Tatsuma Mohri
Current Interests
My research
interest is on the mechanisms of cellular responses induced by biological
activators, intracellular signal transduction, and expression of cellular
functions. One of my main subjects is the mechanism of egg activation at
fertilization. Changes in intracellular Ca2+ ([Ca2+]i)
including repetitive Ca2+ changes called Ca2+
oscillations are pivotal events of egg activation to investigate. I have been
studying fertilization in several species, for example, sea urchin, sand
dollar, starfish, Xenopus, ascidian, hamster and mouse. During
fertilization many events occur. A transient increase of [Ca2+]i
causes cortical granule breakdown (CGB). Intracellular pH increases and various
kinases activation, male and female pronucleus formation, aster formation, fusion
of pronuclei, and etc occur. The release of [Ca2+]i is
thought to initiate development in most organisms. Therefore it is very
important to study the mechanism of the release of [Ca2+]i
during fertilization. I have analyzed a spatiotemporal pattern in [Ca2+]i
in eggs of sea urchin, ascidian, mouse, and hamster using several kinds of
fluorescent Ca2+ probes, such as Fura-2, Indo-1, Calcium Green, and
Fluo-3. However, it is not still clear how sperm initiates the [Ca2+]i
release in eggs in detail and
how the released [Ca2+]i activates eggs afterward. In
other words, not only a signaling pathway toward the release of [Ca2+]i
and the downstream
signaling after [Ca2+]i release but also their relative roles of
intracellular and extracellular Ca2+ still remain unclear.
The other important early phenomenon of
fertilization is the depolarization of membrane potential in many species eggs.
When eggs are voltage-clamped at a certain voltage, following insemination, a
membrane current so called “the activation current” is observed in many aquatic
animals such as amphibian and echinoderm. It is also very important to
understand the interchange of ions across the cell membrane during
fertilization. Electrophysiological study leads to more precise and fruitful
information about fertilization. I have studied the mechanism of releasing [Ca2+]i
by investigating the activation current and simultaneously measuring the
release of [Ca2+]i following insemination in
voltage-clamped eggs of L. variegatus. I would like to perform
simultaneous measurements of intracellular signals including [Ca2+]i
and the activation current more precisely in other species including Japanese
sea urchins (H. pulcherrimus, S. mirabilis, S. nudus、and T. hardwickii) or other marine animal eggs and
characterize those patterns in different species from the view of comparative
physiology and evolution. The
phenomenon still strongly intrigues me.
My other current
interest is studying mitochondrial behavior and its physiological role upon
fertilization or other cellular responses induced by intracellular acting
substances such as steroid hormones or by other artificial chemicals. Recently
I have studied a signaling of nitric oxide (NO) and its role upon fertilization
in sea urchin eggs. I found a signal of NO increase had a significant role in
hardening of fertilization envelop and it was related to mitochondria. In
separate experiments, I found an interesting phenomenon that is the oscillation
of mitochondrial membrane potential in cultured human umbilical vein
endothelial cells (HUVEC) when cells are highly stained with normal
mitochondrial dye such as MitoTracker CMXR. I am presently working on 1) the
relation between intracellular [Ca2+]i and mitochondrial
activation during fertilization in sea urchin eggs and 2) the mechanism of the
mitochondrial oscillation in HUVEC.
Expertise
I was trained in
different types of light microscopy and video microscopy in laboratories of Dr.
Hiramoto and Dr. Hamaguchi in Tokyo Institute of Technology. By using Nomarski
optics and High-speed video, I have studied the behavior of cortical granule
breakdown and its rate in sea urchin eggs. I learned micromanipulation and
microinjection using constriction micropipettes according to the method of
Hiramoto (Hiramoto, Y. Exp. Cell Res. 87, 403-406, 1974). The
great advantage of this method is that any volume of fluid you want to
microinject can be done accurately. Another advantage is to determine whether
microinjection is successful or not because silicon oil is used as a cap on the
injection solution. The silicon oil is also used to keep each solution separate
in the same pipette. This constriction pipette method is also used to transplant
a cell component one cell to another cell.
