[Blueboard] Biology Research Colloquium

Crisanto M. Lopez cmlopez at ateneo.edu
Mon Oct 17 09:42:45 PHT 2016


The Department of Biology would like to invite everyone to a Research
Colloquium to be conducted by professors from the Nara Institute of Science
and Technology (NAIST, Japan). The colloquium will be held on *Friday
(October 21) in Ching Tan Room (SOM 111) from 5:00-6:30 pm.* The abstracts
of the speakers are found below. Hope to see you there.

*1. MOLECULAR MECHANISM FOR AXON GUIDANCE AND *

*NEURONAL NETWORK FORMATION*

*by Prof. Naoyuki Inagaki*

*Graduate School of Biological Science, NAIST*


         Neurons extend a long process, axons, to the right destinations
and form complicated networks in the brain; all our brain activities depend
on the neuronal network. Axonal outgrowth can be navigated by extracellular
chemical cues such as soluble chemicals (chemotaxis) and substrate–bound
chemicals (haptotaxis); they are called axon guidance molecules. Actin
filaments (F-actins) polymerize at the leading edge of axon (growth cone)
and depolymerize proximally; this, with myosin II activity, induces
retrograde flow of F-actins. It has been proposed that the forces
underlying axon outgrowth and guidance may be regulated by the modulation
of coupling efficiency between F-actin flow and the extracellular substrate
via linker “clutch” molecules. However, how cell signaling controls the
coupling efficiency remains unknown.

 We recently identified a protein shootin1, and are analyzing the molecular
mechanisms for axon outgrowth and guidance, using fluorescent live-cell
imaging, traction force microscopy and molecular loss-of-function
manipulation. We show that shootin1 and F-actin binding protein cortactin
function as clutch molecules that couples F-actin retrograde flow and the
substrate at axonal growth cones to promote axon outgrowth.

         A soluble axon guidance molecule netrin-1 positively regulates
forces at axonal growth cones via Pak1-mediated shootin1 phosphorylation.
This phosphorylation enhanced the interaction between shootin1 and F-actin
retrograde flow through cortactin and the interaction between shootin1 and
a cell adhesion molecule L1-CAM, thereby promoting force generation and
axon outgrowth. These results suggest that shootin1 is located at a
critical interface, transducing a signal of netrin-1 into the forces for
axonal haptotaxis.

         We also show that the molecular machinery composed of polymerizing
F-actins, L1-CAM, and clutch molecules shootin1 and cortactin is involved
in axonal haptotaxis directed by substrate–bound chemical cue laminin. In
this system, differential grip and slip between L1-CAM and adhesive
substrates generates directional force for the haptotaxis. In contrast to
the classical model for haptotaxis, this mechanism does not depend on cell
signaling: L1-CAM acts as both chemo-sensor and mechano-effector for
navigation.

*2. ORIGIN AND EVOLUTION OF XYLEM IN LAND PLANTS*
*by Prof. Taku Demura*
*Graduate School of Biological Science, NAIST*

Xylem is a tissue of vascular plants for conduction of water and solutes
and for supporting plant bodies, which, as wood in trees, has long been
used for natural materials including pulp, timber, and wood products.
Recent considerable effort has identified the regulatory genes for the
differentiation of xylem cells. Using Arabidopsis, we showed that
*VASCULAR-RELATED
NAC-DOMAIN6* (*AtVND6*) and *AtVND7*, encoding plant specific NAC
transcription factors, are the transcriptional switches for
water-conducting vessel cells. Further researches revealed that two genes (
*AtNST1* and *AtNST3*/*SND1*) belonging to the same gene family of *AtVND6*
and *AtVND7* are the key regulators of differentiation of fiber cells for
supporting plant bodies in Arabidopsis. Based on the phylogenetic analysis,
we also showed that 16 poplar genes (*PtVNS1* to *PtVNS16*) were homologous
to the *VND*/*NST*/*SND* genes, suggesting the functional conservation of
the gene family in vascular plants. These transcriptional switches seem to
be conserved even in evolutionary history. We also revealed that the
differentiation of water-conducting and supporting cells in moss
*Physcomitrella
patens*, hydroid and stereid cells, respectively, is regulated by genes (
*PpVNS1* to *PpVNS8*) homologous to the *VND*/*NST*/*SND* genes.
Concomitant loss of function of *PpVNS1*, *6*, and *7* and loss of *PpVNS4*
function failed to form normal hydroid and stereid cells, suggesting that,
in the early plant lineage, ancestors of *VND*/*NST*/*SND* genes may
contribute to the evolution of water-conducting and supporting cells, which
in turn could be the origin of xylem in land plants.


*Dr. rer. nat. Crisanto M. Lopez*
*Assistant Professor*
Chairperson
Department of Biology
School of Science and Engineering
Ateneo de Manila University
Katipunan Avenue, Loyola Heights,
1108 Quezon City, Philipines

*E-mail: *cmlopez at ateneo.edu
*Tel. no.:* +63-2-4266001 loc. 5610
*Telefax*: +63-2-4261034
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