BACKGROUND AND PURPOSE Splice variants of P2X7 receptor transcripts contribute to the diversity of receptor‐mediated responses. Here, we investigated expression and function of C‐terminal truncated (ΔC) variants of the mP2X7 receptor, which are predicted to escape inactivation in one strain of P2X7−/− mice (Pfizer KO). EXPERIMENTAL APPROACH Expression in wild‐type (WT) and Pfizer KO tissue was investigated by reverse transcription (RT)‐PCR and Western blot analysis. ΔC variants were also cloned and expressed in HEK293 cells to investigate their assembly, trafficking and function. KEY RESULTS RT‐PCR indicates expression of a ΔC splice variant in brain, salivary gland (SG) and spleen from WT and Pfizer KO mice. An additional ΔC hybrid transcript, containing sequences of P2X7 upstream of exon 12, part of exon 13 followed in‐frame by the sequence of the vector used to disrupt the P2X7 gene, was also identified in the KO mice. By blue native (BN) PAGE analysis and the use of cross linking reagents followed by SDS‐PAGE, P2X7 trimers, dimers and monomers were detected in the spleen and SG of Pfizer KO mice. The molecular mass was reduced compared with P2X7 in WT mice tissue, consistent with a ΔC variant. When expressed in HEK293 cells the ΔC variants were inefficiently trafficked to the cell surface and agonist‐evoked whole cell currents were small. Co‐expressed with P2X7A, the ΔC splice variant acted in a dominant negative fashion to inhibit function. CONCLUSIONS AND IMPLICATIONS Pfizer KO mice are not null for P2X7 receptor expression but express ΔC variants with reduced function.

SummaryCell and organelle membranes consist of a complex mixture of phospholipids (PLs) that determine their size, shape, and function. Phosphatidylcholine (PC) is the most abundant phospholipid in eukaryotic membranes, yet how cells sense and regulate its levels in vivo remains unclear. Here we show that PCYT1A, the rate-limiting enzyme of PC synthesis, is intranuclear and re-locates to the nuclear membrane in response to the need for membrane PL synthesis in yeast, fly, and mammalian cells. By aligning imaging with lipidomic analysis and data-driven modeling, we demonstrate that yeast PCYT1A membrane association correlates with membrane stored curvature elastic stress estimates. Furthermore, this process occurs inside the nucleus, although nuclear localization signal mutants can compensate for the loss of endogenous PCYT1A in yeast and in fly photoreceptors. These data suggest an ancient mechanism by which nucleoplasmic PCYT1A senses surface PL packing defects on the inner nuclear membrane to control PC homeostasis.