低亲和力钠依赖二羧基转运蛋白随增龄表达变化的研究

目的 研究大鼠及人类肾脏低亲和力钠依赖(Na~+/)二羧基转运蛋白(NaDC1)随增龄的表达变化规律并探讨其在肾脏衰老变化中的意义。方法 采用Northern杂交、Western印迹及免疫组化等方法对大鼠出生后1d、7d、1个月、3个月、12个月、24个月及少年、中青年、老年正常人肾脏 NaDC1的表达变化。结果 大鼠NaDC1 mRNA表达呈现随肾组织发育成熟表达逐渐增强,1个月达高峰,后随增龄表达下降的趋势(P<0.05)。Western印迹显示NaDC1蛋白随鼠龄增高表达逐渐增强,3个月达高峰,后表达渐降的趋势。免疫组化结果显示大鼠及人类肾组织NaDC1分别表达于近端小管刷状缘,大鼠生后1d表达最弱,后表达渐强,到3个月达高峰(5.30±1.52比1.40±0.43,P<0.01),后呈现渐降的趋势(P<0.05)。人类肾组织NaDC1表达呈现随增龄渐降的趋势。结论 大鼠及人肾组织进入衰老时,NaDC1 mRNA及蛋白表达均呈现下降的趋势,可作为对肾脏衰老观察的指标之一。     

缺血再灌注损伤后肾小管上皮细胞的衰老演变及其意义

目的观察肾脏缺血再灌注损伤（IRI）后正常和衰老肾小管上皮细胞的演变，探讨细胞衰老在衰老相关性肾脏病理变化中的作用。方法以低龄（2月龄）和高龄（12月龄）野生鼠为研究对象。建立左肾IRI模型。于IRI后0d、1d、3d、7d、1月、3月、6月取肾组织，用HE染色观察肾小管组织学变化；免疫组织化学检测肾小管上皮细胞增殖细胞核抗原（PCNA）的表达；组织化学染色观察肾小管上皮细胞衰老相关β-半乳糖苷酶（SA-β-gal）的活性；TUNEL法检测凋亡肾小管上皮细胞。结果肾脏IRI后0d，肾小管以坏死为主，高龄鼠比低龄鼠更为明显（P〈0．05）。IRI1d后出现肾小管上皮细胞凋亡，7d凋亡达到高峰（P〈0．05），且在同一时间点，高龄鼠比低龄鼠严重（P〈0．05）。低龄鼠IRI肾1月时出现肾小管上皮细胞衰老，而对侧肾没有出现，3月、6月点衰老细胞显著增多（P〈0．05）；高龄鼠IRI后0d双肾均可见大量衰老的肾小管上皮细胞，但IRI肾的衰老细胞在IRIld后明显减少（P〈0．05），1月后又逐渐增多。6月后高龄鼠双肾衰老的肾小管上皮细胞几乎又达到同一水平。PCNA阳性染色细胞出现的几率两组相比差异无统计学意义（P〉0．05），但低龄组细胞增殖能力要强于高龄组。对高龄鼠IRI后1d点肾小管上皮细胞凋亡与衰老之间的相关分析显示，二者存在显著负相关（r=-0．82,P〈0．001）。结论IRI可促进正常肾小管上皮细胞衰老的进程。已经进入衰老状态的肾小管上皮细胞在遭受IRI刺激后，更易走向死亡[坏死和（或）凋亡]。肾小管上皮细胞的这种演变，在老化相关性肾脏病理变化发生和进展中可能发挥着重要作用。     

