Abstracts - Society for Developmental Biology

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of p16, a known cyclin kinase inhibitor normally suppressed by H3K27me3 at embryonic stages. The less number of
Purkinje cells also means the less production of mitogen Shh postnatally, which affects the sustaining proliferation of
granule precursor cells and ultimately leads to the hypoplastic growth of mutant cerebellum. RNA-Seq analysis of
embryonic cerebellums revealed that the pan neuronal marker Neurogenin1 (Ngn1) is consistently down regulated at early
embryonic stages in the mutant cerebellum, which accounts for the defective neurogensis of interneurons and Purkinje
cells. Along with the downregulation of Ngn1, several micro-RNAs that are predicated to target Ngn1 are up-regulated in
the mutant cerebellum. We are currently investigating how regulatory networks governed by Polycomb group proteins
control the spatial and temporal neurogenesis in the cerebellar ventricular zone. Taken together, our data indicate that Ezh2
not only controls the proliferation of granule precursor cells but also ensures proper sequential generation of Purkinje cells
and interneurons.
Program/Abstract # 468
Numb mediated trafficking of Cyclic Nucleotide-Gated Channel to rod photoreceptor sensory
Ramamurthy, Vasanth, IRCM, Montreal, Canada; Johanna Mühlhans (University of Erlangen-Nuremberg, Erlangen,
Germany); Demetra Koutroumbas (McGill University, Montreal, Canada); Yun-Zheng Le (Univ of Oklahoma, Oklahoma,
United States); William Hauswirth (University of Florida, United States)
The photoreceptor cell has aspecialized primary cilium, the outer segments (OS), which is a stack of disk membranes
surrounded by a plasma membrane that serves as an exclusive housing unit for a specific pool of proteins involved in
phototransduction. OS are critical for photoreceptor cell function and mutations in genes that affect the development and
integrity of OS often lead to photoreceptor degenerative diseases in humans. The mechanisms regulating protein sorting to
the OS remain unclear. Recent studies have shown that Numb, an endocytic adapter protein, plays a part in regulating
directional protein trafficking in migrating cellsand neurons, raising the possibility that it might be involved in OS protein
sorting. Consistent with this hypothesis, we found that Numb is expressed in a highly polarized manner exclusively in the
calycal process of the photoreceptor, where protein sorting takes place. To study the role of Numb in photoreceptors, we
have conditionally inactivated Numb and Numblike (Nbl; a homolog of Numb) in photoreceptors using a specific Cre
mouse line (Opsin-Cre). Analysis of the conditional double knockouts (cDKO) revealed that the spatial arrangement of the
OS was severely disrupted, which ultimately leads to retinal degeneration. Interestingly, the cDKO show abnormal
accumulation of an OS plasma membrane protein, the cyclic nucleotide gated channel A1 (CNGC-A1), in cell bodies and
inner segments of photoreceptors before retinal degeneration. Importantly, OS proteins localized to the disk membranes
were not affected, suggesting a specific function for Numb in the localization of OS plasma membrane proteins. Our
results indicate that Numb function is required for polarized protein sorting to the plasma membrane of OS in mouse
photoreceptors, and identifies the Numb pathway as a potential player in photoreceptor function and degeneration in
humans.
Program/Abstract # 469
Tissue specific Porcupine deletion reveals a novel role for ectodermal Wnts in musculotendon development
Smith, Aaron, Brigham Young University, Provo, United States; Murtaugh, L. Charles (University of Utah, Salt Lake City,
United States); Barrow, Jeffery R. (Brigham Young Univ, Provo, United States)
The Wnt family of secreted proteins consists of 19 family members (in the mouse) and are known to signal through
multiple pathways that regulate crucial processes in the development of almost all tissues. Dissecting the roles of
individual Wnts has been hampered due to functional redundancy that exist between family members. We made use of a
conditional allele of the O-acyltransferase, Porcupine (Porcn), that is required for the secretion of all Wnt ligands and the
Msx2Cre deleter to eliminate the secretion of all Wnt ligands from the ventral limb ectoderm, ventral abdominal ectoderm,
and urogenital ectoderm. Interestingly, newborn mice lack ventral digital tendons and the most superficial musculature in
the regions of strongest and earliest deletion. Molecular analysis indicates that the initial defect is a loss of TCF4 positive
muscle connective tissue. This leads to the secondary defect of a loss of musculature in the most heavily affected regions.
Tendons are patterned normally initially and then are lost once they reach a developmental stage where they must interface
with musculature. Thus we show a requirement for ectodermal Wnts in the induction of muscle connective tissue.
Program/Abstract # 470
The microRNA pathway and its central role in the hypoxia response in Drosophila melanogaster
Bertolin, Agostina; De Lella Ezcurra, Ana; Dekanty, Andres; Wappner, Pablo, Instituto Leloir, Ciudad Autonoma de
Buenos Aires, Argentina
The hypoxia-inducible factors (HIFs) are a highly conserved family of transcription factors that constitute the major
regulators of cellular oxygen homeostasis throughout the animal kingdom. We have previously defined a hypoxia-