ALDH4A1 genes encode mitochondrial enzymes of delta-1-pyrroline-5-carboxylate metabolism, generating glutamate from either proline or ornithine. Analyses were undertaken of several vertebrate and invertebrate genomes using reported human and mouse ALDH4A1 amino acid sequences. ALDH4A1 sequences and structures were highly conserved, including residues involved in catalysis, coenzyme binding and enzyme structure, previously reported for mouse and human ALDH4A1. The human ALDH4A1 gene contained 15 coding exons and was more highly expressed in human liver and kidney cortex. Vertebrate ALDH4A1 mitochondrial leader sequences exhibited diverse sequences. Phylogeny studies supported the appearance of the ALDH4A1 gene in invertebrate evolution which has been conserved and retained throughout subsequent vertebrate evolution as a single ALDH4A1 gene. Exceptions included polyploidy observed for the Atlantic salmon (Salmo salar) and African toad (Xenopus laevis) genes. An examination of ALDH4A1 sequences from related Drosophila species supported the appearance of a second ALDH4A gene (ALDH4A2) and time dependent evolutionary changes over the past 50 million years for both genes.

At least 19 human aldehyde dehydrogenase (ALDH) genes and enzymes have been studied among vertebrate organisms. BLAT and BLAST analyses were undertaken of Xenopus tropicalis (western clawed frog) and Xenopus laevis (African clawed frog) genomes which are related diploid (N = 20) and allotetraploid (N = 36) species, respectively. The corresponding ALDH genes and proteins within these Xenopus genomes were identified and studied. Evidence is presented for tetraploid copies of 10 Xenopus laevis ALDH genes, whereas another 7 identified ALDH genes were diploid in nature. Xenopus laevis and Xenopus tropicalis ALDH amino acid sequences were highly homologous with the human enzymes, with the exception of the mitochondrial signal peptide sequences. Amino acids performing catalytic and structural roles were conserved and identified based on previous reports of 3D structures for the corresponding mammalian enzymes.

At least fifteen families of mammalian carbonic anhydrases (CA) (E.C. 4.2.1.2) catalyse the hydration of carbon dioxide and related functions. CA5A and CA5B genes encode distinct mitochondrial enzymes and perform essential biochemical roles, including ammonia detoxification and glucose metabolism. Bioinformatic methods were used to predict the amino acid sequences, secondary structures and gene locations for CA5A and CA5B genes and proteins using data from vertebrate genome projects. CA5A and CA5B genes usually contained 7 coding exons for each of the vertebrate genomes examined. Human CA5A and CA5B subunits contained 305 and 317 amino acids, respectively, with key amino acid residues including mitochondrial transit peptides; three Zinc binding sites (His130, His132, His155); and a Tyr164 active site. Phylogenetic analyses of vertebrate CA5 gene families suggested that it is an ancient gene in vertebrate evolution which had undergone a gene duplication event in a mammalian ancestral genome forming the CA5A and CA5B gene families in monotreme, marsupial and eutherian mammals. CA5A was predominantly expressed in liver whereas CA5B had a wide tissue distribution profile, was localized on the X-chromosome and was more highly conserved during mammalian evolution.

Bioinformatic analyses of salmon (Salmo salar) ALDH amino acid sequences supported the presence of at least 30 ALDH genes, which is more than for any other higher vertebrate and is greater than the 19 human ALDH genes currently reported. These included 8 polyploid ALDH genes and proteins: ALDH1A2 (chromosomes 11 and 26); ALDH1L2 (chromosomes 7 and 17); ALDH2, encoding mitochondrial ALDH2 (chromosomes 2 and 5); ALDH3A2 (chromosomes 4, 9 and 20), for which evidence for 5 genes was obtained; ALDH3B1 (chromosomes 3, 6 and 24); ALDH4A1 (chromosomes 12 and 22); ALDH6A1 (chromosomes 1, 6 and 15); and ALDH18A1 (chromosomes 19 and 28). In contrast, 7 salmon ALDH gene families (ALDH1A1, ALDH1A3, ALDH5, ALDH7, ALDH8, ALDH9 and ALDH16) possessed only one gene family member. Phylogenetic studies of salmon and rainbow trout ALDH3A2 genes and proteins suggested that salmonid gene tetraploidy has occurred in at least 2 distinct stages of ALDH3A2 gene evolution.

