Abstract
Aquaporins (AQP) are a family of plasma membrane proteins responsible for water transport through cell membranes. They are differentially expressed in different parts of the alimentary canal of insects where they regulate water transport. These proteins have been studied in detail in some insects, but few data are available for aquaporins of the honey bee, Apis mellifera. We used quantitative PCR to study the expression of six putative aquaporin genes in forager honey bees. We found differential expression of all putative AQP genes in crop, midgut, ileum, rectum and Malpighian tubules. We found the entomoglyceroporin Am_Eglp 1 expressed at extremely high levels in the midgut. We performed a functional characterization of Am_Eglp 1 using heterologous expression in Xenopus laevis oocyte followed by water uptake assays. Our results confirmed that the Am_Eglp 1 gene encodes a functional water transporter. This study shows that all putative honey bee aquaporin genes have complex expression patterns in the digestive and excretory organs of honey bee workers. Our results suggest that Am_Eglp 1 is the principal water transporter in the midgut of A. mellifera workers.
Highlights
Aquaporins are plasma membrane proteins facilitating water exchange between cells and their surroundings
In this study we show the relative expression of six putative aquaporin genes in distinct parts of the digestive tract and Malpighian tubules of A. mellifera workers and present the functional characterization of Am_Eglp 1
We performed qPCR analysis for six putative A. mellifera aquaporin genes
Summary
Aquaporins are plasma membrane proteins facilitating water exchange between cells and their surroundings. They were first discovered in mammalian cells [1,2,3,4]. Aquaporins have been found in almost every living organism [5]. These proteins have six conserved hydrophobic transmembrane domains connected by five hydrophilic loops [6]. Sequence analysis revealed high conservation in the transmembrane domains [7, 8]. Two of the loops contain conserved NPA motifs (asparagine, proline, alanine) which form the center of the water channel pore [3]. The presence of a cysteine residue close to the second NPA motif is critical for this Hg sensitivity [8, 9]
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