I have learned Ca2+ imaging and
measurement with both a conventional fluorescent microscopy and a confocal
microscopy using animal oocytes, b-cell, and brown adipocytes. I have learned
the method to analyze fluorescence images with Fura-2, Ca-Green 1, Fluo-3,
etc., using Quantex system, Image-1 AT, FL, NIHimage, HiSCA, and AquaCosmos
(Hmamatsu Photonics Inc). I also learned intracellular pH measurements and H2O2
release measurement using Amplex Red. I also learned electrophysiology,
especially the single electrode voltage-clamp method in echinoderm eggs and
two-electrode voltage clamp method in Xenopus eggs. Now I am able to
measure simultaneously the membrane current or fertilization potential changes
and fluorescence changes induced by changes in intracellular signals such as
[Ca2+]i, NO, or intracellular pH.
Publication
1.
Mohri T., Sokabe, M., and
Kyozuka, K. (2008). Nitric oxide (NO) increase in sea urchin eggs upregulates
fertilization envelope hardening. Dev Biol 322: 251-262. http://www.ncbi.nlm.nih.gov/pubmed/18694744
2.
Mohri
T. and
Yoshida S. (2005). Estrogen and bisphenol A disrupt spontaneous [Ca2+]i
oscillations in mouse oocytes. Biochem Biophys Res Comm 326:
166-173. http://www.ncbi.nlm.nih.gov/pubmed/15567167
3.
Mohri, T., Shirakawa, H., Oda,
S., Sato, M. S., Mikoshiba, K., and
4.
Deguchi, R., Shirakawa, H., Oda, S., Mohri, T.,
and
5.
Sato, M.S., Yoshitomo, M., Mohri, T., and
6.
Oda, S., Deguchi, R., Mohri, T., Shikano,
T., Nakanishi, S., and
7.
Kyozuka, K., Deguchi, R., Mohri, T., and
8.
Mohri, T.,
9.
Mohri, T., Ivonnet, P. I., and
Chambers, E. L. (1995). Effect on sperm induced activation current and increase
of cytosolic Ca2+ of agents that modify the mobilization of [Ca2+]
10.
Mohri, T., and Hamaguchi, Y.
(1991). Measuring Ca2+ during fertilization in sea urchin eggs with
Fura-2 (in Japanese). Cell Sci. 7: 100-107.
11.
Mohri, T. and Hamaguchi, Y.
(1991). Propagation of transient Ca2+ increase in sea urchin eggs
upon fertilization and its regulation by microinjection EGTA solution. Cell
Struct. Funct. 16: 157-165. http://www.ncbi.nlm.nih.gov/pubmed/1907218
12.
Mohri, T. and Hamaguchi, Y.
(1990). Quantitative analysis of process of cortical granule breakdown in sea
urchin eggs. Cell Struct. Funct. 15: 309-315. http://www.ncbi.nlm.nih.gov/pubmed/2085846
13.
Hamaguchi, Y., Hamaguchi, M. S., and Mohri, T.
(1990). Ca2+ measurement using fluorescent indicators (in Japanese).
The Cell (Saiho) 22: 18-21.
14.
Hamaguchi, Y., Hamaguchi, M. S., and Mohri, T.
(1990). Transient Ca2+ increase during fertilization and its role in
cortical granule breakdown in sea urchin egg. In Metal Ions in Biology and
Medicine. Eds. Ph. Collery, L. A. Poirier, M. Manfait, J. C.
Etienne, John Libby Eurotext, Paris, pp 132-134.
15.
Mohri, T. and Hamaguchi, Y.
(1989). Analysis of breakdown of cortical granule in echinoderm eggs by
microinjection of second messengers. Cell Struct. Funct. 14:
429-438.
16.
17.
18.
Yamagata, Y., Mohri,
T., Yamakoshi, M., and Inomata, K. (1981). Constant AMP synthesis in
aqueous solution by electric discharges.
Origin of Life 11: 233-235.
Yamagata, Y. and Mohri,
T. (1982). Formation of cyanate and carbamyl phosphate by electric
discharges of model primitive gas. Origin of Life 12: 41-44.