中国实验用小型猪肾小管的发育及各节段标志物的表达

目的:明确解剖和生理上与人非常接近的中国实验用小型猪肾脏发育过程中肾小管的形态学变化和肾小管各节段的特异性标志物。方法:采用高碘酸-希夫(PAS)染色和免疫荧光染色技术,系统观察中国实验用小型猪妊娠28～112d(E28d～E112d)和出生后1d、7d、14d、21d(P1d～21d),共17个不同时间点猪肾小管的发育及肾小管特异性标志物雪莲花凝集素(LTL)、水通道蛋白1(AQP1)、钙结合蛋白(calbindin)-D28k在肾小管不同节段的表达。结果:(1)中国实验用小型猪E28d可见后肾间充质和输尿管芽,即后肾已经开始发育;但这时还没有肾小管。E35d可见不同节段的肾小管,即肾小管已开始发育。从E35d～P14d(E112d仔猪出生),肾皮质均有生肾区存在,即不断有新的肾单位发生;P21d生肾区消失,即不再有新的肾单位产生。(2)①LTL在E28d表达在输尿管芽,E35d开始在近端小管表达,以刷状缘表达最为明显;表达由弱到强,由点状到线状。②AQP1在E28d未见表达,E35d开始表达;AQP1表达在近端小管和髓袢的降支细段,主要表达在细胞膜,尤其在管腔侧的表达更为明显。③Calbindin-D28k在E28d表达在输尿管芽,E35d开始表达在远端小管和集合管;Calbindin-D28k主要表达在细胞质,随着肾小管发育,表达逐渐增强。(3)发现集合管来源于输尿管芽,发源于输尿管芽的集合管从被膜下的生肾区一直延伸到肾髓质。结论:中国实验用小型猪妊娠35d可以见到不同节段肾小管。LTL、AQP1、Calbindin-D28k可以分别作为猪近端小管、髓袢、远端小管和集合管的标志物。     

intermedin预处理对大鼠肾脏缺血再灌注损伤修复和再生过程的作用

目的 探讨intermedin （IMD）预处理对大鼠肾脏缺血再灌注（IR）损伤修复和再生过程的作用。 方法 将Wistar大鼠按随机数字表法分为4组：假手术组（sham）、IR组、转空质粒组和转IMD组。在切除右肾后,转IMD组用超声微泡造影剂介导的基因转染方法将IMD真核质粒转染到大鼠肾组织,用RT-PCR和Western印迹法检测转染效率。转染成功后,制作肾脏IR损伤模型,分别于再灌注后1 d、2 d、3 d、4 d、7 d和14 d 6个时间点各取6只大鼠,留取血清及肾组织标本,常规检测血清BUN和Scr;HE和PAS染色观察肾组织的病理变化;免疫组化法观察肾小管上皮细胞的增殖程度。 结果 （1）转IMD组比转空质粒组的IMD蛋白和mRNA表达均增多（均P < 0.05）,且转IMD组7 d时表达最多,与转IMD组4 d时差异无统计学意义;（2）与sham组相比,IR组1 d和2 d时Scr和BUN均显著增高（P < 0.05）;与IR组相比,转IMD组显著下降（P < 0.05）;转空质粒组与IR组相比差异无统计学意义（P > 0.05）。（3）IR组、转空质粒组和转IMD组大鼠的肾小管均受损,但转IMD组的损伤较轻,均以2 d时病理损伤最重。（4）sham组肾小管和肾小球内几乎没有增殖细胞核抗原（PCNA）阳性细胞的表达;IR组和转空质粒组的PCNA阳性数在IR损伤1 d时开始增加,7 d时最多;转IMD组的PCNA阳性细胞数在IR损伤1 d时开始增加,3 d时最多。与IR组1~4 d相比,转IMD组的PCNA阳性细胞数显著增加（P < 0.05）;与IR组7 d相比,转IMD组7 d的PCNA阳性细胞数显著减少（P < 0.05）。 结论 IMD预处理可以促进肾小管上皮细胞增殖,加速肾脏IR损伤修复和再生。     

中性粒细胞明胶酶相关脂质运载蛋白对大鼠肾脏缺血再灌注损伤肾小管上皮细胞的保护作用

目的 探讨中性粒细胞明胶酶相关脂质运载蛋白(NGAL)对大鼠缺血再灌注损伤肾脏肾小管上皮细胞凋亡的保护作用及机制.方法 建立大鼠肾脏缺血再灌注模型,雄性SD大鼠随机分为对照组、缺血再灌注模型组、NGAL组 ;HE染色观察3组大鼠肾组织病理变化 ;TUNEL法检测肾小管上皮细胞凋亡 ;实时定量PCR、Western印迹法检测凋亡蛋白fas、bcl-2的表达变化.结果 与缺血再灌注模型组比较,NGAL组肾小管上皮细胞凋亡数量显著减少[(8.6±3.4)/HP比(20.8±3.7)/HP,P＜0.05] ;NGAL组肾组织fas mRNA(2.34±0.51比6.84±2.34,P＜0.05)、fas蛋白(0.65±0.05比0.95±0.08,P＜0.05)表达显著下调,bcl-2蛋白(0.33±0.05比0.24±0.03,P＜0.05)表达显著上调,但bcl-2 mRNA表达无明显改变.结论 NGAL对大鼠缺血再灌注损伤肾小管上皮细胞有保护作用,其作用可能与减少细胞凋亡、改变凋亡蛋白的表达有关.     

