Cloning and characterization of murine Aqp5: evidence for a conserved aquaporin gene cluster

Aquaporin 5 (Aqp5), a member of the aquaporin family of membrane water channels, is thought to modulate the osmolality of fluids in the eye, lung, and salivary gland. Here, we report the cloning and genomic characterization of murine Aqp5 and its expression in relevant mouse tissues. This gene, comprised of four exons encoding 265 amino acids (121, 55, 28, and 61 amino acids respectively), is transcribed into an approximate 1.8-kb mRNA detected in lung, parotid, submandibular, sublingual, and lacrimal tissues. Aqp5 encodes a protein that is 98% identical to rat Aqp5. An Aqp5 antibody detects an approximately 27-kDa protein band in mouse lung, and an additional 29 kDa band in salivary gland. Cloning and physical mapping genomic fragments contiguous with Aqp5 revealed two other members of the aquaporin family: Aqp2 and Aqp6, arrayed head to tail in the order Aqp2–Aqp5–Aqp6, and provides evidence of a gene cluster conserved in order and orientation in both mice and humans.     

Aquaporin isoforms involved in physiological volume regulation of murine spermatozoa

Murine epididymal spermatozoa were dispersed in a medium of native osmolality and then transferred to a hypo-osmotic medium to mimic the physiological osmotic challenge, as encountered upon ejaculation into the female tract. The addition of quinine to block sperm K(+)-channels for volume regulation resulted in a size increase of viable cells. Preincubation in 0.1 mM HgCl(2), a standard aquaporin inhibitor, prevented such cell swelling. Addition of the K(+)-ionophore valinomycin to quinine-swollen sperm reversed the swelling, but not after pretreatment of the swollen sperm by HgCl(2). Aqp7, Aqp8, and Aqp9 mRNAs were identified in spermatozoa by RT-PCR, and the entire open reading frames were sequenced and compared with the GenBank database. Western blotting demonstrated specific protein signals for sperm AQP7 and AQP8 expression but probably not AQP9. The role of Hg(2+)-insensitive AQP7, if any, in sperm volume regulation was studied in transgenic mice. Spermatozoa from Aqp7(-/-) mice were the same size as wild-type sperm in basal conditions. Quinine-swollen volume, swelling reversal by valinomycin, and inhibition by Hg(2+) were also similar, indicating efficient water transport in the absence of AQP7. However, both water influx and efflux occurred faster in Aqp7(-/-) sperm than wild-type. This faster water movement in the knockout mouse spermatozoa was explainable by an upregulation of Aqp8 expression as revealed by quantitative PCR. Therefore, the Hg(2+)-sensitive AQP8, which was localized in elongated spermatids and spermatozoa, is a likely candidate for a water channel responsible for physiological sperm volume regulation crucial to in vivo fertilization.     

Gonadotropin-Activated Androgen-Dependent and Independent Pathways Regulate Aquaporin Expression during Teleost (Sparus aurata) Spermatogenesis

The mediation of fluid homeostasis by multiple classes of aquaporins has been suggested to be essential during spermatogenesis and spermiation. In the marine teleost gilthead seabream (Sparus aurata), seven distinct aquaporins, Aqp0a, -1aa, -1ab, -7, -8b, -9b and -10b, are differentially expressed in the somatic and germ cell lineages of the spermiating testis, but the endocrine regulation of these channels during germ cell development is unknown. In this study, we investigated the in vivo developmental expression of aquaporins in the seabream testis together with plasma androgen concentrations. We then examined the in vitro regulatory effects of recombinant piscine gonadotropins, follicle-stimulating (rFsh) and luteinizing (rLh) hormones, and sex steroids on aquaporin mRNA levels during the spermatogenic cycle. During the resting phase, when plasma levels of androgens were low, the testis exclusively contained proliferating spermatogonia expressing Aqp1ab, whereas Aqp10b and -9b were localized in Sertoli and Leydig cells, respectively. At the onset of spermatogenesis and during spermiation, the increase of androgen plasma levels correlated with the additional appearance of Aqp0a and -7 in Sertoli cells, Aqp0a in spermatogonia and spermatocytes, Aqp1ab, -7 and -10b from spermatogonia to spermatozoa, and Aqp1aa and -8b in spermatids and spermatozoa. Short-term in vitro incubation of testis explants indicated that most aquaporins in Sertoli cells and early germ cells were upregulated by rFsh and/or rLh through androgen-dependent pathways, although Aqp1ab in proliferating spermatogonia was also activated by estrogens. However, expression of Aqp9b in Leydig cells, and of Aqp1aa and -7 in spermatocytes and spermatids, was also directly stimulated by rLh. These results reveal a complex gonadotropic control of aquaporin expression during seabream germ cell development, apparently involving both androgen-dependent and independent pathways, which may assure the fine tuning of aquaporin-mediated fluid secretion and absorption mechanisms in the seabream testis.     

