Sex determination strategies in 2012: towards a common regulatory model?

Sex is believed to be a complex regulatory model which involves the fine-tuned action of numerous genes affecting most aspects of an organism's functional systems. Rather than simply providing a solution in a species' need for reproductive survival, sex has been shown to be a much more intriguing phenomenon, directly controlling major morphological and physiological processes, such as development, differentiation and metabolism. This reality has also lead to the adaptation of the term "sexual dimorphism" in species with a male-female sex pattern, in order to describe the complete set of structural and functional changes involved in the establishment of the sexual phenotype. Indeed, the ability to develop and maintain what science currently perceives as "normal" sex basically implies a co-operation of various genes whose expression is induced or inhibited at preset crucial time periods by a combination of genetic and epigenetic control elements [1]. These elements may themselves be the direct target of hormonal (e.g. sex steroid) action or, alternatively, they might be affected by various mediators within the cellular microenvironment, which, depending on the species, reflect different environmental adaptations (e.g. temperature, nutrients) [2]. The temporal regulation of sexual phenotype is by itself a hot research field, since sex-related changes have been shown to pursuit not only during fetal development or early childhood, but virtually throughout life, including adult years and, eventually, reproductive senescence [3].Since the evolution of such a complex regulatory system would require significant energy resources (to cover the production of the various mediators and modulators of gene action and their distribution in the different tissues and organs) one might assume a need for a justification for its evolutionary maintenance within the global context of cellular economy. Indeed, it is likely that sex has developed in the course of evolutionary history as a m