骨髓间质干细胞对大鼠急性肾小管损伤修复的促进作用

目的 观察骨髓间质干细胞(MSCs)对氯化汞(HgCl2)导致的急性肾小管损伤有无治疗作用，并探讨其可能的机制。 方法 建立HgCl2腹腔注射导致大鼠急性肾衰竭模型。SD大鼠分为MSCs组(HgCl2+MSCs)、生理盐水组(HgCl2+生理盐水)及正常对照组。7 d后，观察体重、生存率、肾功能、肾脏病理改变，进行增殖细胞核抗原(PCNA)、巨噬细胞标志物ED-1和增强绿色荧光融合蛋白(EGFP)免疫组织化学染色，用RT-PCR技术检测肾组织内细胞因子的表达情况，并观察EGFP转基因的MSCs在肾脏的分布情况。 结果 MSCs组在体重、生存率、肾功能、肾脏病理改变上，均明显好于生理盐水组；肾组织内PCNA+及ED-1+细胞数明显少于生理盐水组；促进肾小管损伤修复的生长因子表皮生长因子(EGF)、血小板源生长因子(PDGF)、肝细胞生长因子(HGF)在肾组织内表达明显高于生理盐水组，而促炎症因子TNF-α则明显低于生理盐水组。7 d时，间质干细胞在肾间质中偶尔可见到，而肾小管中未见。 结论 MSCs输注可促进HgCl2所致的急性肾小管损伤的修复，其作用机制可能是通过调节肾组织中细胞因子的分泌起作用，而非完全依靠转分化成肾小管上皮细胞。     

前列腺癌与前列腺增生Ki-67/PCNA mRNA特异性表达比值的研究

目的 以实时荧光定量RT-PCR技术研究良性前列腺增生(BPH)与前列腺癌(PCa)组织标本Ki-67蛋白和组织核增殖抗原(PCNA)mRNA的比值,探讨此比值在PCa诊断中的特异性意义.方法 通过实时荧光定量RT-PCR检测63例PCa和37例BPH前列腺组织Ki-67/PCNAmRNA的表达,比较其在PCa与BPH组织中定量的差异.结果 BPH与PCa组织Ki-67/PCNA mRNA的定量表达值分别为2.264±0.460与5.905±0.780,差异有统计学意义(P＜0.05).结论 实时荧光定量RT-PCR检测Ki-67/PCNA mRNA为PCa的诊断提供了可靠的辅助指标.     

骨调素和单核细胞趋化蛋白在大鼠梗阻性肾病中的表达及可能作用

目的:探讨骨调素(OPN)和单核细胞趋化蛋白(MCP-1)在大鼠梗阻性模型中的表达及其在肾脏纤维化发病机制中的作用.方法:采用-单侧输尿管结扎制造梗阻性肾病模型,分别于造模后7 d、14 d取肾组织,应用HE染色观察肾脏病理改变,免疫组化方法检测肾组织畔OPN和MCP-1蛋白的表达,应用逆转录-聚合酶链式反应(RT-PCR)法观察肾组织中OPN mRNA和MCP-1 mRNA的变化.结果:OPN、MCP-1表达主要位于肾小管上皮细胞,随着梗阻时间的延长,肾组织中OPN、MCP-1蛋白和mRNA表达明显增加.结论:OPN、MCP-1蛋白和mRNA在梗阻性肾病大鼠肾组织表达明显增加介导炎症过程,参与肾间质纤维化.     

核因子-κB在狼疮肾炎肾组织中的表达及其意义

目的了解狼疮肾炎(LN)肾组织中核因子(NP)-κB的表达并探讨其与LN肾脏病理改变和肾功能损害的关系.方法以NF-κB亚基P65单抗为抗体,采用微波免疫组织化学染色(APAAP法)检测LN肾组织NF-κB表达,并进一步分析其与肾小球内C-myc蛋白表达、LN活动指数、肾脏病理和功能损害的关系.结果狼疮肾炎肾组织中NF-κB表达较正常肾组织显著增高,以WHOⅣ型为最显著.NF-κB在肾小球和肾小管均有表达,但小管表达更显著.LN肾组织NF-κB阳性细胞数与肾小球C-myc蛋白表达量、肾组织活动指数、肾脏病理改变和肾功能损害显著相关.结论NF-κB可能参与了LN的发病机制,肾组织中NF-κB的表达可作为反映狼疮肾组织活动病变和进行性肾损害的参考指标.     

