摘要：

p pBackground/p pP-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./p pResults/p pWe have systematically investigated expression and developmental function of the six, ittat-1 /itthrough it6/it, subfamily IV P-type ATPase genes encoded in the itCaenorhabditis elegans /itgenome. ittat-5 /itis the only ubiquitously-expressed essential gene in the group. ittat-6 /itis a poorly-transcribed recent duplicate of ittat-5/it. ittat-2 /itthrough it4 /itexhibit tissue-specific developmentally-regulated expression patterns. Strong expression of both ittat-2 /itand ittat-4 /itoccurs 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. ittat-2 /italone is expressed in the pharyngeal gland cells, the excretory system and a few cells of the developing vulva. The expression pattern of ittat-3 /itis almost completely different from those of ittat-2 /itand ittat-4/it. ittat-3 /itexpression 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 ittat-1 /itthrough it4 /itindividually interferes little or not at all with the regular progression of organism growth and development under normal conditions. However, ittat-2 /itthrough it4 /itbecome essential for reproductive growth during sterol starvation./p pConclusion/p pittat-5 /itlikely encodes a housekeeping protein that performs the proposed aminophospholipid translocase function routinely. Although individually dispensable, ittat-1 /itthrough it4 /itseem to be at most only partly redundant. Expression patterns and the sterol deprivation hypersensitivity deletion phenotype of ittat-2 /itthrough it4 /itsuggest 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./p

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