Ceramide synthase 6 (CerS6, also known as LASS6) is one of the six members of ceramide synthase gene family in humans. Comparisons of CerS6 amino acid sequences and structures as well as of CerS6 gene structures/locations were conducted using data from several vertebrate genome projects. A specific role for the CerS6 gene and protein has been identified as the endoplasmic reticulum C14- and C16-ceramide synthase. Mammalian CerS6 proteins share 90–100% similarity among different species, but are only 22–63% similar to other CerS family members, suggesting that CerS6 is a distinct gene family. Sequence alignments, predicted transmembrane, lumenal and cytoplasmic segments and N-glycosylation sites were also investigated, resulting in identification of the key conserved residues, including the active site as well as C-terminus acidic and serine residues. Mammalian CerS6 genes contain ten exons, are primarily located on the positive strands and transcribed as two major isoforms. The human CERS6 gene promoter harbors a large CpG island (94 CpGs) and multiple transcription factor binding sites (TFBS), which support precise transcriptional regulation and signaling functions. Additional regulation is conferred by 15 microRNA (miRNA) target sites identified in the CERS6 3′-UTR region. Phylogenetic analysis of the vertebrate CerS1–6 gene families relationships supports a major role for the CerS6 enzyme that is strongly conserved throughout vertebrate evolution.

Arylsulfatase K (ARSK) is one of 17 sulfatase gene family members encoded on the human genome for which a role has been recently identified as a lysosomal 2-sulfoglucuronate sulfatase.Vertebrate ARSK sequences shared 60-82% identity but only <27% identities with other arylsulfatase family members.Comparative enzyme structures were studied, including residues with predicted roles in forming N-glycosylation sites, Ca 2+ binding and active site residues.Vertebrate ARSK genes usually contained 8 coding exons.A human ARSK gene promoter comprised CpG61 and multiple TFBS, which may be involved in signal transduction, transcription activation or regulating entry into cell division.Phylogenetic analyses examined evolutionary changes for the vertebrate ARSK and the invertebrate SUL1 genes.In summary, a major role for this enzyme as a 2-sulfoglucuronate sulfatase is supported which has been conserved throughout vertebrate evolution.

Glutamyl aminopeptidase (ENPEP) is a member of the M1 family of endopeptidases which are mammalian type II integral membrane zinc-containing endopeptidases. ENPEP is involved in the catabolic pathway of the renin-angiotensin system forming angiotensin III, which participates in blood pressure regulation and blood vessel formation. Comparative ENPEP amino acid sequences and structures and ENPEP gene locations were examined using data from several mammalian genome projects. Mammalian ENPEP sequences shared 71-98% identities. Five N-glycosylation sites were conserved for all mammalian ENPEP proteins examined although 9-18 sites were observed, in each case. Sequence alignments, key amino acid residues and predicted secondary and tertiary structures were also studied, including transmembrane and cytoplasmic sequences and active site residues. Highest levels of human ENPEP expression were observed in the terminal ileum of the small intestine and in the kidney cortex. Mammalian ENPEP genes contained 20 coding exons. The human ENPEP gene promoter and first coding exon contained a CpG island (CpG27) and at least 6 transcription factor binding sites, whereas the 3'-UTR region contained 7 miRNA target sites, which may contribute to the regulation of ENPEP gene expression in tissues of the body. Phylogenetic analyses examined the relationships of mammalian ENPEP genes and proteins, including primate, other eutherian, marsupial and monotreme sources, using chicken ENPEP as a primordial sequence for comparative purposes.

Extracellular sulfatases (SULF1; SULF2) (EC: 3.1.6.-) are members of the sulfatase enzyme family which exhibit endoglucosamine-6-sulfatase activity and carry out essential roles in proteoglycan metabolism. These enzymes regulate a number of critical signalling pathways and the sulfation state of glycoaminoglycans in the extracellular space. SULF1 and SULF2 amino acid sequences and structures and SULF-like gene locations were examined using bioinformatic data from several genome projects. Sequence alignments and conserved secondary structures and key amino acid residues and domains were studied. Comparative genomic analyses were conducted using the UC Santa Cruz Genome Browser. Phylogeny studies investigated the evolutionary relationships of these genes and proteins. Human and other vertebrate SULF1 and SULF2 sequences were conserved, including signal peptides, metal (Ca2+) and substrate binding sequences, active site residues and N-glycosylation sites (sulfatase domain); and a C-terminal positively charged hydrophilic domain. Predicted 2D structures were identified for the sulfatase domain of vertebrate SULF1 and SULF2 using a bacterial phosphatase structure (PDB:4UPK). Vertebrate SULF1 and SULF2 genes usually contained 18/19 or 20 coding exons, respectively. Transcription factor binding sites and miR-binding sites were identified within the human SULF1 and SULF2 gene promoters and 3’-UTR regions, respectively. The Estrogen Receptor Gene (ESR1) was identified in the SULF2 promoter which may contribute to the higher expression level for this gene in female reproductive tissues. SULF1 and SULF2 genes and proteins were present in all vertebrate genomes examined. Phylogenetic analyses suggested that an ancestral invertebrate SUL1 gene underwent a gene duplication event to form two separate lines of vertebrate gene evolution: SULF1 and SULF2.

