In vertebrates, sex steroids play crucial roles in multiple systems related to reproduction. In females, estrogens and their receptor estrogen receptor (ER or Esr) play indispensable roles in the negative sex steroid feedback regulation of pituitary gonadotropin secretion, which prevents excessive development of ovarian follicles. However, the mechanism of this feedback regulation of a gonadotropin, follicle stimulating hormone (FSH), which is essential for folliculogenesis throughout vertebrates, is poorly understood. In the present study, we generated knockouts of all subtypes of nuclear estrogen receptors in a model teleost medaka, which is suitable for the study of endocrine control and behavioral assays, and analyzed fertility, behavior and functionality of estrogen feedback in each knockout line. Among the estrogen receptors, we revealed that an estrogen receptor Esr2a plays an essential role in this feedback regulation. In addition to this, we also found that
esr2a
−/−
females showed oviduct atresia, which causes complete infertility. Interestingly,
esr2a
−/−
females showed apparently normal sexual behavior but without oviposition in response to male courtship. This phenotype indicates that physical readiness and motivation of sexual behavior is independently controlled.
Behavioral analysis plays an important role in wide variety of biological studies, but behavioral recordings often tend to be laborious and are associated with inevitable human-errors. It also takes much time to perform manual behavioral analyses while replaying the videos. On the other hand, presently available automated recording/analysis systems are often specialized for certain types of behavior of specific animals. Here, we established an open-source behavioral recording system using Raspberry Pi, which automatically performs video-recording and systematic file-sorting, and the behavioral recording can be performed more efficiently, without unintentional human operational errors. We also developed an Excel macro that enables us to easily perform behavioral annotation with simple manipulation. Thus, we succeeded in developing an analysis suite that mitigates human tasks and thus reduces human errors. By using this suite, we analyzed the sexual behavior of a laboratory and a wild medaka strain and found a difference in sexual motivation presumably resulting from domestication.
Testicular morphogenesis and functions are considered to be under the control of neural and endocrine systems. However, the available literature is mainly limited to mammals, and it remains unclear how they are regulated in teleost species. Here, we demonstrated that neuropeptide FF (NPFF) in the brain is responsible for the follicle-stimulating hormone expression in the pituitary, which facilitates the testicular morphogenesis and androgen synthesis, and subsequently contributes to successful spermatogenesis. The present findings give us important insights into the neuroendocrine regulatory mechanisms underlying the testicular morphogenesis and functions in teleosts.
Expression patterns of paralogous genes in the functionally homologous cells sometimes show differences across species. However, no reasonable explanation for the mechanism underlying such phenomena has been discovered. To understand this mechanism, the present study focused on the hypophysiotropic GnRH neurons in vertebrates as a model. These neurons express eithergnrh1orgnrh3paralogs depending on species, and apparent switching of the expressed paralogs in them occurred at least four times in vertebrate evolution. First, we found redundant expressions ofgnrh1andgnrh3in a single neuron in piranha and hypothesized that this situation may indicate an ancestral condition. We tested this hypothesis by examining the activity of piranhagnrh1/gnrh3enhancers in zebrafish and medaka, in which the twognrhparalogs are not co-expressed. Here, thegnrh1/gnrh3enhancer of piranha induced reporter RFP/GFP co-expressions in a single hypophysiotropic GnRH neuron in both zebrafish and medaka. From these results, we propose that long-lasting (~550 My) redundancy aftergnrh1/3duplication in 1R/2R WGD may be the key to apparent switching of the paralog usage among the present-day species. Moreover, interspecies analyses of enhancers indicated that the loss of enhancers rather than changes in trans-regulatory elements drove the role-division of these paralogs.
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