Human homeo box-containing genes located at chromosome regions 2q31----2q37 and 12q12----12q13

Four human homeo box-containing cDNAs isolated from mRNA of an SV40-transformed human fibroblast cell line have been regionally localized on the human gene map. One cDNA clone, c10, was found to be nearly identical to the previously mapped Hox-2.1 gene at 17q21. A second cDNA clone, c1, which is 87% homologous to Hox-2.2 at the nucleotide level but is distinct from Hox-2.1 and Hox-2.2, also maps to this region of human chromosome 17 and is probably another member of the Hox-2 cluster of homeo box-containing genes. The third cDNA clone, c8, in which the homeo box is approximately 84% homologous to the mouse Hox-1.1 homeo box region on mouse chromosome 6, maps to chromosome region 12q12----12q13, a region that is involved in chromosome abnormalities in human seminomas and teratomas. The fourth cDNA clone, c13, whose homeo box is approximately 73% homologous to the Hox-2.2 homeo box sequence, is located at chromosome region 2q31----q37. The human homeo box-containing cluster of genes at chromosome region 17q21 is the human cognate of the mouse homeo box-containing gene cluster on mouse chromosome 11. Other mouse homeo box-containing genes of the Antennapedia class (class I) map to mouse chromosomes 6 (Hox-1, proximal to the IgK locus) and 15 (Hox-3). A mouse gene, En-1, with an engrailed-like homeo box (class II) and flanking region maps to mouse chromosome 1 (near the dominant hemimelia gene). Neither of the class I homeo box-containing genes--c8 and c13--maps to a region of obvious homology to chromosomal positions of the presently known mouse homeo box-containing genes.     

猪POU1F1基因5’侧翼区克隆及序列分析

POU1F1基因是POU基因家族的成员之一,对哺乳动物的早期发育和相关基因启动表达起重要的调控作用。本文利用染色体步移技术,从长白猪基因组中首次克隆到了约1．5kb的POU1F1基因5’侧翼区序列,并利用相关软件对其进行了序列分析和物种间POU1F1基因5’侧翼区序列比对及进化树构建。结果表明所克隆的片段中含典型的TATA盒（-57）和类CAAT盒序列（-87）。TESS软件分析发现在启动子附近有一系列潜在的重要的转录因子结合位点。序列比对结果表明不同物种POU1F1基因的转录起始点上游-150bp区域保守性较强,可能是启动子的核心序列。其中猪与牛的同源性最高,其次是黑猩猩、人、狗,与大鼠、小鼠和鸡同源性较低,与斑马鱼序列同源性最低。同源序列主要集中在转录起始点上游-150bp至-1000bp区域。Vista中的MLAGAN程序构建的系统进化树真实反应了物种间进化关系。     

The role of aquaporin 3 in the movement of water and cryoprotectants in mouse morulae

The permeability to water and cryoprotectants of the plasma membrane is crucial to the successful cryopreservation of embryos. Previously, we have shown in mouse morulae that water and glycerol move across the plasma membrane by facilitated diffusion, and we have suggested that aquaporin 3 plays an important role in their movement. In the present study, we clarify the contribution of aquaporin 3 to the movement of water and various cryoprotectants in mouse morulae by measuring the Arrhenius activation energies for permeability to cryoprotectants and water, through artificial expression of aquaporin 3 using Aqp3 cRNA in mouse oocytes, and by suppressing the expression of aquaporin 3 in morulae by injecting double-stranded RNA of Aqp3 at the one-cell zygote stage. The results show that aquaporin 3 plays an important role in the facilitated diffusion of water, glycerol, and ethylene glycol, but not of acetamide and dimethylsulfoxide. On the other hand, in a propylene glycol solution, aquaporin 3 in morulae transported neither propylene glycol nor water by facilitated diffusion, probably because of strong water-solute interactions. These results provide important information for understanding the permeability of the plasma membrane of the mouse embryo.     

Pax8, a murine paired box gene expressed in the developing excretory system and thyroid gland.

Several mouse genes designated 'Pax genes' contain a highly conserved DNA sequence homologous to the paired box of Drosophila. Here we describe the isolation of Pax8, a novel paired box containing clone from an 8.5 day p.c. mouse embryo cDNA library. An open reading frame of 457 amino acids (aa) contains the 128 aa paired domain near the amino terminus. Another conserved region present in some other paired box genes, the octapeptide Tyr-Ser-Ile-Asn-Gly-Leu-Leu-Gly, is located 43 aa C-terminal to the paired domain. Using an interspecies backcross system, we have mapped the Pax8 gene within the proximal portion of mouse chromosome 2 in a close linkage to the surf locus. Several developmental mutations are located in this region. In situ hybridization was used to determine the pattern of Pax8 expression during mouse embryogenesis. Pax8 is expressed transiently between 11.5 and 12.5 days of gestation along the rostrocaudal axis extending from the myelencephalon throughout the length of the neural tube, predominantly in two parallel regions on either side of the basal plate. We also detected Pax8 expression in the developing thyroid gland beginning at 10.5 days of gestation, during the thyroid evagination. In the mesonephros and metanephros the expression of Pax8 was localized to the mesenchymal condensations, which are induced by the nephric duct and ureter, respectively. These condensations develop to functional units, the nephrons, of the kidney. These data are consistent with a role for Pax8 in the induction of kidney epithelium. The embryonic expression pattern of Pax8 is compared with that of Pax2, another recently described paired box gene expressed in the developing excretory system.