Abstracts - Society for Developmental Biology

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differentiated cell type, which may have broad implications in the treatment of disorders associated with cell invasive
behavior.
Program/Abstract # 385
Investigating the role of lin-42, the C. elegans period homolog, in developmental timing
McCulloch, Katherine, University of Minnesota, MinneapolisUnited States; Wohlschlegel, James (Los Angeles, CA,
United States); Rougvie, Ann (Minneapolis, United States)
Precise temporal control is a critical component of developmental regulation. In humans, for example, puberty, the juvenile
to adult transition, is regulated by a highly complex combination of genetic and environmental factors. Aberrant timing of
puberty is predictive of serious health problems later in life, so understanding these processes is critical. Significant
insights into developmental timing mechanisms have been achieved through studies in C. elegans, which uncovered several
conserved temporal regulators termed heterochronic genes. These include lin-28, which has since been implicated in
timing the onset of puberty in mice and humans. In addition, study of developmental timing revealed the first miRNAs
identified: lin-4 and let-7. Let-7 miRNA is of particular interest. Its sequence is identical between C. elegans and humans,
and in both systems, let-7 activity promotes differentiation. Another highly conserved heterochronic gene is lin-42, the C.
elegans period homolog. period is a key component of the fly and vertebrate circadian clock, which synchronizes behavior
and gene expression with the 24 hour cycle. In C. elegans, however, lin-42 acts largely as a developmental timer. In lin-42
mutant animals, the larval-to-adult transition occurs too early. Although lin-42 has long been known as a key component of
the heterochronic pathway, the placement of lin-42 in the pathway and its molecular mechanism is unclear. We have found
that one role of lin-42 is to act in parallel with lin-28 to regulate the accumulation of let-7 miRNA. Studies are ongoing to
determine at what step in miRNA biogenesis lin-42 acts and how precocious expression of let-7 affects its targets in the
pathway. In addition, we are using proteomic techniques to identify LIN-42 binding partners that will further elucidate its
role in timing.
Program/Abstract # 386
Plasticity of patterning information in the blastema during limb regeneration in Ambystoma mexicanum
McCusker, Catherine D.; Gardiner, David, University of California at Irvine, United States
The amphibian limb regenerate, called the limb blastema, has the fascinating capacity to replace exactly the missing limb
structures regardless of its location along the proximal/distal limb axis. How is pattern established in the blastema? The
popular hypothesis is that early blastema cells, which are dedifferentiated adult limb cells, retain information about their
original position in the limb and independently establish the pattern of the regenerate. However, ourfindings using GFPlabeled
blastema grafts suggest that the early blastema remains under the influence of the differentiated stump tissue for
patterning information. To understand how changes in the blastema microenvironment correspond to the establishment of
pattern we performed a detailed characterization of the organization of blastema cells, the surrounding extracellular matrix,
and location of cell proliferation in the blastema as it develops. We found that the early blastema and the apical tip of the
lateblastema share a similar microenvironment. By performing additional grafting experiments, we have found that
patterning in the apical tip of the late blastema is plastic, while the basal regions closest to the stump are specified. Our
hypothesis is that patterning information is gradually “hardwired” in the blastema starting with the blastema cells closest to
the differentiated stump. Our current focus is on how the blastema microenvironment controls the level of pattern
commitment in the blastema cells.
Program/Abstract # 387
The role of Notch signaling in neurotransmitter phenotype specification and secondary neurogenesis in X. laevis
McDonough, Molly; Tellis, Athena; Koshiya, Hitoshi; Saha, Margaret, College of William and Mary, Williamsburg,
United States
The acquisition of a neurotransmitter phenotype by individual neurons is crucial for the formation of a functioning nervous
system. During primary neurogenesis, the Notch signaling pathway regulates neural differentiation via lateral inhibition.
We hypothesized that Notch signaling may also regulate the specification of excitatory and inhibitory neurotransmitter
phenotypes. We perturbed Notch signaling by injecting sense mRNA for different components of the pathway into
Xenopus embryos at the two-cell stage. Embryos were then analyzed for gene expression using wholemount ISH. Results
indicate that perturbing components of Notch signaling atearly stages of development does not affect specification of
GABAergic or glutamatergic fates but does alter neural versus non-neural fate differentiation in early stages of
neurogenesis. However, gene expression at later stages of development appears to compensate for these earlier effects. We
utilized qPCR to determine the extent to which that compensation is occurring. Possible mechanisms of compensatory
regulation were analyzed by performing ISH for neural progenitor markers and immunohistochemistry with PCNA to