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Roles of the developmental regulator unc-62/Homothorax in limiting longevity in Caenorhabditis elegans.

Van Nostrand EL, Sánchez-Blanco A, Wu B, Nguyen A, Kim SK - PLoS Genet. (2013)

Bottom Line: Through analysis of the downstream consequences of unc-62 knockdown, we identify multiple effects linked to aging.Second, unc-62 RNAi results in a broad increase in expression of intestinal genes that typically decrease expression with age, suggesting that unc-62 activity balances intestinal resource allocation between yolk protein expression and fertility on the one hand and somatic functions on the other.These results illustrate how unc-62 regulation of intestinal gene expression is responsible for limiting lifespan during the normal aging process.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Stanford University Medical Center, Stanford, California, USA.

ABSTRACT
The normal aging process is associated with stereotyped changes in gene expression, but the regulators responsible for these age-dependent changes are poorly understood. Using a novel genomics approach, we identified HOX co-factor unc-62 (Homothorax) as a developmental regulator that binds proximal to age-regulated genes and modulates lifespan. Although unc-62 is expressed in diverse tissues, its functions in the intestine play a particularly important role in modulating lifespan, as intestine-specific knockdown of unc-62 by RNAi increases lifespan. An alternatively-spliced, tissue-specific isoform of unc-62 is expressed exclusively in the intestine and declines with age. Through analysis of the downstream consequences of unc-62 knockdown, we identify multiple effects linked to aging. First, unc-62 RNAi decreases the expression of yolk proteins (vitellogenins) that aggregate in the body cavity in old age. Second, unc-62 RNAi results in a broad increase in expression of intestinal genes that typically decrease expression with age, suggesting that unc-62 activity balances intestinal resource allocation between yolk protein expression and fertility on the one hand and somatic functions on the other. Finally, in old age, the intestine shows increased expression of several aberrant genes; these UNC-62 targets are expressed predominantly in neuronal cells in developing animals, but surprisingly show increased expression in the intestine of old animals. Intestinal expression of some of these genes during aging is detrimental for longevity; notably, increased expression of insulin ins-7 limits lifespan by repressing activity of insulin pathway response factor DAF-16/FOXO in aged animals. These results illustrate how unc-62 regulation of intestinal gene expression is responsible for limiting lifespan during the normal aging process.

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UNC-62 binds age-regulated genes and modulates lifespan.(A) Adult-specific knockdown of unc-62 extends lifespan by 30%. Approximately 150 day 1 adult wild-type (N2) worms were placed on bacteria expressing dsRNA targeting either unc-62, or control bacterial containing an empty vector. The x-axis indicates days of adulthood, and the y-axis indicates the percent of worms that remain alive at that age. The lifespan assay was performed five times (p<10−5 for each assay; one representative lifespan assay is shown). See Table S2 for lifespan data. (B) Hox co-factor UNC-62 Homothorax/Meis targets in day 4 of adulthood (Young Adults) show significant overlap with age-regulated transcripts [10], [18]. Only factor-specific binding sites bound by less than 10 out of 57 transcription factors profiled by the modENCODE consortium were utilized. Enrichment p-value was determined by Fisher's Exact test. (C) Schematic of the UNC-62:GFP fosmid used to generate an UNC-62 fluorescent reporter. A GFP tag was inserted at the C-terminus of UNC-62 in a fosmid containing all unc-62 exons and introns, as well as ∼18.5 kb of 5′ promoter sequence. (D) The UNC-62:GFP fosmid-based transgene can rescue the embryonic lethality defects of both an unc-62  mutation (s472; denoted −) as well as a weaker mutation in unc-62 exon 7b (e644, denoted 7b(−)) [13]. 7b(+) refers to a transgene that expresses only the unc-62 exon 7b isoform. Circles indicate the number of viable progeny observed from 5 unmated hermaphrodites of each genotype, with the mean indicated by a horizontal line. (E) In hermaphrodites, UNC-62:GFP is expressed in intestine (int), neurons (neu), ventral nerve cord (vnc), vulval precursor cells (not shown), and (right) hypodermis (hyp). UNC-62 intestinal expression is stage-specific: intestine expression in L2 and earlier stages is weak or not visible (top), whereas intestinal expression is dramatically induced by the L4 stage (bottom).
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pgen-1003325-g001: UNC-62 binds age-regulated genes and modulates lifespan.(A) Adult-specific knockdown of unc-62 extends lifespan by 30%. Approximately 150 day 1 adult wild-type (N2) worms were placed on bacteria expressing dsRNA targeting either unc-62, or control bacterial containing an empty vector. The x-axis indicates days of adulthood, and the y-axis indicates the percent of worms that remain alive at that age. The lifespan assay was performed five times (p<10−5 for each assay; one representative lifespan assay is shown). See Table S2 for lifespan data. (B) Hox co-factor UNC-62 Homothorax/Meis targets in day 4 of adulthood (Young Adults) show significant overlap with age-regulated transcripts [10], [18]. Only factor-specific binding sites bound by less than 10 out of 57 transcription factors profiled by the modENCODE consortium were utilized. Enrichment p-value was determined by Fisher's Exact test. (C) Schematic of the UNC-62:GFP fosmid used to generate an UNC-62 fluorescent reporter. A GFP tag was inserted at the C-terminus of UNC-62 in a fosmid containing all unc-62 exons and introns, as well as ∼18.5 kb of 5′ promoter sequence. (D) The UNC-62:GFP fosmid-based transgene can rescue the embryonic lethality defects of both an unc-62 mutation (s472; denoted −) as well as a weaker mutation in unc-62 exon 7b (e644, denoted 7b(−)) [13]. 7b(+) refers to a transgene that expresses only the unc-62 exon 7b isoform. Circles indicate the number of viable progeny observed from 5 unmated hermaphrodites of each genotype, with the mean indicated by a horizontal line. (E) In hermaphrodites, UNC-62:GFP is expressed in intestine (int), neurons (neu), ventral nerve cord (vnc), vulval precursor cells (not shown), and (right) hypodermis (hyp). UNC-62 intestinal expression is stage-specific: intestine expression in L2 and earlier stages is weak or not visible (top), whereas intestinal expression is dramatically induced by the L4 stage (bottom).

