Fertility; Ion Channels; Reproduction; Sperm Capacitation; Sperm Motility; Signal Transduction; Membrane Microdomains
Life perpetuates through successful fertilization. We study membrane receptors, ion channels, and their downstream signaling molecules that regulate sperm motility and fertility in mammals. In particular, we study the primary calcium channel “CatSper” and its accessory subunits. Strong evolutionary pressure on reproduction have endowed sperm with highly evolved and specialized calcium signaling complexes. A long-term goal is to elucidate the unique molecular and structural adaptations in the ion channels complex that mediate successful fertilization as well as other critical, physiological events in mammalian reproduction. To this end, we use a variety of approaches including mouse genetics, biochemical studies, dynamic optical imaging of live cells, and cutting-edge super-resolution microscopy. Our research has clinical implications in the treatment of human infertility as well as contraception, and expands our understanding of calcium signaling.
Extensive Research Description
In humans, only about 200 out of 200 million spermatozoa ever reach the oviduct and of these only one spermatozoon fertilizes the egg. During the life-changing journey, sperm cells not only adapt to changes in local environments, but also respond to cues along the female reproductive tract. Ion channels and transporters enable sperm to respond to the constantly changing environment by controlling the sperm’s calcium and proton concentrations that in turn results in changes in motility. However, the molecular details are largely unknown.
A current focus of our research is to understand the mechanisms by which the sperm motility and male fertility are regulated by ion channels. In particular, we are studying the sperm-specific calcium channels “CatSpers” that are essential for sperm hyperactivation (an asymmetric flagellar motion of the sperm tail that gives spermatozoa the force to penetrate the zona pellucida of the egg.)
First, we characterized the native CatSper channel complex, identifying novel CatSper accessory subunits to better understand molecular organization of the CatSper channel and its signal transduction in mammalian fertilization. The accessory subunits are key to understand the assembly and the organization of an ion channel complex. By generating mice lacking each subunit we found that one of their function is to protect the pore-forming subunits from premature degradation, and that only the properly assembled, complete channel complex can be specifically targeted to the flagellar membrane.
Calcium signaling specificity is accomplished via the ion’s precise spatiotemporal localization in a cell. Mammalian sperm has elaborate cytoskeletal structures in the tail for motility regulation. As the sperm flagella is less than 1 um in diameter, the spatial information of the signaling molecules inside the flagella cannot be resolved by conventional light microscope due to diffraction limit of light. Thus, we have applied super-resolution stochastic optical reconstruction microscopy (STORM) to image CatSper and the potential downstream signaling molecules within the flagella. Our studies showed that the CatSper channel forms unique four linear calcium domains that organize calcium signaling proteins along the flagella, providing strong evidence for molecularly defined, structured calcium signaling domains. These domains orchestrate the timing and extent of complex phosphorylation cascade, potentially coordinating the flagellar waveform. We are currently studying the molecular mechanisms by which CatSper and calcium signaling molecules are organized in the four distinct lines.
Most importantly, we demonstrated that capacitation (a physiological process that enables spermatozoa to obtain the fertilizing ability in the female reproductive system through biochemical and functional changes) results in heterogeneous sperm populations with molecular differences in the CatSper spatial domains. These data suggest that the exceptionally few spermatozoa that reach the egg have a distinct molecular signature from those that fail in the female reproductive tract! Ongoing projects address characterization of the successful spermatozoa at the molecular levels. We are particularly interested in the molecular changes of the sperm membrane receptors and ion channels during navigation in the female reproductive tracts in situ.
Disruption of many of membrane receptors and ion channels leads to infertility in humans. The information gained from our research will improve in vitro fertilization methods and enable new contraceptive approaches. Ultimately, our research shall explain they very first life event that allows all the subsequent animal physiology.
Sex at Atomic Resolution
Hwang, J. and Chung, J.J. (2017) Sex at Atomic Resolution. Cell 169 (7): 1174-1176. http://dx.doi.org/10.1016/j.cell.2017.05.043
CatSperz Regulates the Structural Continuity of Sperm Ca2+ Signaling Domains and is Required for Normal Fertility.
