More than hemoglobin – the unexpected diversity of globins in vertebrate red blood cells

Abstract

<p>In many multicellular organisms, oxygen is transported by respiratory proteins,</p><p> </p><p>which are globins in vertebrates, between respiratory organs and tissues.</p><p> </p><p>In jawed vertebrates, eight globins are known which are expressed in a highly</p><p> </p><p>tissue-specific manner. Until now, hemoglobin (Hb) had been agreed to be</p><p> </p><p>the only globin expressed in vertebrate erythrocytes. Here, we investigate for</p><p> </p><p>the first time the mRNA expression of globin genes in nucleated and anucleated</p><p> </p><p>erythrocytes of model vertebrate species by quantitative real-time reverse</p><p> </p><p>transcription PCR (qRT-PCR). Surprisingly, we found transcripts of the whole</p><p> </p><p>gnathostome globin superfamily in RBCs. The mRNA expression levels varied</p><p> </p><p></p><p>among species, with Hb being by far the dominant globin. Only in stickleback,</p><p> </p><p>a globin previously thought to be neuron-specific, neuroglobin, had higher</p><p> </p><p>mRNA expression. We furthermore show that in birds transcripts of globin E,</p><p></p><p></p><p> </p><p>which was earlier reported to be transcribed only in the eye, are also present</p><p> </p><p>in RBCs. Even in anucleated RBCs of mammals, we found transcripts of myoglobin,</p><p> </p><p>neuroglobin, and cytoglobin. Our findings add new aspects to the current</p><p> </p><p>knowledge on the expression of globins in vertebrate tissues. However,</p><p> </p><p>whether or not the mRNA expression of these globin genes has any functional</p><p> </p><p>significance in RBCs has to be investigated in future studies.</p><p></p><p><br /></p>