Cell Fate
In the Wold group we are interested in the problem of how mammalian
cell fates are specified and executed. A major challenge is to
understand at molecular and cellular levels the series of developmental
decisions that lead from multipotential, precursor cells to their
specialized, differentiated products. We use the mouse as our
primary experimental animal and the specific lineages we study
are mesodermal; they ultimately produce skeletal muscle, cardiac
muscle, and several non-muscle somitic derivatives. Skeletal
myogenesis is governed by both positive- and negative-acting regulatory
factors. In this process, coordination of cell cycle regulation
with regulation of differentiation is a hallmark of the system.
A family of four closely related, positive-acting transcription
factors appear central to muscle development. They are MyoD, myogenin, myf-5 and
MRF4/herculin. Upon transfection into many
types of non-muscle cells, each of these has the capacity to drive
recipient cells into and through the myogenic pathway. Such transformants,
under appropriate culture conditions, differentiate into skeletal myocyte-like cells that express a complex battery of muscle-specific
proteins. Given their extraordinary power to drive or even redirect
a cell fate decision, one experimental goal is to understand how
MyoD family regulators function. Projects byXin Yu, Ardem Patapoutian,
Jeong Yoon, Roger Wagner, and Dee Cornelison focus on different
aspects of this problem, emphasizing new approaches to study their
activities in in vivo settings. At the level of the whole
organism, this includes gene disruption and gene transplacement
by targeted homologous recombination to study the phenotypes of
null mutations in muscle regulators, controlled ectopic expression
in transgenic animals, the development and characterization of
cell cultures and lines from early embryonic muscle precursors,
and experiments to trace the fates of cells that have at an earlier
time in development expressed key regulators. At the molecular
level, this involves application of a novel strategy for probing
the MyoD regulatory network (forced dimer polyproteins), and further
development and application of in vivo footprinting to
help understand how protein:DNA complex formation is regulated
and related to gene activity in the cell.
Negative-acting regulators of
muscle differentiation.
At the cellular and molecular levels, it is clear that negative
regulators of skeletal myogenesis are probably just as important
in properly regulating the outcome as are the positive MyoD and
MEF2 family regulators. The interaction between the two sets
of regulators is of particular interest to us. Negative regulators
of skeletal muscle differentiation that we find especially interesting
and relevant are those that are expressed in multipotential mesodermal
precursors or in proliferating muscle precursors (myoblasts),
and it is postulated that some of these are important for specifying
their precursor status and for maintaining precursor cells in
an undifferentiated state. Others also appear to have a role
in driving proliferation of the precursor compartments at the
same time that they mitigate against execution of the muscle differentiation
program. Regulators in these classes include twist, myc, Max/myn,
Id, c-jun, and protein kinase C. Sonya Zabludoff Palmer, Kyuson Yun, and Marie Csete are studying different aspects of this problem.
Cell cycle progression and its
roles in development
A major problem in development is controlling cell proliferation
and coordinating it with cell fate decisions so that the proper
number of cells of each type are ultimately provided. Moreover,
in many cell types the function of the final differentiated cell
depends on its cell-cycle status. For skeletal muscle, differentiation
is tightly linked with entry into a G0-arrested
state. Work by Sonya Zabludoff, Marie Csete and Susan Wang is
directed at understanding regulation and execution of the entry
into the G0 state
and the role, played by that c-myc, G1 cyclins, their cogante cdks, and their recently discovered inhibitory proteins play in
directing or inhibitine that progression. A new and related thrust
is our interest in myogenic satellite cells and understanding
their lineal origin, cell cycle regulation and regulation of their
myogenic status. Dawn Cornelison and Inna Gitelman are studying
the functions and expression of cdk/cyclin inhibitory proteins
in the context of mouse development, including p16/MTS1, p15/MTS2,
p27/KIP1, p57 and p21.
This is the inevitable question when an set of regulators is
discovered. In this case, the specific problem is to learn what
turns on and then maintains expression of MyoD family members
during development. Jeong Yoon is studying this problem with
special attention to MRF4 and myf5. Studies of other regulators
that appear important in the mesodermal lineages prior to expression
of MyoD family members or in non-myotomal portions of somites
focus on mouse twist, previously cloned and characterized
in the laboratory. Kyuson Yun and Shuling Wang have looked at
different aspects of its activity.
Search: [ current | former scholar ] [ current | awarded institution ] [ quick search ]
