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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 knockdown extends lifespan in intestinal and hypodermal tissues.(A) Tissue-specific RNAi is achieved in worms by starting with a strain deficient for the RNAi pathway due to the rde-1(ne219) mutation. A transgene expressing rde-1 under a tissue-specific promoter (examples shown use elt-2 to drive intestine-specific expression, or hlh-1 to drive muscle-specific expression) rescues the RNAi pathway only in the desired tissue. (B) unc-62 RNAi extends lifespan by ∼30% (p<10−5) in wild-type worms. (C–D) A ∼30% extension is observed when unc-62 is knocked down in (C) a strain expressing rde-1 from the elt-2 intestinal promoter (strain OLB11) or (D) the lin-26 hypodermal promoter (strain NR222). (E–G) In contrast, unc-62 knockdown in (E) neurons and vulval precursor cells (a short unc-62 promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK742), (F) muscle (hlh-1 promoter; strain NR350), or (G) uterine cells (fos-1A promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK640) did not significantly extend lifespan (p>0.01). The rrf-3(pk1426) mutation provides increased RNAi sensitivity in neuronal cells. Except for uterine-specific RNAi, lifespans were performed two or more times (Table S2). Lifespan data shown is aggregated from multiple simultaneous experiments.
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pgen-1003325-g003: UNC-62 knockdown extends lifespan in intestinal and hypodermal tissues.(A) Tissue-specific RNAi is achieved in worms by starting with a strain deficient for the RNAi pathway due to the rde-1(ne219) mutation. A transgene expressing rde-1 under a tissue-specific promoter (examples shown use elt-2 to drive intestine-specific expression, or hlh-1 to drive muscle-specific expression) rescues the RNAi pathway only in the desired tissue. (B) unc-62 RNAi extends lifespan by ∼30% (p<10−5) in wild-type worms. (C–D) A ∼30% extension is observed when unc-62 is knocked down in (C) a strain expressing rde-1 from the elt-2 intestinal promoter (strain OLB11) or (D) the lin-26 hypodermal promoter (strain NR222). (E–G) In contrast, unc-62 knockdown in (E) neurons and vulval precursor cells (a short unc-62 promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK742), (F) muscle (hlh-1 promoter; strain NR350), or (G) uterine cells (fos-1A promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK640) did not significantly extend lifespan (p>0.01). The rrf-3(pk1426) mutation provides increased RNAi sensitivity in neuronal cells. Except for uterine-specific RNAi, lifespans were performed two or more times (Table S2). Lifespan data shown is aggregated from multiple simultaneous experiments.

Mentions: As unc-62 is expressed in a variety of tissues, we wanted to identify the tissues in which unc-62 functions to affect lifespan of the entire organism. To do this, we performed RNAi knockdown of unc-62 in strains that generate an RNAi response only in specific tissues. These strains contain a mutation in the RNAi pathway (rde-1) that leads to inactivation of the RNAi response, as well as a transgene expressing rde-1 under a tissue-specific promoter to restore the RNAi response only in that tissue (Figure 3A) [24], [25]. We found that knockdown of unc-62 either only in intestine or only in the hypodermis was sufficient to cause a ∼30% extension of median lifespan (Figure 3C–3D). As a control, we crossed in the unc-62:GFP transgene and observed that GFP RNAi reduced GFP expression only in the proper tissue for the intestinal- and the hypodermal-specific RNAi strains (Figure S3). However, unc-62 RNAi did not have a significant effect on longevity in muscle tissue, neuronal tissue or the uterus (Figure 3E–3G). These results indicate that wild-type unc-62 activity in the intestine and hypodermis is critical for its role in limiting wild-type lifespan. In this work, we primarily focus on intestinal activity of unc-62 and the intestine-specific unc-62(7a) isoform.


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 knockdown extends lifespan in intestinal and hypodermal tissues.(A) Tissue-specific RNAi is achieved in worms by starting with a strain deficient for the RNAi pathway due to the rde-1(ne219) mutation. A transgene expressing rde-1 under a tissue-specific promoter (examples shown use elt-2 to drive intestine-specific expression, or hlh-1 to drive muscle-specific expression) rescues the RNAi pathway only in the desired tissue. (B) unc-62 RNAi extends lifespan by ∼30% (p<10−5) in wild-type worms. (C–D) A ∼30% extension is observed when unc-62 is knocked down in (C) a strain expressing rde-1 from the elt-2 intestinal promoter (strain OLB11) or (D) the lin-26 hypodermal promoter (strain NR222). (E–G) In contrast, unc-62 knockdown in (E) neurons and vulval precursor cells (a short unc-62 promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK742), (F) muscle (hlh-1 promoter; strain NR350), or (G) uterine cells (fos-1A promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK640) did not significantly extend lifespan (p>0.01). The rrf-3(pk1426) mutation provides increased RNAi sensitivity in neuronal cells. Except for uterine-specific RNAi, lifespans were performed two or more times (Table S2). Lifespan data shown is aggregated from multiple simultaneous experiments.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3585033&req=5

pgen-1003325-g003: UNC-62 knockdown extends lifespan in intestinal and hypodermal tissues.(A) Tissue-specific RNAi is achieved in worms by starting with a strain deficient for the RNAi pathway due to the rde-1(ne219) mutation. A transgene expressing rde-1 under a tissue-specific promoter (examples shown use elt-2 to drive intestine-specific expression, or hlh-1 to drive muscle-specific expression) rescues the RNAi pathway only in the desired tissue. (B) unc-62 RNAi extends lifespan by ∼30% (p<10−5) in wild-type worms. (C–D) A ∼30% extension is observed when unc-62 is knocked down in (C) a strain expressing rde-1 from the elt-2 intestinal promoter (strain OLB11) or (D) the lin-26 hypodermal promoter (strain NR222). (E–G) In contrast, unc-62 knockdown in (E) neurons and vulval precursor cells (a short unc-62 promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK742), (F) muscle (hlh-1 promoter; strain NR350), or (G) uterine cells (fos-1A promoter in an rde-1(ne219);rrf-3(pk1426) background; strain NK640) did not significantly extend lifespan (p>0.01). The rrf-3(pk1426) mutation provides increased RNAi sensitivity in neuronal cells. Except for uterine-specific RNAi, lifespans were performed two or more times (Table S2). Lifespan data shown is aggregated from multiple simultaneous experiments.
Mentions: As unc-62 is expressed in a variety of tissues, we wanted to identify the tissues in which unc-62 functions to affect lifespan of the entire organism. To do this, we performed RNAi knockdown of unc-62 in strains that generate an RNAi response only in specific tissues. These strains contain a mutation in the RNAi pathway (rde-1) that leads to inactivation of the RNAi response, as well as a transgene expressing rde-1 under a tissue-specific promoter to restore the RNAi response only in that tissue (Figure 3A) [24], [25]. We found that knockdown of unc-62 either only in intestine or only in the hypodermis was sufficient to cause a ∼30% extension of median lifespan (Figure 3C–3D). As a control, we crossed in the unc-62:GFP transgene and observed that GFP RNAi reduced GFP expression only in the proper tissue for the intestinal- and the hypodermal-specific RNAi strains (Figure S3). However, unc-62 RNAi did not have a significant effect on longevity in muscle tissue, neuronal tissue or the uterus (Figure 3E–3G). These results indicate that wild-type unc-62 activity in the intestine and hypodermis is critical for its role in limiting wild-type lifespan. In this work, we primarily focus on intestinal activity of unc-62 and the intestine-specific unc-62(7a) isoform.

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