Aquaporins in the male reproductive tract and sperm: Functional implications and cryobiology

<jats:title>Contents</jats:title><jats:p>Aquaporins (<jats:styled-content style="fixed-case">AQP</jats:styled-content>s) play a vital role for the transport of water and solutes across cell membranes. Classification of these ubiquitous proteins into three categories (orthodox <jats:styled-content style="fixed-case">AQP</jats:styled-content>s, aquaglyceroporins and superaquaporins) is based on their sequence similarity and substrate selectivity. In the male reproductive tract of mammals, most <jats:styled-content style="fixed-case">AQP</jats:styled-content>s (except <jats:styled-content style="fixed-case">AQP</jats:styled-content>6 and <jats:styled-content style="fixed-case">AQP</jats:styled-content>12) are found in different organs (including testis, efferent ducts and epididymis). <jats:styled-content style="fixed-case">AQP</jats:styled-content>1 and <jats:styled-content style="fixed-case">AQP</jats:styled-content>9 are the most abundant <jats:styled-content style="fixed-case">AQP</jats:styled-content>s in the efferent ducts and epididymis and play a crucial role for the secretion/reabsorption dynamics of luminal fluid during sperm transport and maturation. <jats:styled-content style="fixed-case">AQP</jats:styled-content>3, <jats:styled-content style="fixed-case">AQP</jats:styled-content>7, <jats:styled-content style="fixed-case">AQP</jats:styled-content>8 and <jats:styled-content style="fixed-case">AQP</jats:styled-content>11 are the most abundant <jats:styled-content style="fixed-case">AQP</jats:styled-content>s in sperm and are involved in the regulation of their volume, which is required for the differentiation of spermatids into spermatozoa during spermatogenesis, as well as in sperm transit along environments of different osmolality (male and female reproductive tracts). While different studies conducted in oocytes and embryos have demonstrated that <jats:styled-content style="fixed-case">AQP</jats:styled-content>s are important for cryotolerance, data in sperm are scarce. At present, mounting evidence indicates that <jats:styled-content style="fixed-case">AQP</jats:styled-content>3, <jats:styled-content style="fixed-case">AQP</jats:styled-content>7 and <jats:styled-content style="fixed-case">AQP</jats:styled-content>11 are involved in the sperm response to variations of osmolality and to freeze‐thawing procedures. All these studies contribute to understand the physiology of both male reproductive tract and sperm, and open up new research ventures on the improvement of sperm cryopreservation protocols.</jats:p>