Dark side of the epididymis: tails of sperm maturation

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>The Hermes body (<jats:styled-content style="fixed-case">HB</jats:styled-content>) previously called the cytoplasmic droplet is a focal distension of the flagellar cytoplasm of epididymal spermatozoa consisting mainly of isolated flattened Golgi cisternae.</jats:p></jats:sec><jats:sec><jats:title>Objective</jats:title><jats:p>To define a functional role for the <jats:styled-content style="fixed-case">HB</jats:styled-content> of epididymal spermatozoa.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Isolated fractions of <jats:styled-content style="fixed-case">HB</jats:styled-content>s of epididymal spermatozoa were prepared and by quantitative tandem mass spectrometry revealed 1511 proteins.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The glucose transporter <jats:styled-content style="fixed-case">GLUT</jats:styled-content>‐3 was the most abundant protein followed by hexokinase 1, which along with the presence of all glycolytic enzymes suggested a role for the <jats:styled-content style="fixed-case">HB</jats:styled-content> in glycolysis. Several <jats:styled-content style="fixed-case">TMED</jats:styled-content>/p24 Golgi trafficking proteins were abundant with <jats:styled-content style="fixed-case">TMED</jats:styled-content>7/p27 and <jats:styled-content style="fixed-case">TMED</jats:styled-content>2/p24 defining the identity of the flattened cisternae within the <jats:styled-content style="fixed-case">HB</jats:styled-content> as Golgi, along with the known Golgi proteins, <jats:styled-content style="fixed-case">GBF</jats:styled-content>1, <jats:styled-content style="fixed-case">GOLPH</jats:styled-content>3, Man2α1, and Man<jats:styled-content style="fixed-case">IIX</jats:styled-content>. The Golgi trafficking protein <jats:styled-content style="fixed-case">TMED</jats:styled-content>7/p27 via small 50‐nm vesicles emanating from the Golgi cisternae was proposed to transport <jats:styled-content style="fixed-case">GLUT</jats:styled-content>‐3 to the plasma membrane for <jats:styled-content style="fixed-case">ATP</jats:styled-content> production related to sperm motility. The internal membranes revealed abundant proteins not only of Golgi cisternae, but also of endoplasmic reticulum and endosomes. <jats:styled-content style="fixed-case">COPI</jats:styled-content> and <jats:styled-content style="fixed-case">COPII</jats:styled-content> coats, clathrin, <jats:styled-content style="fixed-case">SNARE</jats:styled-content>s, annexins, atlastins, and <jats:styled-content style="fixed-case">GTP</jats:styled-content>ases were identified for vesicular trafficking and membrane fusion, in addition to ribosomes, stress proteins for protection, proteasome proteins involved in degradation, and cytoskeletal elements for migration of the <jats:styled-content style="fixed-case">HB</jats:styled-content> along the flagellum. The biogenesis of the <jats:styled-content style="fixed-case">HB</jats:styled-content> occurring at step 19 spermatids of the testis just prior to their release was uncovered as a key step in germ cell differentiation, where several proteins were expressed, some for the first time.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>As epididymal spermatozoa undergo remodeling of their protein makeup through selective degradation of sperm proteins during epididymal transit, then remodeling as a consequence of new protein synthesis is not excluded by our observations.</jats:p></jats:sec>