZNF365C, and ZNF365D transcripts either at nucleotide or at protein level were found. By RT-PCR using primer pairs based on

Discussion

Searching for mouse orthologs of a recently isolated human gene, associated with uric acid nephrolithiasis, we detected an interesting differential evolutionary pattern. The human gene produces through alternative splicing four different transcripts: ZNF365A, ZNF365B, ZNF365C, and ZNF365D coding for different protein isoforms. We found that ZNF365A has a high homology with a mouse-related gene (Znf365A) while ZNF365B, ZNF365C, and ZNF365D are absent in rodents. Human, mouse, and rat genomic

References (27)

  • G.C. Curhan et al.

    Family history and risk of kidney stones

    J. Am. Soc. Nephrol.

    (1997)
  • E.T. Dermitzakis et al.

    Numerous potentially functional but non-genic conserved sequences on human chromosome 21

    Nature

    (2002)
  • P. Jaeger

    Genetic versus environmental factors in renal stone disease

    Curr. Opin. Nephrol. Hypertens.

    (1996)
  • 1

    Present address: Institute of Food Science, CNR, Avellino, Italy.

    View full text