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An unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the C. elegans putative aminophospholipid translocases.

Lyssenko NN, Miteva Y, Gilroy S, Hanna-Rose W, Schlegel RA - BMC Dev. Biol. (2008)

Bottom Line: Strong expression of both tat-2 and tat-4 occurs in the intestine and certain other cells of the alimentary system.Although individually dispensable, tat-1 through 4 seem to be at most only partly redundant.These findings uncover an unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the genes encoding the putative aminophospholipid translocases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. lyssenn@ccf.org

ABSTRACT

Background: P-type ATPases in subfamily IV are exclusively eukaryotic transmembrane proteins that have been proposed to directly translocate the aminophospholipids phosphatidylserine and phosphatidylethanolamine from the exofacial to the cytofacial monolayer of the plasma membrane. Eukaryotic genomes contain many genes encoding members of this subfamily. At present it is unclear why there are so many genes of this kind per organism or what individual roles these genes perform in organism development.

Results: We have systematically investigated expression and developmental function of the six, tat-1 through 6, subfamily IV P-type ATPase genes encoded in the Caenorhabditis elegans genome. tat-5 is the only ubiquitously-expressed essential gene in the group. tat-6 is a poorly-transcribed recent duplicate of tat-5. tat-2 through 4 exhibit tissue-specific developmentally-regulated expression patterns. Strong expression of both tat-2 and tat-4 occurs in the intestine and certain other cells of the alimentary system. The two are also expressed in the uterus, during spermatogenesis and in the fully-formed spermatheca. tat-2 alone is expressed in the pharyngeal gland cells, the excretory system and a few cells of the developing vulva. The expression pattern of tat-3 is almost completely different from those of tat-2 and tat-4. tat-3 expression is detectable in the steroidogenic tissues: the hypodermis and the XXX cells, as well as in most cells of the pharynx (except gland), various tissues of the reproductive system (except uterus and spermatheca) and seam cells. Deletion of tat-1 through 4 individually interferes little or not at all with the regular progression of organism growth and development under normal conditions. However, tat-2 through 4 become essential for reproductive growth during sterol starvation.

Conclusion: tat-5 likely encodes a housekeeping protein that performs the proposed aminophospholipid translocase function routinely. Although individually dispensable, tat-1 through 4 seem to be at most only partly redundant. Expression patterns and the sterol deprivation hypersensitivity deletion phenotype of tat-2 through 4 suggest that these genes carry out subtle metabolic functions, such as fine-tuning sterol metabolism in digestive or steroidogenic tissues. These findings uncover an unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the genes encoding the putative aminophospholipid translocases.

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Detected transcripts of tat-1 through 4. While tat-1 (A) and tat-2 (B) consist of generally shorter exons and undergo significant alternative splicing, tat-3 (C) and tat-4 (D) include somewhat longer exons and encode essentially only one version of the product.
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Figure 1: Detected transcripts of tat-1 through 4. While tat-1 (A) and tat-2 (B) consist of generally shorter exons and undergo significant alternative splicing, tat-3 (C) and tat-4 (D) include somewhat longer exons and encode essentially only one version of the product.

Mentions: The C. elegans genome encodes six predicted members of the P-type ATPase subfamily IV. The genes are named transbilayer amphipath transporter (tat) 1 through 6 (Additional file 1). The four detected splice isoforms of tat-1 differ with respect to the final five exons (Figure 1A). Each isoform has a distinct stop codon and is predicted to generate a product with a divergent C terminus (Additional file 2). The five detected splice isoforms of tat-2 differ with respect to the first two and the penultimate exons and are predicted to generate four products with some sequence variability at the very N and C termini (Figure 1B). Only two slightly different isoforms of tat-3 were identified (Figure 1C). The product of the longer isoform contains a few extra C-terminal amino acids, which are absent in the shorter version. The tat-4 locus includes two open reading frames (ORFs), tat-4 and T24H7.6, which appear to form an operon (Figure 1D). T24H7.6, but not tat-4, cDNA could be amplified using a splice leader 2 (SL2) primer. In C. elegans, trans-splicing to SL2 usually indicates that a gene occupies a subordinate position in an operon [19]. The tat-4 stop codon resides in the same exon as at least three weak polyadenylation signals (Additional file 2). Bicistronic tat-4 and T24H7.6 messages were detected that terminate with the sole T24H7.6 polyadenilation signal and likely arise when the three tat-4 polyadenylation signals fail to induce poly(A) tail addition. The choice of polyadenylation site affects translation of neither tat-4 nor T24H7.6.


An unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the C. elegans putative aminophospholipid translocases.