Mentions: One transcription factor with known roles during embryonic and larval development, unc-62, has been shown to modulate lifespan [17] but was not previously linked to changes that occur during the normal aging process. UNC-62 is the C. elegans ortholog of Drosophila Homothorax and mammalian Meis, which are co-factors for HOX transcriptional regulators [22]. During development, knockdown of unc-62 activity yields phenotypes in maturation of the vulva, hypodermis, and the nervous system [13], [14], [15], [16]. However, during adulthood, reduction of unc-62 activity by RNAi extends lifespan by ∼30–40% (Figure 1A) [17]. Using the 1272 UNC-62 binding sites identified by the modENCODE consortium in day 4 young adult worms, we identified 399 factor-specific binding sites associated with 310 target genes. This set of direct targets includes 52 genes that show altered expression with age (2.9-fold enriched, p<10−15)(Figure 1B). In this work we characterize a new role for unc-62 in adults in order to explore the connection between an essential developmental regulator and aging.


Roles of the developmental regulator unc-62/Homothorax in limiting longevity in Caenorhabditis elegans.

Van Nostrand EL, Sánchez-Blanco A, Wu B, Nguyen A, Kim SK - PLoS Genet. (2013)

UNC-62 binds age-regulated genes and modulates lifespan.(A) Adult-specific knockdown of unc-62 extends lifespan by 30%. Approximately 150 day 1 adult wild-type (N2) worms were placed on bacteria expressing dsRNA targeting either unc-62, or control bacterial containing an empty vector. The x-axis indicates days of adulthood, and the y-axis indicates the percent of worms that remain alive at that age. The lifespan assay was performed five times (p<10−5 for each assay; one representative lifespan assay is shown). See Table S2 for lifespan data. (B) Hox co-factor UNC-62 Homothorax/Meis targets in day 4 of adulthood (Young Adults) show significant overlap with age-regulated transcripts [10], [18]. Only factor-specific binding sites bound by less than 10 out of 57 transcription factors profiled by the modENCODE consortium were utilized. Enrichment p-value was determined by Fisher's Exact test. (C) Schematic of the UNC-62:GFP fosmid used to generate an UNC-62 fluorescent reporter. A GFP tag was inserted at the C-terminus of UNC-62 in a fosmid containing all unc-62 exons and introns, as well as ∼18.5 kb of 5′ promoter sequence. (D) The UNC-62:GFP fosmid-based transgene can rescue the embryonic lethality defects of both an unc-62  mutation (s472; denoted −) as well as a weaker mutation in unc-62 exon 7b (e644, denoted 7b(−)) [13]. 7b(+) refers to a transgene that expresses only the unc-62 exon 7b isoform. Circles indicate the number of viable progeny observed from 5 unmated hermaphrodites of each genotype, with the mean indicated by a horizontal line. (E) In hermaphrodites, UNC-62:GFP is expressed in intestine (int), neurons (neu), ventral nerve cord (vnc), vulval precursor cells (not shown), and (right) hypodermis (hyp). UNC-62 intestinal expression is stage-specific: intestine expression in L2 and earlier stages is weak or not visible (top), whereas intestinal expression is dramatically induced by the L4 stage (bottom).
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Related In: Results  -  Collection

