Haploinsufficiency of SIX3 Abolishes Male Reproductive Behavior Through Disrupted Olfactory Development, and Impairs Female Fertility Through Disrupted GnRH Neuron Migration
Mating behavior in males and females is dependent on olfactory cues processed through both the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). Signaling through the MOE is critical for the initiation of male mating behavior, and the loss of MOE signaling severely compromises this comportment. Here, we demonstrate that dosage of the homeodomain gene Six3 affects the degree of development of MOE but not the VNO. Anomalous MOE development in Six3 heterozygote mice leads to hyposmia, specifically disrupting male mounting behavior by impairing detection of volatile female estrus pheromones. Six3 is highly expressed in the MOE, main olfactory bulb (MOB), and hypothalamus; all regions essential in the proper migration of the gonadotropin-releasing hormone (GnRH) neurons, a key reproductive neuronal population that migrates along olfactory axons from the developing nose into the brain. Interestingly, we find that the reduction in Six3 expression in Six3 heterozygote mice compromises development of the MOE and MOB, resulting in mis-migration of GnRH neurons due to improper olfactory axon targeting. This reduction in the hypothalamic GnRH neuron population, by 45% in adulthood, leads to female subfertility, but does not impact male hormone levels, suggesting that male infertility is not related to GnRH neuron numbers, but exclusively linked to abnormal olfaction. We here determine that Six3 is haploinsufficient for MOE development, GnRH neuron migration, and fertility, and represents a novel candidate gene for Kallmann syndrome, a form of inherited infertility.
KeywordsKallmann syndrome GnRH neuron migration Olfactory development Anosmia Reproductive behavior
The authors thank Lauren D. Sitts and Jason D. Meadows for technical assistance on this project. This work was supported by National Institutes of Health grants R01 HD082567 and R01 HD072754 (to P.L.M.) and by National Institute of Child Health and Human Development/National Institutes of Health P50 HD012303 as part of the National Centers for Translational Research in Reproduction and Infertility (P.L.M.). P.L.M. was partially supported by P30 DK063491, P42 ES101337, and P30 CA023100. E.C.P. was partially supported by National Institutes of Health R25 GM083275 and National Institutes of Health F31 HD098652. H.M.H. was partially supported by K99 HD084759. E.L.S. was partially supported by T32 HD007203, The Lalor Foundation, P42 ES101337, and T32 DK007044.
E.C.P., H.M.H., E.L.S., M.R.G. and P.L.M. designed the experiments; E.C.P., H.M.H., and E.L.S performed the experiments; E.C.P., H.M.H., E.L.S., and P.L.M. analyzed the data; E.C.P., H.M.H., E.L.S., M.R.G., and P.L.M. discussed the results; and E.C.P., H.M.H., E.L.S., M.R.G., and P.L.M. wrote the manuscript.
Compliance with Ethical Standards
All animal procedures were performed in accordance with the UCSD Institutional Animal Care and Use Committee regulations.
Conflict of Interest
The authors declare that they have no conflict of interest.
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