内质网应激相关凋亡途径参与单侧输尿管梗阻大鼠肾间质纤维化

目的 探讨内质网应激（ERS）相关凋亡途径在单侧输尿管梗阻（UUO）大鼠肾间质纤维化发生、发展中的作用。 方法 健康雄性Wistar大鼠25只,按随机数字表法分为UUO模型组（n=18）和假手术组（n=7）,UUO模型组行左侧输尿管结扎术,假手术组仅分离输尿管不结扎,分别于术后3 d、7 d、14 d处死各组大鼠,行HE和Masson染色,观察肾脏病理变化;比色法测定肾组织羟脯氨酸（HYP）含量;免疫组化法检测α平滑肌肌动蛋白（α-SMA）;原位末端标记法（TUNEL）与DNA电泳观察肾小管间质细胞凋亡情况;RT-PCR法检测梗阻侧肾组织ERS相关分子葡萄糖调节蛋白78（GRP78）mRNA表达变化;Western印迹法分析凋亡相关蛋白半胱氨酸天门冬氨酸蛋白酶3（caspase-3）和GRP78的蛋白表达变化。 结果 与假手术组比较,UUO模型组肾脏病理改变加重,肾间质纤维化程度随梗阻时间延长逐渐加重,肾组织HYP含量显著升高（P < 0.05）,肾组织α-SMA也在肾小管间质细胞广泛表达,TUNEL染色及DNA琼脂糖凝胶电泳提示大量的肾小管间质细胞凋亡。UUO模型组GRP78 mRNA表达于术后3 d即发生显著上调,而蛋白表达在术后7 d开始出现显著变化,与假手术组差异均有统计学意义（均P < 0.01）;在此后观察期间内GRP78 mRNA和蛋白均持续高水平表达。模型组大鼠肾组织caspase-3的蛋白表达在UUO术后3 d即有显著上调（P < 0.05）,且随着梗阻时间延长进行性升高,于术后7 d、14 d增多更为显著,与假手术组差异均有统计学意义（P < 0.05）。相关分析显示GRP78蛋白表达与肾组织HYP含量和caspase-3蛋白表达均呈正相关（r = 0.657,P < 0.01;r = 0.714,P < 0.01）。 结论 UUO早期即可诱导ERS标志蛋白表达变化,触发ERS。长期ERS可诱导肾小管间质细胞凋亡;caspase-3介导的ERS相关凋亡途径可能参与了肾间质纤维化过程。     

Development of lymphatic vasculature and morphological characterization in rat kidney

Background

The mechanisms and morphological characteristics of lymphatic vascular development in embryonic kidneys remain uncertain.

Methods

We examined the distribution and characteristics of lymphatic vessels in developing rat kidneys using immunostaining for podoplanin, prox-1, Ki-67, type IV collagen (basement membrane: BM), and ??-smooth muscle actin (??SMA: pericytes or mural cells). We also examined the expression of VEGF-C.

Results

At embryonic day 17 (E17), podoplanin-positive lymphatic vessels were observed mainly in the kidney hilus. At E20, lymphatic vessels extended further into the developing kidneys along the interlobar vasculature. In 1-day-old pups (P1) to P20, lymphatic vessels appeared around the arcuate arteries and veins of the kidneys, with some reaching the developing cortex via interlobular vessels. In 8-week-old adult rats, lymphatic vessels were extensively distributed around the blood vasculature from the renal hilus to cortex. Only lymphatic capillaries lacking continuous BM and ??SMA-positive cells were present within adult kidneys, with none observed in renal medulla. VEGF-C was upregulated in the developing kidneys and expressed mainly in tubules. Importantly, the developing lymphatic vessels were characterized by endothelial cells immunopositive for podoplanin, prox-1, and Ki-67, with no surrounding BM or ??SMA-positive cells.

Conclusion

During nephrogenesis, lymphatic vessels extend from the renal hilus into the renal cortex along the renal blood vasculature. Podoplanin, prox-1, Ki-67, type IV collagen, and ??SMA immunostaining can detect lymphatic vessels during lymphangiogenesis.     