IDS is responsible for the lysosomal degradation of heparan sulfate and dermatan sulfate and linked to an X-linked lysosomal storage disease, mucopolysaccharidosis 2 (MPS2), resulting in neurological damage and early death. Comparative IDS amino acid sequences and structures and IDS gene locations were examined using data from several vertebrate genome projects. Vertebrate IDS sequences shared 60–99% identities with each other. Human IDS showed 47% sequence identity with fruit fly (Drosophila melanogaster) IDS. Sequence alignments, key amino acid residues, N-glycosylation sites and conserved predicted secondary and tertiary structures were also studied, including signal peptide, propeptide and active site residues. Mammalian IDS genes usually contained 9 coding exons. The human IDS gene promoter contained a large CpG island (CpG46) and 5 transcription factor binding sites, whereas the 3′-UTR region contained 5 miRNA target sites. These may contribute to IDS gene regulation of expression in the brain and other neural tissues of the body. An IDS pseudogene (IDSP1) was located proximally to the IDS gene on the X-chromosome in primate genomes. Phylogenetic analyses examined the relationships and potential evolutionary origins of the vertebrate IDS gene. These suggested that IDS has originated in an invertebrate ancestral genome and retained throughout vertebrate evolution and conserved on marsupial and eutherian X-chromosomes, with the exception of rat Ids on chromosome 8.

At least 19 sulfatase genes have been reported on the human genome, including four arylsulfatase (ARS) genes (ARSD; ARSE; ARSF; ARSH) and a sterylsulfatase (STS) gene located together on the X-chromosome. Bioinformatic analyses of mammalian genomes were undertaken using known human STS and ARS amino acid sequences to study the evolution of these genes and proteins encoded on eutherian and marsupial genomes. Several domain regions and key residues were conserved including signal peptides, active site residues, metal (Ca2+) and substrate binding sequences, transmembranes and N-glycosylation sites. Phylogenetic analyses describe the relationships and potential origins of these genes during mammalian evolution. Primate ARSH enzymes lacked signal peptide sequences which may influence their biological functions. CpG117 and CpG92 were detected within the 5 ' region of the human STS and ARSD genes, respectively, and miR-205 within the 3 '-UTR for the human STS gene, using bioinformatic methods A proposal is described for a primordial invertebrate STS-like gene serving as an ancestor for unequal cross over events generating the gene complex on the eutherian mammalian X-chromosome. (C) 2017 Elsevier Ltd. All rights reserved.

Multiple sulfatase genes have been reported on the human genome, including Arylsulfatase B (ARSB), Arylsulfatase I (ARSI) and Arylsulfatase J (ARSJ). ARSB is localized in lysosomes and catalyses the hydrolysis of chondroitin and dermatan sulfate groups. Bioinformatic analyses of vertebrate genomes were undertaken using known human ARSB, ARSI and ARSJ amino acid sequences to study the relatedness and evolution of these genes and proteins. Several domain regions and key residues were conserved including signal peptides, active site residues, metal (Ca2+) and substrate binding sequences, disulfide linkages and N-glycosylation sites. The genes were widely expressed in human tissues with highest levels in esophagus (ARSB), lung (ARSI) and fibroblast cells (ARSB). Human ARSB was larger in size (>200 kb) and contained 8 coding exons, whereas ARSI and ARSJ contained only 2 coding exons among all vertebrate genomes examined. CpG islands were located within the 5’ region of the human ARSB, ARSI and ARSJ genes. In addition, six and seven miR-binding sites were observed within the 3’-UTR of human ARSB and ARSJ genes, respectively. Phylogenetic analyses describe a proposal for a primordial invertebrate SUL-3 gene serving as an ancestor for unequal cross over events generating these three genes in vertebrate genomes.

