Research Interests

When most eukaryotic cells divide, the nuclear envelope surrounding the genomic DNA is disassembled and the DNA condenses into mitotic chromosomes. After cell division, the nuclear envelope assembles around the chromosomes as they decondense to reform a nucleus. Our research examines two topics related to cell division: 1. the intracellular molecules that initiate cell division and 2. the mechanisms by which the nuclear envelope is disassembled and re-assembled each cell division. Cell-free extracts of Xenopus laevis eggs capable of cell cycle events in vitro are used for our studies.

Cell cycle control: important regulators of cell division are mitotic cyclins, proteins that increase in abundance during much of the cell cycle and are degraded rapidly as cells divide. Cyclin degradation is essential for normal cell division since mitotic arrest occurs when cyclins are not degraded appropriately. The mechanism of cyclin degradation is being investigated with the aim of characterizing the proteins involved in this process.

Nuclear envelope assembly: nuclear envelope components that are disassembled as cells divide are re-used to assemble the nuclear envelope at the end of cell division. In extracts capable of nuclear envelope assembly, two populations of vesicles have been identified as precursors of the nascent nuclear envelope. One population of vesicles binds chromosomes, whereas the other population is unable to bind chromosomes but readily fuses with the chromosome-bound vesicles. We are attempting to identify the proteins involved in chromosome binding and in vesicle-vesicle fusion and to identify the fraction containing the disassembled nuclear pore proteins.

 

Courses Taught

Selected publications

• Pati, D., M.J. Lohka and H.R. Habibi. (2000). Time-related effect of GnRH on histone H1 kinase activity in the goldfish follicle-enclosed oocyte. Can. J. Physiol. Pharmacol. 78: 107-1071.
• Tokumoto, T., M. Tokumoto, K. Seto, R. Horiguchi, Y. Nagahama, S. Yamada, K. Ishikawa and M.J. Lohka. 1999. Disappearance of a novel protein component of the 26S proteasome during Xenopus oocyte maturation. Exp. Cell Res. 247: 313-319.
• Bodoor, K., S. Shaikh, D. Salina, W.H. Raharjo, R. Bastos, M. Lohka and B. Burke. 1999. Sequential recruitment of NPC proteins to the nuclear periphery at the end of mitosis. J. Cell Sci. 112: 2253-2264.
• Bitangcol, J.C., A.S.-S. Chau, E. Stadnick, M.J. Lohka, B. Dicken and E.K. Shibuya. 1998. Activation of the p42MAPK pathway inhibits cdc2 activation and entry into M-phase in cycling Xenopus egg extracts. Mol. Biol. Cell. 9: 451-467.
•  Lohka, M.J. 1997. Analysis of nuclear envelope assembly using extracts of Xenopus eggs. Methods in Cell Biology. 53: 367-395.
• van der Velden, H.M.W. and M.J. Lohka. 1994. Cell cycle-regulated degradation of Xenopus cyclin B2 requires binding to p34^cdc2. Molec. Biol. Cell. 5: 713-724.
• van der Velden, H. M. W., and M.J. Lohka. 1993. Mitotic arrest caused by the amino-terminus of Xenopus cyclin B2. Molec. and Cell. Biol. 13: 1480-1488.
• Vigers, G. P. A. and M.J. Lohka. 1992. Regulation of nuclear envelope precursor functions during cell division. J. Cell Sci. 102: 273-284.
• Vigers, G. P. A. and M.J. Lohka. 1991. A distinct vesicle population targets membranes and pore complexes to the nuclear envelope in Xenopus eggs. J. Cell Biol. 112: 545-556.