Research Departments & Organizations
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.
Dual sensing of Physiologic pH and Calcium by EFCAB9 Regulates Sperm Motility
Hwang JY, Mannowetz N, Zhang Y, Everley RA, Gygi SP, Bewersdorf J, Lishko PV, Chung JJ. Cell 2019, doi: 10.1016/j.cell.2019.03.047. 2019
Sex at Atomic Resolution.
Hwang JY, Chung JJ. Sex at Atomic Resolution. Cell 2017, 169:1174-1176. 2017
CatSperζ regulates the structural continuity of sperm Ca2+ signaling domains and is required for normal fertility.
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, 6. 2017
Chung JJ. Sugar-coated sperm. Molecular Reproduction And Development 2016, 83:859. 2016
Sperm flagellar Ca2+ signaling domains
Chung, J.J. (2016) Sperm flagellar Ca2+ signaling domains. Mol Reprod Dev. doi: 10.1002/mrd.22628. 2016
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. 2015
Structurally distinct Ca(2+) signaling domains of sperm flagella orchestrate tyrosine phosphorylation and motility.
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, 157:808-22. 2014
The control of male fertility by spermatozoan ion channels.
Lishko PV, Kirichok Y, Ren D, Navarro B, Chung JJ, Clapham DE. The control of male fertility by spermatozoan ion channels. Annual Review Of Physiology 2012, 74:453-75. 2012
A novel gene required for male fertility and functional CATSPER channel formation in spermatozoa.
Chung JJ, Navarro B, Krapivinsky G, Krapivinsky L, Clapham DE. A novel gene required for male fertility and functional CATSPER channel formation in spermatozoa. Nature Communications 2011, 2:153. 2011
PI3K/Akt signalling-mediated protein surface expression sensed by 14-3-3 interacting motif.
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. The FEBS Journal 2009, 276:5547-58. 2009
Ion channels that control fertility in mammalian spermatozoa.
Navarro B, Kirichok Y, Chung JJ, Clapham DE. Ion channels that control fertility in mammalian spermatozoa. The International Journal Of Developmental Biology 2008, 52:607-13. 2008
Biochemical characterization of the native Kv2.1 potassium channel.
Chung JJ, Li M. Biochemical characterization of the native Kv2.1 potassium channel. The FEBS Journal 2005, 272:3743-55. 2005
Genome-wide analyses of carboxyl-terminal sequences.
Chung JJ, Yang H, Li M. Genome-wide analyses of carboxyl-terminal sequences. Molecular & Cellular Proteomics : MCP 2003, 2:173-81. 2003
Functional diversity of protein C-termini: more than zipcoding?
Chung JJ, Shikano S, Hanyu Y, Li M. Functional diversity of protein C-termini: more than zipcoding? Trends In Cell Biology 2002, 12:146-50. 2002
A functional retinoic acid response element (RARE) is present within the distal promoter of the rat gonadotropin-releasing hormone (GnRH) gene.
Cho S, Chung JJ, Choe Y, Choi HS, Han Kim D, Rhee K, Kim K. A functional retinoic acid response element (RARE) is present within the distal promoter of the rat gonadotropin-releasing hormone (GnRH) gene. Brain Research. Molecular Brain Research 2001, 87:204-13. 2001
9-cis-Retinoic acid represses transcription of the gonadotropin-releasing hormone (GnRH) gene via proximal promoter region that is distinct from all-trans-retinoic acid response element.
Cho S, Chung J, Han J, Ju Lee B, Han Kim D, Rhee K, Kim K. 9-cis-Retinoic acid represses transcription of the gonadotropin-releasing hormone (GnRH) gene via proximal promoter region that is distinct from all-trans-retinoic acid response element. Brain Research. Molecular Brain Research 2001, 87:214-22. 2001
Activation of retinoic acid receptor gamma induces proliferation of immortalized hippocampal progenitor cells.
Chung JJ, Cho S, Kwon YK, Kim DH, Kim K. Activation of retinoic acid receptor gamma induces proliferation of immortalized hippocampal progenitor cells. Brain Research. Molecular Brain Research 2000, 83:52-62. 2000
Functional impairment of lens aquaporin in two families with dominantly inherited cataracts.
Francis P, Chung JJ, Yasui M, Berry V, Moore A, Wyatt MK, Wistow G, Bhattacharya SS, Agre P. Functional impairment of lens aquaporin in two families with dominantly inherited cataracts. Human Molecular Genetics 2000, 9:2329-34. 2000