System b^0,+ absorbs lysine, arginine, ornithine, and cystine, as well as some (large) neutral amino acids in the mammalian kidney and intestine. It is a heteromeric amino acid transporter made of the heavy subunit SLC3A1/rBAT and the light subunit SLC7A9/b^0,+AT. Mutations in these two genes can cause cystinuria in mammals. To extend information on this transport system to teleost fish, we focused on the slc3a1 and slc7a9 genes by performing comparative and phylogenetic sequence analysis, investigating gene conservation during evolution (synteny), and defining early expression patterns during zebrafish (Danio rerio) development. Notably, we found that slc3a1 and slc7a9 are non-duplicated in the zebrafish genome. Whole-mount in situ hybridization detected co-localized expression of slc3a1 and slc7a9 in pronephric ducts at 24 h post-fertilization and in the proximal convoluted tubule at 3 days post-fertilization (dpf). Notably, both the genes showed co-localized expression in epithelial cells in the gut primordium at 3 dpf and in the intestine at 5 dpf (onset of exogenous feeding). Taken together, these results highlight the value of slc3a1 and slc7a9 as markers of zebrafish kidney and intestine development and show promise for establishing new zebrafish tools that can aid in the rapid screening(s) of substrates. Importantly, such studies will help clarify the complex interplay between the absorption of dibasic amino acids, cystine, and (large) neutral amino acids and the effect(s) of such nutrients on organismal growth.

系统 b ^0,+吸收赖氨酸、精氨酸、鸟氨酸和胱氨酸，以及哺乳动物肾脏和肠道中的一些（大）中性氨基酸。它是由重亚基 SLC3A1/rBAT 和轻亚基 SLC7A9/b ^0,+ AT 组成的异聚氨基酸转运蛋白。这两个基因的突变会导致哺乳动物的胱氨酸尿症。为了将有关此运输系统的信息扩展到硬骨鱼，我们通过执行比较和系统发育序列分析、研究进化过程中的基因保守性（同线性）以及定义斑马鱼 ( Danio rerio ) 发育过程中的早期表达模式，将重点放在slc3a1和slc7a9基因上。值得注意的是，我们发现slc3a1和slc7a9在斑马鱼基因组中不重复。整体原位杂交检测到slc3a1和slc7a9在受精后 24 小时前肾管和受精后 3 天 (dpf) 近曲小管中的共定位表达。值得注意的是，这两个基因在 3 dpf 的肠道原基和 5 dpf 的肠道（外源性喂养开始）的上皮细胞中均表现出共定位表达。综合起来，这些结果突出了slc3a1和slc7a9的价值作为斑马鱼肾脏和肠道发育的标志物，并有望建立有助于快速筛选底物的新型斑马鱼工具。重要的是，此类研究将有助于阐明二元氨基酸、胱氨酸和（大）中性氨基酸的吸收与此类营养素对生物体生长的影响之间复杂的相互作用。