Immunohistochemical localization of calbindin-D28k during the development of the rabbit nephron

Oncomodulin: The Enigmatic Parvalbumin Protein

EF-hand Ca²⁺-binding protein family members, α- and β-parvalbumins have been studied for decades. Yet, considerable information is lacking distinguishing functional differences between mammalian α-parvalbumin (PVALB) and oncomodulin (OCM), a branded β-parvalbumin. Herein, we provide an overview detailing the current body of work centered around OCM as an EF-Hand Ca²⁺-binding protein and describe potential mechanisms of OCM function within the inner ear and immune cells. Additionally, we posit that OCM is evolutionarily distinct from PVALB and most other β-parvalbumins. This review summarizes recent studies pertaining to the function of OCM and emphasizes OCM as a parvalbumin possessing a unique cell and tissue distribution, Ca²⁺ buffering capacity and phylogenetic origin.

Isoforms of Spectrin and Ankyrin Reflect the Functional Topography of the Mouse Kidney

The kidney displays specialized regions devoted to filtration, selective reabsorption, and electrolyte and metabolite trafficking. The polarized membrane pumps, channels, and transporters responsible for these functions have been exhaustively studied. Less examined are the contributions of spectrin and its adapter ankyrin to this exquisite functional topography, despite their established contributions in other tissues to cellular organization. We have examined in the rodent kidney the expression and distribution of all spectrins and ankyrins by qPCR, Western blotting, immunofluorescent and immuno electron microscopy. Four of the seven spectrins (αΙΙ, βΙ, βΙΙ, and βΙΙΙ) are expressed in the kidney, as are two of the three ankyrins (G and B). The levels and distribution of these proteins vary widely over the nephron. αΙΙ/βΙΙ is the most abundant spectrin, found in glomerular endothelial cells; on the basolateral membrane and cytoplasmic vesicles in proximal tubule cells and in the thick ascending loop of Henle; and less so in the distal nephron. βΙΙΙ spectrin largely replaces βΙΙ spectrin in podocytes, Bowman’s capsule, and throughout the distal tubule and collecting ducts. βΙ spectrin is only marginally expressed; its low abundance hinders a reliable determination of its distribution. Ankyrin G is the most abundant ankyrin, found in capillary endothelial cells and all tubular segments. Ankyrin B populates Bowman’s capsule, podocytes, the ascending thick loop of Henle, and the distal convoluted tubule. Comparison to the distribution of renal protein 4.1 isoforms and various membrane proteins indicates a complex relationship between the spectrin scaffold, its adapters, and various membrane proteins. While some proteins (e.g. ankyrin B, βΙΙΙ spectrin, and aquaporin 2) tend to share a similar distribution, there is no simple mapping of different spectrins or ankyrins to most membrane proteins. The implications of this data are discussed.

Control of kidney development by calcium ions

From the formation of a simple kidney in amphibian larvae, the pronephros, to the formation of the more complex mammalian kidney, the metanephros, calcium is present through numerous steps of tubulogenesis and nephron induction. Several calcium-binding proteins such as regucalcin/SMP-30 and calbindin-D28k are commonly used to label pronephric tubules and metanephric ureteral epithelium, respectively. However, the involvement of calcium and calcium signalling at various stages of renal organogenesis was not clearly delineated. In recent years, several studies have pinpointed an unsuspected role of calcium in determination of the pronephric territory and for conversion of metanephric mesenchyme into nephrons. Influx of calcium and calcium transients have been recorded in the pool of renal progenitors to allow tubule formation, highlighting the occurrence of calcium-dependent signalling events during early kidney development. Characterization of nuclear calcium signalling is emerging. Implication of the non-canonical calcium/NFAT Wnt signalling pathway as an essential mechanism to promote nephrogenesis has recently been demonstrated. This review examines the current knowledge of the impact of calcium ions during embryonic development of the kidney. It focuses on Ca(2+) binding proteins and Ca(2+) sensors that are involved in renal organogenesis and briefly examines the link between calcium-dependent signals and polycystins.

Calbindin-D28k gene expression in the developing mouse kidney

Calbindin-D28k appears in the metanephric kidney during embryogenesis. We studied the temporal appearance and spatial distribution of calbindin-D28k mRNA in the developing kidneys of 12-day fetal through 21-day postnatal mice by in situ hybridization. 35S-UTP-labeled antisense (cRNA) probe to calbindin-D28k mRNA hybridized to the ureteric buds of 12-day embryos, whereas adjacent metanephrogenic tissue was unlabeled. By embryonic day 13, Y-shaped bodies of "advancing" ureteric buds were labeled intensely. In 16-day embryos, ampullae of ureteric buds were located immediately beneath the renal capsule and labeled strongly, in contrast to metanephric tubules and S-shaped bodies. The former were unlabeled and the latter were labeled only at points of contact with the ampullae. Subsequently, the ampullae of the metanephric ureteric buds hybridized with the cRNA probe, and from the 18th embryonic to the 21st postnatal day, this labeling was intense. The cRNA probe did not hybridize with the renal vesicles, proximal tubules, or tubular segments of Henle's loop derived from nephrogenic blastema, but it did label distal nephron segments. By the 21st postnatal day, collecting ducts and ureter no longer were labeled. In conclusion, calbindin-D28k mRNA is present in the developing mouse kidney, and its distribution during nephrogenesis is identical to that of calbindin-D28k per se. Collectively, these findings show that the calbindin-D28k gene is transcribed and its message is translated by the cells of the ureteric bud during the initial stage of renal morphogenesis.

