Genomic Approaches to Study Genetic and Environmental Influences on Fish Sex Determination and Differentiation

Abstract

The embryonic gonad is the only organ that takes two mutually exclusive differentiating pathways and hence gives rise to two different adult organs: testes or ovaries. The recent application of genomic tools including microarrays, next-generation sequencing approaches, and epigenetics can significantly contribute to decipher the molecular mechanisms involved in the processes of sex determination and sex differentiation. However, in fish, these studies are complicated by the fact that these processes depend, perhaps to a larger extent when compared to other vertebrates, on the interplay of genetic and environmental influences. Here, we review the advances made so far, taking into account different experimental approaches, and illustrate some technical complications deriving from the fact that as development progresses it becomes more and more difficult to distinguish whether changes in gene expression or DNA methylation patterns are the cause or the consequence of such developmental events. Finally, we suggest some avenues for further research in both model fish species and fish species facing specific problems within an aquaculture context.

Heat-induced masculinization in domesticated zebrafish is family-specific and yields a set of different gonadal transcriptomes

“…58), earlier attempts at induced in vivo reprogramming in rodent models have resulted in the appearance of teratomas in multiple tissues (59). Our observation may be linked to the extraordinary plasticity of fish gonads compared with most other vertebrate tissues (60,61), and constitutes an aspect that deserves further study.…”

Genetic basis and biotechnological manipulation of sexual dimorphism and sex determination in fish

“…A variety of environmental factors, such as hormones, temperature, pH, density, light intensity and hypoxia, may affect sex determination pathway. Much evidence indicates that in many fish species with genetic sex determination, environmental factors such as temperature may overwhelm the effect of genetic factors at the edge of temperature tolerance threshold [91,92].…”

“…In most of fish species, no matter whether there is a sex determining gene or not, the change of sex steroid concentration or temperature is able to induce sex reversal, and thereby leads to the discordance between genetic and physiological phenotypes [44,92,93]. Temperature is the main factor affecting sex differentiation, because a lot of observations have shown in most of temperature-sensitive fishes that the male proportion increases along with elevation of hatching temperature, and low temperature is able to induce ovarian development [107109].…”

“…At juvenile stage, the ovarian structure is regressed in near half of the population and eventually develops into a normal testis [104,105]. Sex differentiation is dependent on sex determination, but the whole process of embryonic development, sex determination and differentiation is exposed to the outside environment with many variable factors, so that fish must utilize diverse types of sex determination mechanisms and plastic patterns of sex differentiation to gradually adapt to the habitat environment during the evolution [6,92,106].…”

Genetic variability and performance of Asian swamp eel Monopterus albus (Zuiew, 1793) from West Java cultured in saline water medium

“…The physiological ability of an organism in responding changes in its living environment is influenced by its genetical component (Piferrer et al, 2012). In general a population that has a higher genetic variability shows its ability to respond a better environment in its adaptation process to feed suffieciency, water quality, and disease resistance (Gjedrem, 2010).…”