Estrogen-dependent, extrahepatic synthesis of vitellogenin in male vertebrates: A mini-review

In the last years, the hormonal balance is threatened by the interferences of substances with hormone-like action (endocrine disruptor chemicals, EDCs) that may harm animal reproduction. Most EDCs are resistant to environmental degradation and are considered ubiquitous contaminants. EDCs may have synthetic or natural origins. Pesticides used in intensive agriculture contain large amounts of chemicals with estrogenic properties, such as the alkylphenol nonylphenol (NP). Besides, animal feeding operations are important sources of natural estrogen metabolites introduced into the environment through manure application in organic farming. In both cases, EDCs can reach animals, including humans particularly at risk due to their position in the food chain. This is the reason for which it is important to use terrestrial vertebrates as sentinels in soil biomonitoring programmes. Today, the most validated biomarker of estrogenic exposure is the expression in male liver of the vitellogenin (VTG), an estrogen-dependent glycolipophosphoprotein naturally expressed only in the liver of oviparous females during the reproductive season. This report summarizes the data available on the EDC-dependent expression and the synthesis of VTG in male vertebrates, highlighting our latest studies that demonstrate the ability of testis and epididymis of the lacertid Podarcis sicula to synthesize VTG following estrogenic exposure. These findings provide, for the first time, evidence on an extrahepatic expression and synthesis of VTG in a terrestrial vertebrate and lay the groundwork for a new value of the VTG as a biomarker of environmental contamination. In addition, the results open a new scenario on the role of VTG in cells other than oocytes.