Lyssenko NN, Miteva Y, Gilroy S, Hanna-Rose W, Schlegel RA - BMC Dev. Biol. (2008)

Detected transcripts of tat-1 through 4. While tat-1 (A) and tat-2 (B) consist of generally shorter exons and undergo significant alternative splicing, tat-3 (C) and tat-4 (D) include somewhat longer exons and encode essentially only one version of the product.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2572054&req=5

Figure 1: Detected transcripts of tat-1 through 4. While tat-1 (A) and tat-2 (B) consist of generally shorter exons and undergo significant alternative splicing, tat-3 (C) and tat-4 (D) include somewhat longer exons and encode essentially only one version of the product.
Mentions: The C. elegans genome encodes six predicted members of the P-type ATPase subfamily IV. The genes are named transbilayer amphipath transporter (tat) 1 through 6 (Additional file 1). The four detected splice isoforms of tat-1 differ with respect to the final five exons (Figure 1A). Each isoform has a distinct stop codon and is predicted to generate a product with a divergent C terminus (Additional file 2). The five detected splice isoforms of tat-2 differ with respect to the first two and the penultimate exons and are predicted to generate four products with some sequence variability at the very N and C termini (Figure 1B). Only two slightly different isoforms of tat-3 were identified (Figure 1C). The product of the longer isoform contains a few extra C-terminal amino acids, which are absent in the shorter version. The tat-4 locus includes two open reading frames (ORFs), tat-4 and T24H7.6, which appear to form an operon (Figure 1D). T24H7.6, but not tat-4, cDNA could be amplified using a splice leader 2 (SL2) primer. In C. elegans, trans-splicing to SL2 usually indicates that a gene occupies a subordinate position in an operon [19]. The tat-4 stop codon resides in the same exon as at least three weak polyadenylation signals (Additional file 2). Bicistronic tat-4 and T24H7.6 messages were detected that terminate with the sole T24H7.6 polyadenilation signal and likely arise when the three tat-4 polyadenylation signals fail to induce poly(A) tail addition. The choice of polyadenylation site affects translation of neither tat-4 nor T24H7.6.

Bottom Line: Strong expression of both tat-2 and tat-4 occurs in the intestine and certain other cells of the alimentary system.Although individually dispensable, tat-1 through 4 seem to be at most only partly redundant.These findings uncover an unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the genes encoding the putative aminophospholipid translocases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. lyssenn@ccf.org

ABSTRACT

Background: P-type ATPases in subfamily IV are exclusively eukaryotic transmembrane proteins that have been proposed to directly translocate the aminophospholipids phosphatidylserine and phosphatidylethanolamine from the exofacial to the cytofacial monolayer of the plasma membrane. Eukaryotic genomes contain many genes encoding members of this subfamily. At present it is unclear why there are so many genes of this kind per organism or what individual roles these genes perform in organism development.

Results: We have systematically investigated expression and developmental function of the six, tat-1 through 6, subfamily IV P-type ATPase genes encoded in the Caenorhabditis elegans genome. tat-5 is the only ubiquitously-expressed essential gene in the group. tat-6 is a poorly-transcribed recent duplicate of tat-5. tat-2 through 4 exhibit tissue-specific developmentally-regulated expression patterns. Strong expression of both tat-2 and tat-4 occurs in the intestine and certain other cells of the alimentary system. The two are also expressed in the uterus, during spermatogenesis and in the fully-formed spermatheca. tat-2 alone is expressed in the pharyngeal gland cells, the excretory system and a few cells of the developing vulva. The expression pattern of tat-3 is almost completely different from those of tat-2 and tat-4. tat-3 expression is detectable in the steroidogenic tissues: the hypodermis and the XXX cells, as well as in most cells of the pharynx (except gland), various tissues of the reproductive system (except uterus and spermatheca) and seam cells. Deletion of tat-1 through 4 individually interferes little or not at all with the regular progression of organism growth and development under normal conditions. However, tat-2 through 4 become essential for reproductive growth during sterol starvation.

Conclusion: tat-5 likely encodes a housekeeping protein that performs the proposed aminophospholipid translocase function routinely. Although individually dispensable, tat-1 through 4 seem to be at most only partly redundant. Expression patterns and the sterol deprivation hypersensitivity deletion phenotype of tat-2 through 4 suggest that these genes carry out subtle metabolic functions, such as fine-tuning sterol metabolism in digestive or steroidogenic tissues. These findings uncover an unexpectedly high degree of specialization and a widespread involvement in sterol metabolism among the genes encoding the putative aminophospholipid translocases.

Show MeSH
Related in: MedlinePlus