Category Archives: Isoforms

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(9)

DISCUSSION(9) In summary, the expression of various isoforms of the same V-ATPase subunit in narrow and clear cells strongly indicates that these cells are fully equipped for active proton secretion and that they possess potentially important backup mechanisms that may compensate for the lack of one or more V-ATPase subunit isoforms. This underlies the important role that the V-ATPase plays in acidifying the lumen of the epididymis, a process that is important for sperm maturation and storage. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(8)

Some isoforms could serve as a possible alternative mechanism for the active role played by the predominant one in the V-ATPase holoenzyme. Mutations of some subunits of the V-ATPase, including Bl and a4, are linked to renal distal tubular acidosis and deafness. Our finding that a4 and Bl are highly expressed in narrow and clear cells of the epididymis raised the possibility that fertility might be altered in patients harboring these mutations. Long-term clinical follow-up of these young patients will be required to address this question. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(7)

DISCUSSION(7) Alternatively, various subunits of the V-ATPase, including subunits a, d, A, and C, have been shown to control the activity of the V-ATPase by modulating the coupling of proton transport to ATP hydrolysis. The presence of various isoforms of subunits a, d, and C in clear cells may, therefore, reflect different levels of V-ATPase activity in the membrane domains and intracellular compartments in which they are expressed. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(6)

A similar function has been previously suggested for the 56-kDa subunit (B1), which was detected in nonacidifying endosomes isolated from kidney collecting duct principal cells. Alternatively, some unidentified V0 domain subunit isoforms may be expressed in principal cells and may serve to anchor dl in their apical membrane. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(5)

DISCUSSION(5) These results are in agreement with the notion that TGN-derived vesicles are acidic and that the V-ATPase plays an active role in this process. Vesicle acidification induces the recruitment of coat proteins and small GTPases of the ADP-ribosylation factor (ARF) family, a process that is important for the appropriate targeting and recycling of various membrane proteins, including GLUT4 and AQP2. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(4)

Because of its brighter apical staining in clear cells and its high expression in kidney intercalated cells, d2 appears to be the predominant isoform in proton-secreting narrow and clear cells. Principal Cell Localization Interestingly, subunit A was detected in principal cells, where it was localized in intracellular structures closely associated with but not identical to the TGN38-labeled trans-Golgi network (TGN). (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(3)

DISCUSSION(3) The presence of G2 in the epididymis was not investigated here because this subunit has been previously shown to be specific for the brain and absent from the kidney. In addition to their localization in the apical plasma membrane and subapical vesicles, a faint cytosolic staining was also observed for A, C1, C2, G1, and G3, similarly to the previously reported localization of other subunits of the V1 domain, including subunit E2, in the soluble fraction of clear cells. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(2)

The precise colocalization of subunit A with subunit E2 in apical microvilli and subapical vesicles is consistent with the assembly of these unique subunit isoforms to form the V-ATPase complex. This result indicates that clear cells use the A subunit for net luminal proton secretion in the epididymis. Both the ubiquitous isoform C1 and the more restricted C2 isoform were expressed in clear cells. Two C2 isoforms, C2a and C2b, resulting from alternative mRNA splicing, have been identified. C2a was detected in the lung and C2b in the kidney. (more…)

Distinct Expression Patterns of Different Subunit Isoforms: DISCUSSION(1)

DISCUSSION(1) Immunofluorescence was used to examine the expression and the cellular and subcellular localization of five subunits of the V-ATPase and some of their respective isoforms in rat epididymis and vas deferens: A, C1, C2, G1, G3, a1, a2, a4, d1, and d2. All five subunits were detected in epithelial cells of these organs but showed specific patterns of expression (Fig. 10). (more…)

Distinct Expression Patterns of Different Subunit Isoforms: RESULTS(5)

Localization of the d Subunit of the V-ATPase: d1 and d2 Isoforms The d1 isoform was detected in the apical pole of narrow cells (data not shown) and of clear cells in the epididymis (arrows in Fig. 9A) and vas deferens (data not shown), where it colocalizes with the E2 subunit (arrows in Fig. 9, C and E). The staining for d1 in clear cells was weaker compared to other subunits and did not allow for the exact localization of this subunit in apical microvilli and/or subapical endosomes. Immunogold electron microscopy will be required to determine with precision the subcellular localization of this subunit in clear cells. (more…)