Chung, J.J.*, Miki, K., Kim, D., Shim, S.H., Shi, H.F., Hwang, J.Y., Cai, X., Iseri, Y., Zhuang, X., and Clapham, D.E.* (2017) eLife 10.7554/eLife.23082
Chung, J.J. (2016) Sugarcoated sperm. Mol Reprod Dev. dos:10.1002/mrd.22732
Sperm flagellar Ca2+ signaling domains
Chung, J.J. (2016) Sperm flagellar Ca2+ signaling domains. Mol Reprod Dev. doi: 10.1002/mrd.22628.
The Concise Guide to PHARMACOLOGY 2015/16: Overview
Alexander, S.P., Kelly, E., Marrion, N., Peters, J.A., Benson, H.E., Faccenda, E., Dawson, A.J., Sharman, J.L., Southan, C., Buneman, O.P., Cattrall, W.A., Cidlowski, J.A., Davenport, A.P., Fabbro, D., Fan, G., McGrath, J.C., Spedding, M., Davies, J.A.; CGTP Collaborators. The Concise Guide to PHARMACOLOGY 2015/16: Overview. Br J Pharmacol. 2015 Dec;172(24):5729-43. doi: 10.1111/bph.13347.
Structurally distinct Ca2+ signaling domains of sperm flagella orchestrate tyrosine phosphorylation and motility
Chung, J.J.*, Shim, S.H.*, Everley, R.A. Gygi, S.P. Zhuang, X., and Clapham, D.E. (2014) Structurally distinct Ca2+ signaling domains of sperm flagella orchestrate tyrosine phosphorylation and motility. Cell 157 (4): 808-822. (*Equal contribution) (Selected for PaperFlicks; Cell video abstract online, Recommended by Faculty of 1000)
The control of male fertility by spermatozoan ion channels
Lishko, P., Kirichok, Y., Ren, D., Navarro, B., Chung, J.J., and Clapham, D.E. (2012) The control of male fertility by spermatozoan ion channels. Ann. Rev. of Physiol. 74: 453-470.
A novel gene required for male fertility and functional CATSPER channel formation in spermatozoa
Chung, J.J., Navarro, B., Krapivinsky, G., Krapivinsky, L., and Clapham, D.E. (2011) A novel gene required for male fertility and functional CATSPER channel formation in spermatozoa. Nat Commun 2: 153 doi:10.1038/ncomms1153.
PI3K/Akt signaling-mediated surface expression sensed by 14-3-3 interacting motif
Chung, J.J., Okamoto, Y., Coblitz, B., Li, M., Qiu, Y., and Shikano, S. (2009) PI3K/Akt signaling-mediated surface expression sensed by 14-3-3 interacting motif. FEBS Let. 276 (19): 5547-58.
Ion channels that control fertility in mammalian spermatozoa
Navarro, B., Kirichok, Y., Chung, J.J., and Clapham, D.E. (2008) Ion channels that control fertility in mammalian spermatozoa Int. J. Dev. Biol. 52: 607-613.
Biochemical characterization of the native Kv2.1 potassium channel.
Chung, J.J. and Li, M. (2005) Biochemical characterization of the native Kv2.1 potassium channel. FEBS J. 272 (14): 3743-55.
Genome-wide Analyses of Carboxyl-terminal Sequences
Chung, J.J., Yang, H., and Li M. (2003) Genome-wide Analyses of Carboxyl-terminal Sequences. Mol Cell Proteomics 2(3): 173-81.
Functional diversity of protein C-termini: more than zipcoding?
Chung, J.J., Shikano, S., Hanyu, Y., and Li, M. (2002) Functional diversity of protein C-termini: more than zipcoding? Trends Cell Biol. 12(3):146-50.
