Estrada G, Krasinski S D, Montgomery R K, Grand R J, García-Valero J, López-Tejero M D
Department de Bioquímica i Fisiologia, Universitat de Barcelona, Spain.
J Cell Physiol. 1996 May;167(2):341-8. doi: 10.1002/(SICI)1097-4652(199605)167:2<341::AID-JCP19>3.0.CO;2-A.
At birth, the mammalian small intestine displays regional differences in morphology as well as complex proximal-to-distal (horizontal) patterns of protein distribution. Lactase-phlorizin hydrolase (LPH), an enterocyte-specific disaccharidase crucial for the digestion of lactose in milk, reveals a characteristic horizontal pattern of expression at birth. However, it is not certain whether this topographic pattern is due to variations in epithelial structure along the length of the small intestine or to regional differences in the transcription of the LPH gene. In order to understand the mechanisms that regulate the regionalization of LPH at birth, we characterized the epithelial structure along the horizontal axis using stereologic techniques and correlated these data with the patterns of lactase activity and LPH mRNA abundance in the small intestine of unsuckled, newborn rats. Epithelial volume and microvillar surface area per unit of intestinal length decreased three-to fourfold from duodenum to distal ileum. In contrast, lactase activity and LPH mRNA abundance were highest in proximal jejunum and lowest in the most proximal and distal ends of the small intestine. Mean lactase activity per cell in proximal duodenum, proximal jejunum, and distal ileum was estimated at 12.0, 26.7, and 5.6 nU/absorptive enterocyte, respectively, and paralleled the concentration of LPH mRNA in the same segments: 20, 45, and 15 molecules of LPH mRNA/absorptive enterocyte. Our data indicate that horizontal gradients of lactase activity in the newborn rat intestine do not depend on epithelial organization or on enteral factors, since the horizontal gradient is established before suckling. Each absorptive enterocyte along the small intestine expresses lactase activity in a position-dependent manner which is controlled at the level of mRNA abundance.
出生时，哺乳动物的小肠在形态上呈现出区域差异，同时蛋白质分布也呈现出复杂的从近端到远端（水平）模式。乳糖酶 - 根皮苷水解酶（LPH）是一种肠上皮细胞特异性双糖酶，对牛奶中乳糖的消化至关重要，在出生时呈现出特征性的水平表达模式。然而，尚不确定这种拓扑模式是由于小肠长度上上皮结构的差异，还是由于LPH基因转录的区域差异。为了了解出生时调节LPH区域化的机制，我们使用体视学技术对小肠横轴上的上皮结构进行了表征，并将这些数据与未哺乳新生大鼠小肠中的乳糖酶活性模式和LPH mRNA丰度相关联。从十二指肠到回肠末端，单位肠长度的上皮体积和微绒毛表面积减少了三到四倍。相比之下，乳糖酶活性和LPH mRNA丰度在空肠近端最高，在小肠最近端和最远端最低。估计十二指肠近端、空肠近端和回肠末端每个细胞的平均乳糖酶活性分别为12.0、26.7和5.6 nU/吸收性肠上皮细胞，并且与相同节段中LPH mRNA的浓度平行：20、45和15个LPH mRNA分子/吸收性肠上皮细胞。我们的数据表明，新生大鼠小肠中乳糖酶活性的水平梯度不依赖于上皮组织或肠内因子，因为这种水平梯度在哺乳前就已建立。小肠沿线的每个吸收性肠上皮细胞以位置依赖的方式表达乳糖酶活性，这在mRNA丰度水平上受到控制。
