Application of comparative genomics in fish endocrinology

Abstract This review discusses the ways in which comparative genomics can contribute to the study of fish endocrinology. First, the phylogenetic position of fish and an overview of their specific endocrine systems are presented. The emphasis will be on teleosts because they are the most abundant fishes and because most data are available for this group. Second, the complexity of fish genomics is reviewed. With the vast array of genome sizes and pioidy levels, assignment of gene orthology is more difficult in fish, but this is an absolute prerequisite in functional analysis and it is important to be aware of such genome plasticity when cloning genes. The ease with which a gene is cloned at the genomic level is directly related to genome size and complexity, a factor that is not known in the majority of fish species. Finally, the methodology is presented along with specific examples of parathyroid hormone-related protein (PTHrP) (a previously unidentified hormone in fish), calcium-sensing receptor, and calcitonin (with a duplication of this particular ligand in Fugu rubripes ). Preliminary data also suggest that there are further duplicated genes in the calcium regulatory system. Comparative genomics has provided a valuable approach for isolating and characterizing a range of fish genes involved in calcium regulation. However, for understanding the physiology and endocrine regulation of this system, particularly with regard to gene duplication, an alternative approach is required in which conventional endocrinology techniques will play a significant role.