Developmental gene expression and tissue distribution of the CHIP28 water-channel protein.

Abstract

The CHIP28 water channel is a maijor component of red cell and renal tubule membranes; however, its ontogeny and tissue distribution remain undefined. Three patterns of expression were identified when CHIP28 mRNA was surveyed by in situ hybridization histochemistry in rats between embryonic day 14 and maturity. (i) CHIP28 mRNA and protein were very abundant in hematopoietic tissue and kidneys of mature rats, but strong expression did not occur until after birth, when it appeared in renal proximal tubules and descending thin limbs, red pulp of the spleen, and membranes of circulating red cells. (ii) CHIP28 mRNA was abundant in choroid plexus epithelium throughout fetal development and maturity. (iii) CHIP28 mRNA was transiently observed in periosteum, heart, vascular endothelium, and cornea during fetal development. The ontogeny of kidney and red cell CHIP28 expression coincides with the ability of kidneys to concentrate urine, suggesting that CHIP28 promotes water reabsorption in the proximal nephron and provides red cell osmoregulation needed for passage through the hypertonic medulla. Its presence in the choroid plexus suggests that CHIP28-mediated water transport contributes to secretion of cerebrospinal fluid. The functional role of CHIP28 in developing bone, heart, and eye is unclear. These findings further establish the general physiologic role of CHIP28 as a water channel involved in reabsorption, osmoregulation, and secretion. The studies also suggest other possible functions during fetal development and predict that complex mechanisms will be needed for regulation of CHIP28 gene expression in diverse tissues at distinct points in development.

Aquaporins—new players in cancer biology

“…AQP1 is expressed in vascular endothelial cells throughout the body, except in the normal central nervous system [15]. The function of AQP1 in vascular endothelial cells was established using an in vivo tumor angiogenesis assay in which wild-type and AQP1-null mice were subcutaneously implanted with B16F10 melanoma cells [14].…”

A water channel closely related to rat brain aquaporin 4 is expressed in acid‐ and pepsinogen‐secretory cells of human stomach

“…Expression patterns of aquaporins in organs or tissues are quite different from one another; AQPI is expressed in a wide variety of organs and tissues including kidney, eye, spleen, lung, and choroid plexus [13][14][15][16][17], AQP2 exclusively in the renal collecting duct [18,19], AQP3 in the kidney, colon, and *Corresponding author. Fax: (81) (3) 5802-3302.…”

“…However, there has been little information in this respect. Although AQP1 is known to be expressed in various tissues and organs [13][14][15][16][17], it has not been detected in stomach [20,21].…”

Altered ubiquitination and stability of aquaporin-1 in hypertonic stress

“…Age-and tissue-specific patterns of AQP1 expression have been shown for kidney, lung, brain, and eye (2,3). Corticosteroids induce AQP1 in rat lung in vivo (3) and an erythroleukemia cell line in vitro (4); the AQP1 proximal promoter contains classical glucorticoid response elements to which activity has been localized.…”