BOA, INRA, Université de Tours, 37380 Nouzilly, France.
GeT-PlaGe, INRA, Auzeville, 31326 Castanet-Tolosan, France.
Poult Sci. 2019 Nov 1;98(11):6005-6018. doi: 10.3382/ps/pez407.
To meet the high calcium (Ca) demand during eggshell biomineralization (2 g of Ca per egg), laying hens develop specific metabolic regulations to maintain Ca homeostasis. The intake of Ca, its solubilization, and absorption capacity are enhanced at sexual maturity (SM). A better knowledge of the intestinal Ca transporters involved in their variations at this stage could indicate new nutritional strategies to enhance Ca digestive utilization. Transcellular Ca absorption pathway and its major player calbindin-D 28 K (CALB1) mediate a saturable transport, which has been extensively described in this model. Conversely, a contribution by the paracellular pathway involving non-saturable Ca transport through intercellular tight junction has also been suggested. The aim of the present study was to identify candidate genes of these two pathways and their patterns of expression, in immature pullets (12, 15, and 17 wk old) and mature laying hens (23 wk old) in the duodenum, jejunum, and ileum. Using RT-qPCR, this study identifies 3 new candidate genes for transcellular, and 9 for paracellular Ca transport. A total of 5 candidates of the transcellular pathway, transient receptor potential cation channels subfamily C member 1 (TRPC1) and M member 7 (TRPM7); CALB1 and ATPase plasma membrane Ca2+ transporting 1 (ATP2B1) and ATPase plasma membrane Ca2+ transporting 2 (ATP2B2) were enhanced with age or after SM in the duodenum, the jejunum or all 3 segments. A total of 4 candidates of the paracellular pathway Claudin 2 (CLDN2) and tight junction proteins 1, 2, and 3 (TJP1, TJP2 and TJP3) increased in the small intestine after SM. Additionally, CALB1, ATP2B2, and CLDN2 were overexpressed in the duodenum or the jejunum or both segments after SM. The enhanced expression of candidate genes of the paracellular Ca pathway after SM, supports that the non-saturable transport could be a mechanism of great importance when high concentrations of soluble Ca are observed in the intestinal content during eggshell formation. Both pathways may work cooperatively in the duodenum and jejunum, the main sites of Ca absorption in laying hens.
为了满足蛋壳生物矿化过程中对高钙（Ca）的需求（每枚蛋 2 克 Ca），产蛋母鸡会发展出特定的代谢调节机制来维持 Ca 体内平衡。在性成熟（SM）时，Ca 的摄入、溶解和吸收能力会增强。更好地了解肠道 Ca 转运体在这一阶段的变化，可能会为提高 Ca 消化利用率提供新的营养策略。细胞旁 Ca 转运途径及其主要参与者钙结合蛋白-D28K（CALB1）介导了一种可饱和的转运，该转运在该模型中已得到广泛描述。相反，通过细胞间紧密连接的非饱和 Ca 转运也暗示了细胞旁途径的贡献。本研究的目的是在十二指肠、空肠和回肠中鉴定不成熟育雏鸡（12、15 和 17 周龄）和成熟产蛋母鸡（23 周龄）中这两种途径的候选基因及其表达模式。本研究使用 RT-qPCR 鉴定了细胞旁 Ca 转运的 3 个新候选基因和 9 个候选基因。细胞旁途径的 5 个候选基因，瞬时受体电位阳离子通道亚家族 C 成员 1（TRPC1）和 M 成员 7（TRPM7）；钙结合蛋白-D28K（CALB1）和质膜 Ca2+ATP 酶 1（ATP2B1）和质膜 Ca2+ATP 酶 2（ATP2B2）在十二指肠、空肠或 3 个肠段均随着年龄或性成熟而增加。细胞旁途径的 4 个候选基因紧密连接蛋白 2（CLDN2）和紧密连接蛋白 1、2 和 3（TJP1、TJP2 和 TJP3）在小肠 SM 后增加。此外，SM 后在十二指肠或空肠或两个肠段均过度表达了 CALB1、ATP2B2 和 CLDN2。SM 后细胞旁 Ca 转运途径候选基因的表达增强，表明当蛋壳形成过程中肠内容物中存在高浓度可溶性 Ca 时，非饱和转运可能是一种非常重要的机制。这两种途径可能在十二指肠和空肠中协同作用，因为这是产蛋母鸡 Ca 吸收的主要部位。