Expression of p16INK4a and other cell cycle regulator and senescence associated genes in aging human kidney

BACKGROUND: Somatic cells in vitro have a finite life expectancy before entering a state of senescence. If this state has an in vivo counterpart, it could contribute to organ aging. We have previously shown that human kidney cortex displays telomere shortening with age. In the present study, we evaluated the relationship between renal age in humans and a number of phenomena associated with cellular senescence in vitro. METHODS: Human kidney specimens were obtained at 8 weeks to 88 years of age and were assessed for changes related to aging. RESULTS: We found that human kidneys expressed relatively constant levels of mRNAs for genes potentially related to senescence. Among the candidate genes surveyed, the cell cycle regulator p16INK4a emerged with the strongest association with renal aging for both mRNA and protein expression. Proliferation as measured by Ki-67 expression was inversely correlated with p16INK4a expression, compatible with a role for p16INK4a as an irreversible cell cycle inhibitor. Cyclooxygenase 1 and 2 (COX-1 and COX-2) mRNA expression was elevated in older kidneys, associated with increased protein expression. Comparison of gene expression with age-related histologic changes revealed that glomerulosclerosis correlated with p16INK4a and p53, whereas interstitial fibrosis and tubular atrophy were associated with p16INK4a, p53, COX-1, transforming growth factor-beta 1 (TGF-beta 1), and heat shock protein A5 (HSPA5). CONCLUSION: We conclude that some changes observed in cellular senescence in vitro do occur in human kidney with age, particularly in the renal cortex, in some cases correlating with histologic features. P16INK4a emerged with the most consistent correlations with age and histologic changes and inversely correlated with cell replication.     

Kidney injury molecule-1 expression in transplant biopsies is a sensitive measure of cell injury

Kidney injury molecule-1 (KIM-1) is a specific histological biomarker for diagnosing early tubular injury on renal biopsies. In this study, KIM-1 expression was quantitated in renal transplant biopsies by immunohistochemistry and correlated with renal function. None of the 25 protocol biopsies showed detectable tubular injury on histologic examination, yet 28% had focal positive KIM-1 expression. Proximal tubule KIM-1 expression was present in all biopsies from patients with histological changes showing acute tubular damage and deterioration of kidney function. In this group, higher KIM-1 staining predicted a better outcome with improved blood urea nitrogen (BUN), serum creatinine, and estimated glomerular filtration rate (eGFR) over an ensuing 18 months. KIM-1 was expressed focally in affected tubules in 92% of kidney biopsies from patients with acute cellular rejection. By contrast, there was little positive staining for Ki-67, a cell proliferation marker, in any of the groups. KIM-1 expression significantly correlated with serum creatinine and BUN, and inversely with the eGFR on the biopsy day. Our study shows that KIM-1 staining sensitively and specifically identified proximal tubular injury and correlated with the degree of renal dysfunction. KIM-1 expression is more sensitive than histology for detecting early tubular injury, and its level of expression in transplant biopsies may indicate the potential for recovery of kidney function.     

Expression of the type IV collagenase system during mouse kidney development and tubule segmentation.

Type IV collagenases matrix metalloproteinase-2 (MMP2) and MMP9 and their related proteins, MT1-MMP, tissue inhibitor of metalloproteinases 1 (TIMP1), TIMP2, and TIMP3, are expressed during kidney morphogenesis and nephrogenesis, but the renal ontogeny of these proteins is only partially known, and their persistence in the adult remains controversial. Their expression was analyzed from early metanephric stages to adulthood by Western blot semiquantitative analysis; laser confocal microscopy of whole-mount kidneys; and a two-step immunoperoxidase labeling procedure using specific markers of proximal tubule (megalin), ascending limb of Henle's loop (Tamm Horsfall protein), and collecting duct (Dolichos biflorus agglutinin lectin). By Western blot, all antigens were detected at day 11.5, peaked at day 16.5, and persisted in the adult at lower levels, although MMP2 was less modulated. All antigens were expressed in metanephric mesenchyme at embryonic day 11.5 and became concentrated in neural cell adhesion molecule-positive-induced mesenchymal cells at day 12.5. Only MT1-MMP and to a lesser extent MMP2 were detected in the ureter bud. At day 16.5, all antigens predominated in the cytoplasm of the proximal tubule, except TIMP1, which was mostly expressed in the ascending limb of Henle's loop and distal tubule. During tubule segmentation, components of the type IV collagenase system showed both spatial and temporal regulation. The distribution of gelatinases was not strictly superimposable to that of their natural inhibitors TIMP, especially for MMP9 and TIMP1. All components persisted in specific segments of the adult renal tubule, where MMP9, MMP2, and MT1-MMP showed an apical expression, suggesting that substrates for these enzymes should be in the tubule lumen or in the apical cell domain and not in the extracellular matrix. These results suggest that a regulated balance of gelatinase activity is required during kidney organogenesis and that gelatinases continue to play a role in adult renal tubule physiology.     