Vertebrate ALDH18A1 genes encode a bifunctional mitochondrial enzyme, catalyzing a 2-step conversion of glutamate to glutamyl semialdehyde, subsequently converted into proline, ornithine and arginine. Bioinformatic analyses of vertebrate and invertebrate genomes were undertaken using known ALDH18A1 amino acid sequences. G5K (glutamyl kinase) and GPR (glutamyl phosphate reductase) domain sequences were identified for all vertebrate and invertebrate genomes examined, whereas bacterial sequences encoded separate enzymes. Vertebrate ALDH18A1 (also called P5CS) sequences were highly conserved throughout vertebrate evolution. A mechanism for generating two major vertebrate ALDH18A1 isoforms is proposed with 'a' isoform containing Asn239-Val240 with wide tissue expression, whereas the 'b' isoform lacking the dipeptide has been reported in gut tissues. Phylogenetic analyses describe the relationships and potential origins of the ALDH18A1 gene during vertebrate and invertebrate evolution and a proposal for generating the bifunctional vertebrate and invertebrate ALDH18A1 gene from a bacterial operon (proBA) encoding G5K and GPR. A more recent Aldh18a1 gene duplication event has apparently occurred with a primordial rat genome.

Inorganic pyrophosphatase (PPA; PPase) (EC: 3.6.1.1)is a member of the diphosphatase enzyme family which functions as a diphosphate hydrolase within the cytoplasm (PPA1) and mitochondria (PPA2) of vertebrate tissues.PPA1 and PPA2 amino acid sequences and structures and PPA-like gene locations were examined using bioinformatic data from several genome projects.Sequence alignments and key conserved amino acid residues were also studied (human PPA2 residues identified): the mitochondrial signal peptide (1-31); and active site residues responsible for Mg 2+ binding (164Asp, 169Asp and 201Asp), substrate binding (127Arg) and serving as the proton donor site (138Tyr).Predicted 2D and 3D structures were identified for vertebrate PPA1 and PPA2 using the reported yeast PPA1 structure (PDB: 1E9G).Vertebrate PPA1 and PPA2 genes usually contained 11 or 12 coding exons, respectively, with an extended exon 1 and an additional exon 3 observed for vertebrate PPA2 genes.Transcription factor binding sites and CpG104 were identified within the human PPA2 gene promoter; and MiR-590 for the PPA2 3'UTR.Phylogenetic analyses suggested that an ancestral invertebrate PPA gene underwent a gene duplication event to form 2 separate lines of vertebrate gene evolution: PPA1 and PPA2.

SLC9B genes and proteins are members of the sodium/lithium hydrogen antiporter family which function as solute exchangers within cellular membranes of mammalian tissues. SLC9B2 and SLC9B1 amino acid sequences and structures and SLC9B-like gene locations were examined using bioinformatic data from several vertebrate genome projects. Vertebrate SLC9B2 sequences shared 56-98% identity as compared with ∼50% identities with mammalian SLC9B1 sequences. Sequence alignments, key amino acid residues and conserved predicted transmembrane structures were also studied. Mammalian SLC9B2 and SLC9B1 genes usually contained 11 or 12 coding exons with differential tissue expression patterns: SLC9B2, broad tissue distribution; and SLC9B1, being testis specific. Transcription factor binding sites and CpG islands within the human SLC9B2 and SLC9B1 gene promoters were identified. Phylogenetic analyses suggested that SLC9B1 originated in an ancestral marsupial genome from a SLC9B2 gene duplication event.

