Exogenous and endogenous AQP12-related channels are targeted to the YPM of yolked oocytes and embryos and membrane of pancreatic ZGs. (A) Representative immunostaining of X. laevis oocytes expressing the salmon louse L. salmonis Aqp12L2 or PripL (LsAqp12L2 and LsPripL, respectively), HA-tagged human AQP12 or AQP1 (HsAQP12-HA and HsAQP1-HA, respectively), or HA-tagged zebrafish Aqp12 or Aqp1aa (DrAqp12-HA and DrAqp1aa-HA, respectively), using LsAqp12L2-or LsPripL-specific antibodies or an α-HA antibody. The plasma membrane of oocytes is indicated by an arrowhead, whereas the YPM is indicated by arrows. Uninjected oocytes were probed with each of the antibodies as indicated. Scale bars, 20 µm (insets, 10 µm). (B) Immunoelectron microscopy micrographs of a YP from a X. laevis–uninjected oocyte and an oocyte expressing the HsAQP12 showing immunogold channel particles in the YPM. C, crystalline core of yolk proteins; SL, superficial layer. Scale bars, 100 nm. (C) Stereomicroscopic image of an adult salmon louse female. Unmodified image taken from Catalán-García et al. (2021). (D) Immunostaining of LsAqp12L2 (red) in the ovary. The nuclei were counterstained with DAPI (blue), and the YPM is indicated by arrowheads. Control sections were incubated with the preabsorbed antisera. Scale bars, 50 µm (inset, 20 µm). (E) Schematic diagram of the localization and structure of the adult zebrafish pancreas. ExP, exocrine pancreas; EdP endocrine pancreas. (F) Histological section across the exocrine and endocrine pancreatic tissue (left panel), and detail of the acinar cells showing the ZGs (right panel). Scale bars, 50 and 10 µm, respectively. (G) Upper panels: Double immunostaining of the pancreatic acinar cells using a custom-made zebrafish Aqp12-specific antibody (Table S1) and the α-AMY antibody (red and green color, respectively) showing the immunolocalization of the channel in the membrane of the ZGs (arrowheads). Lower panels: Control sections incubated with the preabsorbed antiserum were negative. In both sections, nuclei were counterstained with DAPI (blue). Scale bars, 10 µm. (H) Histological section of a zebrafish vitellogenic ovarian follicle stained with hematoxylin and eosin (left), and high-magnification image of the oocyte YPs (right). Scale bars, 100 and 25 µm, respectively. (I) Immunolocalization of endogenous Aqp12 in isolated YPs from zebrafish oocytes using the α-Aqp12 antibody (green). Scale bar, 10 µm. (J and K) Stereomicroscopic image of a 24-hpf zebrafish embryo (J) and a X. laevis postvitellogenic oocyte (K), and immunostaining of endogenous AQP12 channels in the corresponding isolated YPs using the zebrafish Aqp12-specific antiserum or a commercial antibody for human AQP12, respectively. In I, J, and K, the YPs were counterstained with the α-Lv antibody (blue) and WGA (red). BF, bright field; YS, yolk sac. Scale bars, 100 µm (K, left) and 5 µm (I, J, right; and K, right). (L) Immunoblot of zebrafish ovarian follicles and 24-hpf embryos and frog oocytes probed with the same antibodies. In each panel, the blots on the right (+) were incubated with the preabsorbed Aqp12 antiserum. The arrows indicate the aquaporin monomers, and molecular mass markers (kDa) are on the left. Source data are available for this figure: SourceData FS2.