Modeling the endocrine control of vitellogenin production in female rainbow trout

Abstract

The rainbow trout endocrine system is sensitive to changes in annual day length, which is likely the principal environmental cue controlling its reproductive cycle. This study focuses on the endocrine regulation of vitellogenin (Vg) protein synthesis, which is the major egg yolk precursor in this fish species. We present a model of Vg production in female rainbow trout which incorporates a biological pathway beginning with sex steroid estradiol-17β levels in the plasma and concluding with Vg secretion by the liver and sequestration in the oocytes. Numerical simulation results based on this model are compared with experimental data for estrogen receptor mRNA, Vg mRNA, and Vg in the plasma from female rainbow trout over a normal annual reproductive cycle. We also analyze the response of the model to parameter changes. The model is subsequently tested against experimental data from female trout under a compressed photoperiod regime. Comparison of numerical and experimental results suggests the possibility of a time-dependent change in oocyte Vg uptake rate. This model is part of a larger effort that is developing a mathematical description of the endocrine control of reproduction in female rainbow trout. We anticipate that these mathematical and computational models will play an important role in future regulatory toxicity assessments and in the prediction of ecological risk.

A Computational Model of the Rainbow Trout Hypothalamus-Pituitary-Ovary-Liver Axis

“…The liver plays an essential role in the reproductive process because it synthesizes the egg yolk precursor protein VTG, which is necessary for oocyte growth and development [ 39 ]. Our model for VTG synthesis is largely based on the model described by [ 12 ]. VTG synthesis is initiated when E2 binds to a nuclear estrogen receptor, R, at a binding rate of k on,ER , which is produced by transcription of the estrogen receptor mRNA, mR.…”

“…Most parameter values were estimated directly from previously published experimental studies, prior modeling efforts [ 11 , 12 ] or modified slightly from literature values. These parameters and their sources are identified in Table 2 .…”

“…kisutch ) hypothalamus-pituitary-gonad axis was described [ 11 ], which added a simple description of oocyte maturation, synthesis of DHP and separate descriptions for FSH and LH. A more detailed description of vitellogenesis throughout the reproductive cycle was described for rainbow trout [ 12 ] and included parameters for the expression of mRNA coding for the estrogen receptor and VTG. A specialized model for the unnatural stimulation of vitellogenesis in male trout was presented [ 13 ], which focused on transcriptional imprinting of VTG expression.…”

“…The objective of the present study is to present a comprehensive model for the HPOL axis for female rainbow trout that can be used to assess impacts of physical and chemical stressors on reproduction. We combine elements of past models [ 11 , 12 ] with new features that better characterize processes associated with oocyte growth and maturation.…”

The pros and cons of ecological risk assessment based on data from different levels of biological organization

“…Antczak et al 2015). Most dynamic models assume a known AOP and predict organismal endpoints of ecological importance, for example, those linking molecular mechanisms determining levels of steroid hormones or vitellogenin with well-understood connections to reproduction (Li et al 2011, Murphy et al 2005, Sundling et al 2014, Watanabe et al 2009). …”