Vertebrate ALDH1A-like genes encode cytosolic enzymes capable of metabolizing all-trans-retinaldehyde to retinoic acid which is a molecular 'signal' guiding vertebrate development and adipogenesis. Bioinformatic analyses of vertebrate and invertebrate genomes were undertaken using known ALDH1A1, ALDH1A2 and ALDH1A3 amino acid sequences. Comparative analyses of the corresponding human genes provided evidence for distinct modes of gene regulation and expression with putative transcription factor binding sites (TFBS), CpG islands and micro-RNA binding sites identified for the human genes. ALDH1A-like sequences were identified for all mammalian, bird, lizard and frog genomes examined, whereas fish genomes displayed a more restricted distribution pattern for ALDH1A1 and ALDH1A3 genes. The ALDH1A1 gene was absent in many bony fish genomes examined, with the ALDH1A3 gene also absent in the medaka and tilapia genomes. Multiple ALDH1A1-like genes were identified in mouse, rat and marsupial genomes. Vertebrate ALDH1A1, ALDH1A2 and ALDH1A3 subunit sequences were highly conserved throughout vertebrate evolution. Comparative amino acid substitution rates showed that mammalian ALDH1A2 sequences were more highly conserved than for the ALDH1A1 and ALDH1A3 sequences. Phylogenetic studies supported an hypothesis for ALDH1A2 as a likely primordial gene originating in invertebrate genomes and undergoing sequential gene duplication to generate two additional genes, ALDH1A1 and ALDH1A3, in most vertebrate genomes.

Cytosolic and mitochondrial 10-formyltetrahydrofolate dehydrogenases are products of separate genes in vertebrates but only one such gene is present in invertebrates. There is a significant degree of sequence similarity between the two enzymes due to an apparent origin of the gene for the mitochondrial enzyme (ALDH1L2) from the duplication of the gene for the cytosolic enzyme (ALDH1L1). The primordial ALDH1L gene originated from a natural fusion of three unrelated genes, one of which was an aldehyde dehydrogenase. Such structural organization defined the catalytic mechanism of these enzymes, which is similar to that of aldehyde dehydrogenases. Here we report the analysis of ALDH1L1 and ALDH1L2 genes from different species and their phylogeny and evolution. We also performed sequence and structure comparison of ALDH1L enzymes possessing aldehyde dehydrogenase catalysis to those lacking this feature in an attempt to explain mechanistic differences between cytoplasmic ALDH1L1 and mitochondrial ALDH1L2 enzymes and to better understand their functional roles.

Vertebrate ALDH2 genes encode mitochondrial enzymes capable of metabolizing acetaldehyde and other biological aldehydes in the body. Mammalian ALDH1B1, another mitochondrial enzyme sharing 72% identity with ALDH2, is also capable of metabolizing acetaldehyde but has a tissue distribution and pattern of activity distinct from that of ALDH2. Bioinformatic analyses of several vertebrate genomes were undertaken using known ALDH2 and ALDH1B1 amino acid sequences. Phylogenetic analysis of many representative vertebrate species (including fish, amphibians, birds and mammals) indicated the presence of ALDH1B1 in many mammalian species and in frogs (Xenopus tropicalis); no evidence was found for ALDH1B1 in the genomes of birds, reptiles or fish. Predicted vertebrate ALDH2 and ALDH1B1 subunit sequences and structures were highly conserved, including residues previously shown to be involved in catalysis and coenzyme binding for human ALDH2. Studies of ALDH1B1 sequences supported the hypothesis that the ALDH1B1 gene originated in early vertebrates from a retrotransposition of the vertebrate ALDH2 gene. Given the high degree of similarity between ALDH2 and ALDH1B1, it is surprising that individuals with an inactivating mutation in ALDH2 (ALDH2∗2) do not exhibit a compensatory increase in ALDH1B1 activity. We hypothesized that the similarity between the two ALDHs would allow for dominant negative heterotetramerization between the inactive ALDH2 mutants and ALDH1B1. Computational-based molecular modeling studies examining predicted protein–protein interactions indicated that heterotetramerization between ALDH2 and ALDH1B1 subunits was highly probable and may partially explain a lack of compensation by ALDH1B1 in ALDH2∗2 individuals.

Endothelin-converting enzyme-like 1 (ECEL1) is a member of the M13 family of neutral endopeptidases which play an essential role in the neural regulation of vertebrate respiration. Genetic deficiency of this protein results in respiratory failure soon after birth. Comparative ECEL1 amino acid sequences and structures and ECEL1 gene locations were examined using data from several vertebrate genome projects. Vertebrate ECEL1 sequences shared 66%–99% identity as compared with 30%–63% sequence identities with other M13-like family members, ECE1, ECE2, and NEP (neprilysin or MME). Three N-glycosylation sites were conserved among most vertebrate ECEL1 proteins examined. Sequence alignments, conserved key amino acid residues, and predicted secondary and tertiary structures were also studied, including cytoplasmic, transmembrane, and luminal sequences and active site residues. Vertebrate ECEL1 genes usually contained 18 exons and 17 coding exons on the negative strand. Exons 1 and 2 of the human ECEL1 gene contained 5'-untranslated (5'-UTR) regions, a large CpG island (CpG256), and several transcription factor binding sites which may contribute to the high levels of gene expression previously reported in neural tissues. Phylogenetic analyses examined the relationships and potential evolutionary origins of the vertebrate ECEL1 gene with six other vertebrate neutral endopeptidase M13 family genes. These suggested that ECEL1 originated in an ancestral vertebrate genome from a duplication event in an ancestral neutral endopeptidase M13 -like gene. Keywords: vertebrates, amino acid sequence, ECEL1, ECE1, ECE2, KELL, NEP, NEPL1, PHEX, evolution