Mohri, T. and Hamaguchi, Y.
(1989). Analysis of breakdown of cortical granule in echinoderm eggs by
microinjection of second messengers. Cell Struct. Funct. 14:
429-438.
Hamaguchi, Y.,
Hamaguchi, M. S., and Mohri, T. (1990). Transient Ca2+ increase
during fertilization and its role in cortical granule breakdown in sea urchin
egg. In Metal Ions in Biology and Medicine. Eds. Ph.
Collery, L. A. Poirier, M. Manfait, J. C. Etienne, John Libby Eurotext, Paris,
pp 132-134.
Hamaguchi, Y.,
Hamaguchi, M. S., and Mohri, T. (1990). Ca2+ measurement
using fluorescent indicators (in Japanese). The Cell (Saiho) 22:
18-21.
Mohri, T. and Hamaguchi, Y.
(1990). Quantitative analysis of process of cortical granule breakdown in sea
urchin eggs. Cell Struct. Funct. 15: 309-315.
Mohri, T. and Hamaguchi, Y.
(1991). Propagation of transient Ca2+ increase in sea urchin eggs
upon fertilization and its regulation by microinjection EGTA solution. Cell
Struct. Funct. 16: 157-165.
Mohri, T., and Hamaguchi, Y.
(1991). Measuring Ca2+ during fertilization in sea urchin eggs with
Fura-2 (in Japanese). Cell Sci. 7: 100-107.
Mohri, T., Ivonnet, P. I., and
Chambers, E. L. (1995). Effect on sperm induced activation current and increase
of cytosolic Ca2+ of agents that modify the mobilization of [Ca2+]i.
I. Heparin and Pentosan polysulfate Dev. Biol. 172: 139-157.
Mohri, T., Miyazaki, S.,
Shirakawa, H., and Ikegami, S. (1998). Sperm-induced local [Ca2+]i
rise separated from the Ca2+ wave in sea urchin eggs in the presence
of a gamete fusion inhibitor, jaspisin. Development 125: 293-300.
Kyozuka, K., Deguchi,
R., Mohri, T., and Miyazaki, S. (1998). Injection of sperm extract
mimics spatiotemporal dynamics of Ca2+ responses and progression of
meiosis at fertilization of ascidian oocytes. Development 125:
4099-4105.
Oda, S., Deguchi, R., Mohri,
T., Shikano, T., Nakanishi, S., and Miyazaki, S. (1999). Spatiotemporal
dynamics of the [Ca2+]i rise induced by microinjection of
sperm extract into mouse eggs: preferential induction of a Ca2+ wave
from the cortex mediated by the inositol 1,4,5-trisphosphate receptor. Dev.
Biol. 209: 172-185.
Sato, M.S., Yoshitomo,
M., Mohri, T., and Miyazaki, S. (1999). Spatiotemporal analysis of [Ca2+]i
rises in mouse eggs after intracytoplasmic sperm injection (ICSI). Cell
Calcium 26: 49-58.
Deguchi, R., Shirakawa,
H., Oda, S., Mohri, T., and Miyazaki, S. (2000). Spatiotemporal analysis
of Ca2+ waves
in relation to the sperm entry site and animal-vegetal axis during Ca2+ oscillations in fertilized mouse eggs. Dev. Biol. 218: 299-313.
Mohri, T., Shirakawa, H., Oda,
S., Sato, M. S., Mikoshiba, K., and Miyazaki, S. (2001). Analysis of Mn2+/Ca2+
influx and release during Ca2+ oscillations in mouse eggs injected
with sperm extract. Cell Calcium 29: 311-325.
Mohri T. and Yoshida S. (2005).
Estrogen and bisphenol A disrupt spontaneous [Ca2+]i oscillations
in mouse oocytes. Biochem Biophys Res Comm 326: 166-173.
1.Mohri T., Sokabe, M., and
Kyozuka, K. (2008). Nitric oxide (NO) increase in sea urchin eggs upregulates
fertilization envelope hardening. Dev Biol 322: 251-262.
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