The Homeodomain Transcription Factors Vax1 and Six6 Are Required for SCN Development and Function


The brain’s primary circadian pacemaker, the suprachiasmatic nucleus (SCN), is required to translate day-length and circadian rhythms into neuronal, hormonal, and behavioral rhythms. Here, we identify the homeodomain transcription factor ventral anterior homeobox 1 (Vax1) as required for SCN development, vasoactive intestinal peptide expression, and SCN output. Previous work has shown that VAX1 is required for gonadotropin-releasing hormone (GnRH/LHRH) neuron development, a neuronal population controlling reproductive status. Surprisingly, the ectopic expression of a Gnrh-Cre allele (Gnrhcre) in the SCN confirmed the requirement of both VAX1 (Vax1flox/flox:Gnrhcre, Vax1Gnrh-cre) and sine oculis homeobox protein 6 (Six6flox/flox:Gnrhcre, Six6Gnrh-cre) in SCN function in adulthood. To dissociate the role of Vax1 and Six6 in GnRH neuron and SCN function, we used another Gnrh-cre allele that targets GnRH neurons, but not the SCN (Lhrhcre). Both Six6Lhrh-cre and Vax1Lhrh-cre were infertile, and in contrast to Vax1Gnrh-cre and Six6Gnrh-cre mice, Six6Lhrh-cre and Vax1Lhrh-cre had normal circadian behavior. Unexpectedly, ~ 1/4 of the Six6Gnrh-cre mice were unable to entrain to light, showing that ectopic expression of Gnrhcre impaired function of the retino-hypothalamic tract that relays light information to the brain. This study identifies VAX1, and confirms SIX6, as transcription factors required for SCN development and function and demonstrates the importance of understanding how ectopic CRE expression can impact the results.

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We thank Dr. Catherine Dulac (Harvard University, Cambridge, MA, USA) for the Lhrh-cre mice and Dr. Andrew Wolfe (Johns Hopkins University) for the Gnrh-cre mice. The Vip-luciferase plasmid was kindly provided by Dr. Satchidananda Panda (Salk Institute, La Jolla, CA, USA).


This work was supported by National Institutes of Health (NIH) Grants R01 HD072754 and R01 HD082567 (to P.L.M.). It was also supported by NIH/Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) P50 HD012303 as part of the National Centers for Translational Research in Reproduction and Infertility (P.L.M.). P.L.M. was also partially supported by P30 DK063491, P30 CA023100, and P42 ES010337. H.M.H. was partially supported by K99/R00 HD084759 and the United States Department of Agriculture National Institute of Food and Agriculture Hatch project 1018024. E.C.P. was partially supported by NIH R25 GM083275 and F31 HD098652. T.T. was partially supported by the Endocrine Society and R.H. was partially supported by the Howell Foundation and the Frontiers of Innovation Scholars Program, UC San Diego. J.A.B. was partially supported by the Frontiers of Innovation Scholars Program, UC San Diego. Work in the M.R.G. laboratory was supported by Office of Naval Research #N00014-13-1-0285, and work in the D.S.K. laboratory is supported by NIH/National Eye Institute award R01EY027011, RPB Special Scholar Award, Atkinson laboratory funds as well as by RPB Unrestricted Grant to Shiley Eye Institute and by the UCSD VisionResearch Center Core Grant P30EY022589. K.B. was supported by NIH/National Institute of Neurological Disorders and Stroke IRP funds. The University of Virginia, Center for Research in Reproduction, Ligand Assay and Analysis Core, is supported by the NIH/NICHD Grant P50 HD028934. We thank Karen J. Tonsfeldt, Erica L. Schoeller, Alexandra Yaw, Sabrina Baretto, Ichiko Saotome, and Jason D. Meadows for assistance

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Pandolfi, E.C., Breuer, J.A., Nguyen Huu, V.A. et al. The Homeodomain Transcription Factors Vax1 and Six6 Are Required for SCN Development and Function. Mol Neurobiol 57, 1217–1232 (2020).

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  • Suprachiasmatic nucleus
  • Gonadotropin-releasing hormone neuron
  • Ventral anterior homeobox 1
  • Sine oculis homeobox protein 6
  • Circadian rhythm
  • Mouse model validation