KELL is a member of the M13 family of type II neutral endopeptidases, which functions as a blood group antigen in human and animal populations.KELL amino acid sequences and structures and KEL gene locations were examined using bioinformatic data from several mammalian genome projects.Mammalian KELL sequences shared 55-99% identity, as compared with 21-31% sequence identities with other M13-like family members.Four predicted N-glycosylation sites were conserved among the mammalian KELL proteins examined.Sequence alignments, key amino acid residues and conserved predicted secondary and tertiary structures were also studied, including active site residues, predicted disulfide forming Cys residues, cytoplasmic, transmembrane and extracellular sequences and KELL C-terminus amino acid sequences.Mammalian KEL genes usually contained 18 or 19 coding exons on the direct strand.Transcription factor binding sites within the human KEL promoter may regulate transcription within erythroid cells.Phylogenetic analyses examined the relationships and potential evolutionary origins of the mammalian KEL gene with six other vertebrate neutral endopeptidase M13 family genes.These suggested that KEL originated in an ancestral marsupial genome from a gene duplication event of a neutral endopeptidase M13-like gene.

Background: Pancreatic lipase (PTL) functions in the presence of colipase in the hydrolysis of emulsified fats in the small intestine following secretion from the pancreas.Pancreatic lipase related protein 1 (PLR1) is also found in pancreatic secretions and may perform a regulatory role in lipolysis; PLR2 catalyses pancreatic triglyceride and galactolipase reactions while PLR3 may serve a related but unknown lipase function.Comparative PTL, PLR1, PLR2 and PLR3 amino acid sequences and structures and gene locations and sequences were examined using data from several vertebrate genome projects.Methods: Sequence alignments and conserved predicted secondary and tertiary structures were studied and key amino acid residues and domains identified based on previous reports on human and pig PTL.Comparative analyses of vertebrate PTL-like genes were conducted using the UC Santa Cruz Genome Browser.Phylogeny studies investigated the evolution of these vertebrate PTL-like genes.Data: Human and mouse PTL sequences shared 78% identities but only 64-68% identities with human and mouse PLR1 and PLR2 sequences.Several vertebrate PTL and PTL-like protein domains were predicted using bioinformatics including an N-signal peptide; N-glycosylation site(s); an α/β hydrolase fold region containing a catalytic triad; a 'lid' region for the active site; a 'hinge' separating the lipase and PLAT regions; and a C-terminal PLAT region.Eutherian mammalian PLR1 sequences retained residues (196Val/198Ala) responsible for the loss of triacylglycerol lipase activity whereas lower vertebrate PLR1 sequences retained the 'active' lipase residues.In contrast, mammalian PTL, PLR2 and PLR3 sequences exhibited lipase 'active' residues (196Ala/198Pro); chicken and frog PLR1 sequences retained the lipase 'active' residues; and opossum and platypus PLR1 sequences exhibited 196Ala/Ser198 and 196Ser/198Pro residues.A phylogenetic tree analysis provided evidence for four distinct vertebrate PTL-like gene families.Conclusions: Pancreatic lipase (PTL) and related genes and proteins (PLR1 and PLR2) are present in all vertebrate genomes examined whereas PLR3 is found only in primate genomes.The 'inactive' form of vertebrate PLR1 is restricted to eutherian mammals.Vertebrate PTL-like genes apparently originated in a vertebrate ancestor following gene duplication events of an ancestral PTL-like ancestral gene.Two separate lines of PTL-like gene evolution are proposed in lower vertebrates (PTL/PLR1 and PLR2), with a further gene duplication event (PLR2/PLR3) for primate genomes.