Linser Paul J, Smith Kristin E, Seron Terri J, Neira Oviedo Marco
The University of Florida Whitney Laboratory, 9505 Ocean Shore Boulevard, St Augustine, FL 32080, USA.
J Exp Biol. 2009 Jun;212(Pt 11):1662-71. doi: 10.1242/jeb.028084.
Mosquito larvae use a digestive strategy that is relatively rare in nature. The anterior half of the larval mosquito midgut has a luminal pH that ranges between 10.5 and 11.5. Most other organisms, both large and small, initiate digestion in an acid medium. The relative uniqueness of the highly alkaline digestive strategy has been a long-standing research focus in larval lepidopterans. More recently, the disease vector potential of mosquitoes has fueled specific interest in larval mosquito biology and the alkaline digestive environment in the midgut. The probable principle anion influencing the highly alkaline gut lumen is bicarbonate/carbonate. Bicarbonate/carbonate is regulated at least in part by the activity of carbonic anhydrases. Hence, we have focused attention on the carbonic anhydrases of the mosquito larva. Anopheles gambiae, the major malaria mosquito of Africa, is an organism with a published genome which has facilitated molecular analyses of the 12 carbonic anhydrase genes annotated for this mosquito. Microarray expression analyses, tissue-specific quantitative RT-PCR, and antibody localization have been used to generate a picture of carbonic anhydrase distribution in the larval mosquito. Cytoplasmic, GPI-linked extracellular membrane-bound and soluble extracellular carbonic anhydrases have been located in the midgut and hindgut. The distribution of the enzymes is consistent with an anion regulatory system in which carbonic anhydrases provide a continuous source of bicarbonate/carbonate from the intracellular compartments of certain epithelial cells to the ectoperitrophic space between the epithelial cells and the acellular membrane separating the food bolus from the gut cells and finally into the gut lumen. Carbonic anhydrase in specialized cells of the hindgut (rectum) probably plays a final role in excretion of bicarbonate/carbonate into the aquatic environment of the larva. Detection and characterization of classic anion exchangers of the SLC4A family in the midgut has been problematic. The distribution of carbonic anhydrases in the system may obviate the requirement for such transporters, making the system more dependent on simple carbon dioxide diffusion and ionization via the activity of the enzyme.
蚊子幼虫采用一种在自然界相对罕见的消化策略。幼虫蚊子中肠的前半部分管腔pH值在10.5至11.5之间。大多数其他生物，无论大小，都在酸性介质中开始消化。这种高度碱性消化策略的相对独特性一直是幼虫鳞翅目动物长期以来的研究重点。最近，蚊子作为疾病传播媒介的潜在作用激发了人们对幼虫蚊子生物学以及中肠碱性消化环境的特别兴趣。影响高度碱性肠腔的可能主要阴离子是碳酸氢盐/碳酸盐。碳酸氢盐/碳酸盐至少部分受碳酸酐酶活性的调节。因此，我们将注意力集中在蚊子幼虫的碳酸酐酶上。冈比亚按蚊是非洲主要的疟疾传播蚊子，其基因组已公布，这有助于对该蚊子注释的12个碳酸酐酶基因进行分子分析。微阵列表达分析、组织特异性定量逆转录聚合酶链反应和抗体定位已被用于描绘碳酸酐酶在幼虫蚊子中的分布情况。细胞质、糖基磷脂酰肌醇连接的细胞外膜结合型和可溶性细胞外碳酸酐酶已定位在中肠和后肠。这些酶的分布与阴离子调节系统一致，在该系统中，碳酸酐酶从某些上皮细胞的细胞内区室向位于上皮细胞与将食物团与肠细胞分隔开的无细胞膜之间的外营养空间持续提供碳酸氢盐/碳酸盐，最终进入肠腔。后肠（直肠）特化细胞中的碳酸酐酶可能在将碳酸氢盐/碳酸盐排泄到幼虫的水生环境中起最终作用。在中肠中检测和表征SLC4A家族的经典阴离子交换体一直存在问题。该系统中碳酸酐酶的分布可能消除了对这类转运蛋白的需求，使该系统更依赖于通过酶的活性进行简单的二氧化碳扩散和离子化。