Early embryonic renal tubules of wild-type and polycystic kidney disease kidneys respond to cAMP stimulation with cystic fibrosis transmembrane conductance regulator/Na(+),K(+),2Cl(-) Co-transporter-dependent cystic dilation

Metanephric organ culture has been used to determine whether embryonic kidney tubules can be stimulated by cAMP to form cysts. Under basal culture conditions, wild-type kidneys from embryonic day 13.5 to 15.5 mice grow in size and continue ureteric bud branching and tubule formation over a 4- to 5-d period. Treatment of these kidneys with 8-Br-cAMP or the cAMP agonist forskolin induced the formation of dilated tubules within 1 h, which enlarged over several days and resulted in dramatically expanded cyst-like structures of proximal tubule and collecting duct origin. Tubule dilation was reversible upon withdrawal of 8-Br-cAMP and was inhibited by the cAMP-dependent protein kinase inhibitor H89 and the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR(inh)172. For further testing of the role of CFTR, metanephric cultures were prepared from mice with a targeted mutation of the Cftr gene. In contrast to kidneys from wild-type mice, those from Cftr -/- mice showed no evidence of tubular dilation in response to 8-Br-cAMP, indicating that CFTR Cl(-) channels are functional in embryonic kidneys and are required for cAMP-driven tubule expansion. A requirement for transepithelial Cl(-) transport was demonstrated by inhibiting the basolateral Na(+),K(+),2Cl(-) co-transporter with bumetanide, which effectively blocked all cAMP-stimulated tubular dilation. For determination of whether cystic dilation occurs to a greater extent in PKD kidneys in response to cAMP, Pkd1(m1Bei) -/- embryonic kidneys were treated with 8-Br-cAMP and were found to form rapidly CFTR- and Na(+),K(+),2Cl(-) co-transporter-dependent cysts that were three- to six-fold larger than those of wild-type kidneys. These results suggest that cAMP can stimulate fluid secretion early in renal tubule development during the time when renal cysts first appear in PKD kidneys and that PKD-deficient renal tubules are predisposed to abnormally increased cyst expansion in response to elevated levels of cAMP.     

Immunocytochemical localization of ferritin in the kidney and renal tumours

The distribution of ferritin in the kidney and renal tumors was studied using a polyclonal anti-ferritin antiserum and immunocytochemical techniques. Ten fetal kidneys, 5 adult kidneys and 56 renal tumours were studied. Ferritin first appears in the maturing fetal nephron where it is confined to the proximal tubule. In the adult kidney ferritin is also restricted to the proximal tubule. Ferritin was not seen in 18 nephroblastomas nor in 4 renal sarcomas, but 14 of 26 renal cell carcinomas and 5 of 8 renal oncocytomas contained ferritin. The relationship between the expression of ferritin and tumour differentiation is discussed.     

Organic anion and cation transporter expression and function during embryonic kidney development and in organ culture models

Organic anion and cation transporters (OATs, OCTs, and OCTNs) mediate the proximal tubular secretion of numerous clinically important compounds, including various commonly prescribed pharmaceuticals. Here, we report determination of the ontogeny of these transporters and of NaP(i)2 and SGLT1, using quantitative polymerase chain reaction (QPCR) to determine expression levels of transporter genes in rat embryonic kidneys on each day of gestation from embryonic day (ed) 13 to ed18, in cultures of induced and uninduced metanephric mesenchyme (MM), and on each day of 1 week of whole embryonic kidney (WEK) culture. We also examined ontogeny of Oat1 protein expression in rat embryonic kidney by immunohistochemistry. Finally, we used uptake of fluorescein (FL) as a novel in vitro functional assay of OAT expression in WEK and MM. Developmental induction of OAT and OCT genes does not occur uniformly: some genes are induced early (e.g., Oat1 and Oat3, potential early markers of proximal tubulogenesis), and others after kidney development is relatively advanced (e.g., Oct1, a potential marker of terminal differentiation). The ontogeny of transporter genes in WEK and MM is similar to that observed in vivo, indicating that these organ culture systems may represent convenient in vitro models to study the developmental induction of OATs, OCTs, and OCTNs. Functional transport was evidenced by accumulation of FL in the developing tubule in WEK and MM organ cultures. Our findings on the renal ontogeny of OATs and OCTs could carry implications both for the development of more rational therapeutics for premature infants, as well as for our understanding of proximal tubule differentiation.