regeneration, skeletal morphogenesis, cell-cell communication, extracellular matrix, hyaluronic acid, semaphorins, developmental biology, genetics
My lab is interested how the bones of the skeleton achieve the correct size. To examine this problem we study regeneration of the zebrafish fin skeleton. Fins grow by the addition of new bony fin ray segments to the distal ends of the fin rays, and fin length is regulated by mechanisms controlling both the number and length of those segments. Therefore, the segment represents the unit of bone growth in the fin.
Identification of the mutations causing phenotypes affecting segment length will reveal genetic and molecular pathways underlying segment growth. For example, we showed that mutations in the gap junction gene connexin43 cause the short fin phenotypes of reduced fin length, reduced segment length, and reduced cell proliferation. Our research suggests that Cx43 activity coordinates skeletal growth (i.e. cell proliferation) and patterning (i.e. joint formation).
The goal of my lab is to reveal how defects in Cx43-based gap junctional intercellular communication mediate skeletal morphogenesis. Using a microarray, we identified and validated several genes whose expression appears to depend on the level of Cx43 activity. We are finding that Cx43 function seems to regulate the expression of genes that function in, or modify, the extracellular environment. Thus, we identified the secreted growth factor, Sema3d, as mediating independent intercellular signaling pathways that control cell proliferation and joint formation (Ton and Iovine, 2012). We also find that the hyaluronan-based extracellular matrix contributes to these pathways (Govindan and Iovine, 2014). Most recently, we showed that the collagen-based actinotrichia are necessary for normal levels of cell proliferation and for normal placement of joints (Bhadra and Iovine, 2015). Because of the location of actinotrichia between the compartment of dividing cells and the compartment of cells that differentiate into bone and joint forming cells, we suggest that the integrity of actinotrichia signals to both compartments to coordinate growth and patterning. We are in the process of validating additional genes, and we continue to build a Cx43-dependent network in order to provide new insights into the pathways that can be regulated by gap junctional communication.
Barton, R., Khakbaz, P., Bera, I. Klauda, J.B., Iovine, M.K., Berger, B.W. 2016 Interplay of Specific Trans- and Juxtamembrane Interfaces in Plexin A3 Dimerization and Signal Transduction. Biochemistry 55: 4928-4938. doi: 10.1021/acs.biochem.6b00517
Misu, A., Yamanaka, H. Aramaki, T., Kondo, S., Skerrett, I.M., Iovine, M.K., Watanabe, M. 2016. Two Different Functions of Connexin43 Confer Two Different Bone Phenotypes in Zebrafish. J. of Biological Chemistry. 291: 24, 12601-12611. doi: 10.1074/jbc.M116.720110
Govindan, J., Tun, KM., Iovine, M.K. Cx43-Dependent Skeletal Phenotypes Are Mediated by Interactions between the Hapln1a-ECM and Sema3d during Fin Regeneration. 2016. PLoS ONE 11(2):
Bhadra, J, Banerji, R., Singh, J., Sallada, N., Eble, D.M., and Iovine, M.K. The zebrafish fibroblast cell line AB9 as a tool to complement gene regulation studies. Musculoskeletal Research. doi:10.14800/mr.992. 2015.
Barton, R., Driscoll, A., Flores, S., Mudbhari, D., Collins, T., Iovine, MK, Berger, B.W., Cysteines in the neuropilin-2 MAM domain modulate receptor homooligomerization and signal transduction. Biopolymers. doi: 10.1002/bip.22619. 2015.
Barton, R., Palacio, D., Iovine, M. K., Berger, B.W., A Cytosolic Juxtamembrane Interface Regulates Plexin A3 Oligomerization and Signal Transduction. PLoS One. doi: 10.1371/journal.pone.0116368. 2015.
Gerhardt, S.V., Jefferis, R., and Iovine, M.K., Cx40.8, a Cx43-like protein, forms gap junction channels inefficiently and may require Cx43 for its association at the plasma membrane. FEBS Letters. 583: 3419-3424. 2009.
Brown, A.M., Fisher, S., and Iovine, M.K., Osteoblast maturation occurs in overlapping proximal-distal compartments during fin regeneration in zebrafish. Dev. Dyn. 238: 2922-2928. 2009.
Hoptak-Solga, A.D., Nielsen, S., Jain, I., Thummel, R., Hyde D., and Iovine, M.K. Connexin43 is required in the population of dividing cells during fin regeneration. /Dev. Biol./ *317:* 541-548. 2008.
Iovine, M.K., Gumpert, A. Falk, M., Mendelson, T.C. Cx23, a connexin with only four extracellular-loop cysteines, forms functional gap junction channels and hemichannels. FEBS Letters. 582: 165-170. 2008.
Hoptak-Solga, A.D., Klein, K.A., DeRosa, A.M. White, T.W., and Iovine, M.K. Zebrafish short fin mutations in connexin43 lead to aberrant gap junctional intercellular communication. FEBS Letters. 581: 3297-3302. 2007.
Jain, I., Stroka, C., Yan, J., Huang, W.M., and Iovine, M.K. Bone growth in zebrafish fins occurs via multiple pulses of cell proliferation. Dev. Dyn. 236: 2668-2674. 2007.
Eastman, S.D., Chen, T.H., Falk, M.M., Mendelson, T.C., and Iovine, M.K. Phylogenetic analysis of three complete gap junction gene families reveals lineage-specific duplications and highly supported gene classes. Genomics. 87: 265-274. 2006.
Current Lab Members
Past Lab Members
2015 - from left to right: Harneel Riar, Rebecca Bowman, Joyita Bhadra, Jayalakshmi Govindan, M. Kathryn Iovine, Ph.D., Rajeswari Banerji
- Joyita Bhadra, Ph.D. - post-doctoral fellow at the Indian Institute of Science, Bangalore
- Jayalakshmi Govindan, Ph.D. - research associate at Princeton University
- Angela Hoptak, Ph.D. - instructor at Kutztown University
- Quynh Ton, Ph.D. - post-doctoral fellow at the University of Children's Hospital, Cincinnati
- Knockdown of Esco2 causes short fin ray segments (left) compared with control fin ray segments.
- Zebrafish Cx43-EGFP expression in HeLa cells (tubulin is shown in red).
- Expression of evx1 in joint-forming cells (purple) in a regenerating fin ray.
- Change in Cx40.8 localization from the plasma membrane during ontogenetic fin growth (A) to the Golgi apparatus (B) during regeneration.
- Interzone-like organization of joint-forming cells in a presumptive joint during fin regeneration.
- Expression of Col2 (green) and Hsp47 (red) in the regenerating fin. A longitudinal section (top) and a transverse section (bottom) are shown. Nuclei are stained in blue.
- Adult lof/+ fish.
- ZNS5 staining detects both bone-forming cells and joint-forming cells (green). Inset shows a longitudinal cross-section stained for both ZNS5 (green) and Cx43 (red). The staining overlaps in the joint-forming cells (arrowheads).
- Caudal fin stained with calcein to detect calcified bone matrix.