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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.

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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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Higher sensitivity to sterol limitation of tat-4(tm1801); tat-3(tm1275) double mutants in comparison with tat-4(tm1801) single mutants. The dark lines on the photographs are numbers written on the underside of plates.
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Figure 9: Higher sensitivity to sterol limitation of tat-4(tm1801); tat-3(tm1275) double mutants in comparison with tat-4(tm1801) single mutants. The dark lines on the photographs are numbers written on the underside of plates.

Mentions: The above data suggest that tat-3 is not a major player in sterol metabolism; however, the gene is expressed in the hypodermis, a major steroidogenic tissue [28], and in the pharynx, a potential sterol storage organ [32]. To test whether tat-3 contributes marginally to sterol metabolism, tat-3(tm1275) mutants were crossed with tat-4(tm1801) mutants to derive a double mutant of the two genes. tat-3 and tat-4 expression patterns overlap only in the pharyngeal-intestinal valve (Table 1), and in terms of development and reproduction under regular conditions, tat-4(tm1801); tat-3(tm1275) animals are indistinguishable from N2 nematodes (Figure 7). On sterol-deprivation test plates, double mutants of the two genes performed worse than tat-4(tm1801) nematodes (Figure 9). tat-4(tm1801) populations were noticeably larger than tat-4(tm1801); tat-3(tm1275) populations by day 7 on 1000 ng/ml cholesterol concentration plates. By day 8 on the same plates, tat-4(tm1801) animals cleared all food, while there were still plenty of bacteria to consume for the double mutants. Growth was minimal on 100 ng/ml and lower cholesterol concentration plates for both tat-4(tm1801); tat-3(tm1275) and tat-4(tm1801) animals during the 9-day observation period. Thus, it seems deletion of tat-3 exacerbates sterol-deprivation hypersensitivity of tat-4 mutants.


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)

Higher sensitivity to sterol limitation of tat-4(tm1801); tat-3(tm1275) double mutants in comparison with tat-4(tm1801) single mutants. The dark lines on the photographs are numbers written on the underside of plates.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Higher sensitivity to sterol limitation of tat-4(tm1801); tat-3(tm1275) double mutants in comparison with tat-4(tm1801) single mutants. The dark lines on the photographs are numbers written on the underside of plates.
Mentions: The above data suggest that tat-3 is not a major player in sterol metabolism; however, the gene is expressed in the hypodermis, a major steroidogenic tissue [28], and in the pharynx, a potential sterol storage organ [32]. To test whether tat-3 contributes marginally to sterol metabolism, tat-3(tm1275) mutants were crossed with tat-4(tm1801) mutants to derive a double mutant of the two genes. tat-3 and tat-4 expression patterns overlap only in the pharyngeal-intestinal valve (Table 1), and in terms of development and reproduction under regular conditions, tat-4(tm1801); tat-3(tm1275) animals are indistinguishable from N2 nematodes (Figure 7). On sterol-deprivation test plates, double mutants of the two genes performed worse than tat-4(tm1801) nematodes (Figure 9). tat-4(tm1801) populations were noticeably larger than tat-4(tm1801); tat-3(tm1275) populations by day 7 on 1000 ng/ml cholesterol concentration plates. By day 8 on the same plates, tat-4(tm1801) animals cleared all food, while there were still plenty of bacteria to consume for the double mutants. Growth was minimal on 100 ng/ml and lower cholesterol concentration plates for both tat-4(tm1801); tat-3(tm1275) and tat-4(tm1801) animals during the 9-day observation period. Thus, it seems deletion of tat-3 exacerbates sterol-deprivation hypersensitivity of tat-4 mutants.

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