Ontogeny of the distribution and colocalization of Calbindin D28K within neural and endocrine cells of the gastrointestinal tract of fetal and neonatal sheep

Using immunocytochemical techniques we have demonstrated that Calbindin D28K (CaBP) is present in the gastrointestinal tract of ovine fetuses early in development (by day 45). At day 45, CaBP was limited to neuronal elements in the developing intestine. By day 100, CaBP immunoreactivity was abundant in both epithelial endocrine cells and nerves of the submucous and myenteric ganglia. The location of CaBP containing cells and fibers was similar in duodenal sections taken from day 100 and term (145 days), as well as those taken from 24-48 h postnatal lambs. CaBP is colocalized in endocrine cells containing gastrin, glucagon, somatostatin and neurotensin, but not glucose dependent insulinotrophic peptide (GIP). Furthermore, it is extensively colocalized in nerve fibers and cells containing neurotensin but not somatostatin or vasoactive intestinal peptide. The colocalization of CaBP within various endocrine and nerve cells does not change in fetal sheep over the last one-third of gestation and there is no difference between fetal and neonatal sheep.

The expression of specific proteins in cultured renal collecting duct cells

It is still uncertain whether cell cultures attain the functional maturity of corresponding in vivo cells. The degree of differentiation of cultured collecting-duct (CD) epithelium cells was therefore examined using immunohistochemical procedures. Three monoclonal antibodies (mabs CD1, CD2, and CD3) were raised against proteins (PCD) isolated from the renal papilla. At Western-blot analysis, each of these antibodies reacted with a specific protein that was distinguishable according to its molecular weight [PCD1, 190 kilodaltons (kDa); PCD2, 210 kDa; PCD3, 50 kDa]. Using immunofluorescence, these proteins were found to be localized exclusively in the renal CD system. Other renal structures, such as the proximal or distal tubular portions, the glomeruli and the interstitial network, were not reactive. The mabs, CD2 and CD3, labeled both the cortical and medullary CD in a uniform way, whereas mab CD1 produced heterogeneous immunolabeling along the length of the cortical, medullary, and papillary CD. As revealed by immunohistochemistry, the mabs revealed differences with respect to the expression of the specific renal proteins in cultured CD cells. In polar-differentiated epithelium cultured for 5 days on a specific renal support, mab CD1 was unreactive, whereas mabs CD2 and CD3 were positive. This demonstrated the biochemical immaturity of this cultured epithelium with respect to CD1 reactivity. In morphologically dedifferentiated CD monolayer cells grown on the bottom of a culture dish, only a weak reaction for mab CD3 was observed. The loss of epithelial polarization in CD monolayer cells obviously coincides with the absence of the renal proteins PCD1 and PCD2.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of chronic vitamin D deficiency on the skeleton in the adult rabbit

Albino rabbits were fed a 1.0% Ca, 0.5% P, vitamin D-deficient diet for 11.7 to 31.3 mo. Control rabbits were fed either this diet with the addition of 2.2 units/gm of vitamin D3 or a standard laboratory rabbit ration. Serum levels of 25-OH-D and 1,25-(OH)2D were both undetectable in all vitamin D-deficient rabbits but were present at levels typically found in other species in the control rabbits. Vitamin D deficiency resulted in elevated serum PTH values but did not produce significant changes in serum Ca levels, femur length, femur ash weight to body weight ratio, or tibial breaking strength. The vitamin D-deficient rabbits could be readily separated into two distinct subgroups. Four of these rabbits were normophosphatemic (P = 3.7 +/- 0.4 mg/dl) whereas the other five were severely hypophosphatemic (P = 0.8 +/- 0.2 mg/dl). During the last 10 days of the study the control and normophosphatemic vitamin D-deficient rabbits were in positive Ca and zero P balance. The hypophosphatemic vitamin D-deficient rabbits were in zero Ca and negative P balance. This negative P balance resulted from a net intestinal secretion, as urinary P excretion was negligible. Femur ash weight as a percentage of dry weight was decreased in hypophosphatemic but not the normophosphatemic vitamin D-deficient rabbits. Histomorphometric analyses indicated the bones from the normophosphatemic vitamin D-deficient rabbits were normal. In contrast, vertebral trabecular bone from the hypophosphatemic rabbits contained large amounts of osteoid that was not mineralizing, as indicated by a failure to take up the fluorescent label calcein.(ABSTRACT TRUNCATED AT 250 WORDS)