A functional retinoic acid response element (RARE) is present within the distal promoter of the rat gonadotropin-releasing hormone (GnRH) gene
Cho, S., Chung, J.J., Choe, Y., Choi, H.S., Kim D.H., Rhee, K., and Kim, K. (2001) A functional retinoic acid response element (RARE) is present within the distal promoter of the rat gonadotropin-releasing hormone (GnRH) gene. Brain Res Mol Brain Res. 87(2): 204-13.
9-cis-Retinoic acid represses transcription of the gonadotropin-releasing hormone (GnRH) gene via promoter region and that is distinct from all-trans-retinoic acid response element
Cho, S., Chung, J.J., Han J., Lee B.J., Kim D. H., Rhee K., and Kim K. (2001) 9-cis-Retinoic acid represses transcription of the gonadotropin-releasing hormone (GnRH) gene via promoter region and that is distinct from all-trans-retinoic acid response element. Brain Res Mol Brain Res. 87(2): 214-22.
Activation of retinoic acid receptor gamma induces proliferation of immortalized hippocampal progenitor cells
Chung, J.J., Cho, S., Kwon, Y.K., Kim, D.H., and Kim, K. (2000) Activation of retinoic acid receptor gamma induces proliferation of immortalized hippocampal progenitor cells. Brain Res Mol Brain Res. 83(1-2): 52-62.
Functional impairment of lens aquaporin in two families with dominantly inherited cataracts
Francis, P.*, Chung, J.J.*, Yasui, M., Berry, V., Moore, A., Wyatt, M.K., Wistow, G., Bhattacharya, S.S., and Agre, P. (2000) Functional impairment of lens aquaporin in two families with dominantly inherited cataracts. Hum Mol Genet. 9(15): 2329-34. (*Equal contribution)
Full List of PubMed Publications
- Hwang JY, Chung JJ: Sex at Atomic Resolution. Cell. 2017 Jun 15. PMID: 28622504
- Chung JJ, Miki K, Kim D, Shim SH, Shi HF, Hwang JY, Cai X, Iseri Y, Zhuang X, Clapham DE: CatSperζ regulates the structural continuity of sperm Ca2+ signaling domains and is required for normal fertility. Elife. 2017 Feb 23; 2017 Feb 23. PMID: 28226241
- Chung JJ: Sugar-coated sperm. Mol Reprod Dev. 2016 Oct. PMID: 27591546
- Chung JJ, Shim SH, Everley RA, Gygi SP, Zhuang X, Clapham DE: Structurally distinct Ca(2+) signaling domains of sperm flagella orchestrate tyrosine phosphorylation and motility. Cell. 2014 May 8. PMID: 24813608
- Lishko PV, Kirichok Y, Ren D, Navarro B, Chung JJ, Clapham DE: The control of male fertility by spermatozoan ion channels. Annu Rev Physiol. 2012; 2011 Oct 13. PMID: 22017176
- Chung JJ, Navarro B, Krapivinsky G, Krapivinsky L, Clapham DE: A novel gene required for male fertility and functional CATSPER channel formation in spermatozoa. Nat Commun. 2011 Jan 11. PMID: 21224844
- Chung JJ, Okamoto Y, Coblitz B, Li M, Qiu Y, Shikano S: PI3K/Akt signalling-mediated protein surface expression sensed by 14-3-3 interacting motif. FEBS J. 2009 Oct; 2009 Aug 19. PMID: 19691494
- Navarro B, Kirichok Y, Chung JJ, Clapham DE: Ion channels that control fertility in mammalian spermatozoa. Int J Dev Biol. 2008. PMID: 18649274
- Chung JJ, Li M: Biochemical characterization of the native Kv2.1 potassium channel. FEBS J. 2005 Jul. PMID: 16008572
- Chung JJ, Yang H, Li M: Genome-wide analyses of carboxyl-terminal sequences. Mol Cell Proteomics. 2003 Mar; 2003 Apr 7. PMID: 12682279
- Chung JJ, Shikano S, Hanyu Y, Li M: Functional diversity of protein C-termini: more than zipcoding? Trends Cell Biol. 2002 Mar. PMID: 11859027