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pgen-1003325-g001: UNC-62 binds age-regulated genes and modulates lifespan.(A) Adult-specific knockdown of unc-62 extends lifespan by 30%. Approximately 150 day 1 adult wild-type (N2) worms were placed on bacteria expressing dsRNA targeting either unc-62, or control bacterial containing an empty vector. The x-axis indicates days of adulthood, and the y-axis indicates the percent of worms that remain alive at that age. The lifespan assay was performed five times (p<10−5 for each assay; one representative lifespan assay is shown). See Table S2 for lifespan data. (B) Hox co-factor UNC-62 Homothorax/Meis targets in day 4 of adulthood (Young Adults) show significant overlap with age-regulated transcripts [10], [18]. Only factor-specific binding sites bound by less than 10 out of 57 transcription factors profiled by the modENCODE consortium were utilized. Enrichment p-value was determined by Fisher's Exact test. (C) Schematic of the UNC-62:GFP fosmid used to generate an UNC-62 fluorescent reporter. A GFP tag was inserted at the C-terminus of UNC-62 in a fosmid containing all unc-62 exons and introns, as well as ∼18.5 kb of 5′ promoter sequence. (D) The UNC-62:GFP fosmid-based transgene can rescue the embryonic lethality defects of both an unc-62 mutation (s472; denoted −) as well as a weaker mutation in unc-62 exon 7b (e644, denoted 7b(−)) [13]. 7b(+) refers to a transgene that expresses only the unc-62 exon 7b isoform. Circles indicate the number of viable progeny observed from 5 unmated hermaphrodites of each genotype, with the mean indicated by a horizontal line. (E) In hermaphrodites, UNC-62:GFP is expressed in intestine (int), neurons (neu), ventral nerve cord (vnc), vulval precursor cells (not shown), and (right) hypodermis (hyp). UNC-62 intestinal expression is stage-specific: intestine expression in L2 and earlier stages is weak or not visible (top), whereas intestinal expression is dramatically induced by the L4 stage (bottom).
Mentions: One transcription factor with known roles during embryonic and larval development, unc-62, has been shown to modulate lifespan [17] but was not previously linked to changes that occur during the normal aging process. UNC-62 is the C. elegans ortholog of Drosophila Homothorax and mammalian Meis, which are co-factors for HOX transcriptional regulators [22]. During development, knockdown of unc-62 activity yields phenotypes in maturation of the vulva, hypodermis, and the nervous system [13], [14], [15], [16]. However, during adulthood, reduction of unc-62 activity by RNAi extends lifespan by ∼30–40% (Figure 1A) [17]. Using the 1272 UNC-62 binding sites identified by the modENCODE consortium in day 4 young adult worms, we identified 399 factor-specific binding sites associated with 310 target genes. This set of direct targets includes 52 genes that show altered expression with age (2.9-fold enriched, p<10−15)(Figure 1B). In this work we characterize a new role for unc-62 in adults in order to explore the connection between an essential developmental regulator and aging.

Bottom Line: Through analysis of the downstream consequences of unc-62 knockdown, we identify multiple effects linked to aging.Second, unc-62 RNAi results in a broad increase in expression of intestinal genes that typically decrease expression with age, suggesting that unc-62 activity balances intestinal resource allocation between yolk protein expression and fertility on the one hand and somatic functions on the other.These results illustrate how unc-62 regulation of intestinal gene expression is responsible for limiting lifespan during the normal aging process.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Stanford University Medical Center, Stanford, California, USA.

ABSTRACT
The normal aging process is associated with stereotyped changes in gene expression, but the regulators responsible for these age-dependent changes are poorly understood. Using a novel genomics approach, we identified HOX co-factor unc-62 (Homothorax) as a developmental regulator that binds proximal to age-regulated genes and modulates lifespan. Although unc-62 is expressed in diverse tissues, its functions in the intestine play a particularly important role in modulating lifespan, as intestine-specific knockdown of unc-62 by RNAi increases lifespan. An alternatively-spliced, tissue-specific isoform of unc-62 is expressed exclusively in the intestine and declines with age. Through analysis of the downstream consequences of unc-62 knockdown, we identify multiple effects linked to aging. First, unc-62 RNAi decreases the expression of yolk proteins (vitellogenins) that aggregate in the body cavity in old age. Second, unc-62 RNAi results in a broad increase in expression of intestinal genes that typically decrease expression with age, suggesting that unc-62 activity balances intestinal resource allocation between yolk protein expression and fertility on the one hand and somatic functions on the other. Finally, in old age, the intestine shows increased expression of several aberrant genes; these UNC-62 targets are expressed predominantly in neuronal cells in developing animals, but surprisingly show increased expression in the intestine of old animals. Intestinal expression of some of these genes during aging is detrimental for longevity; notably, increased expression of insulin ins-7 limits lifespan by repressing activity of insulin pathway response factor DAF-16/FOXO in aged animals. These results illustrate how unc-62 regulation of intestinal gene expression is responsible for limiting lifespan during the normal aging process.

Show MeSH
Related in: MedlinePlus