Abstracts - Society for Developmental Biology

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cell proliferation and for normal differentiation of their progeny. We further demonstrate that Edf1 and the cell cycle
regulator Stratifin (Sfn; 14-3-3sigma) act together to regulate keratinocyte differentiation and epidermal barrier formation.
The transcription factor p63 is a master regulator of epidermal development and strongly expressed in the stem cell
compartment. Edf1 mutants, however, exhibit increased levels of p63 throughout the IFE and reduction of p63 dosage in
Edf1 mutants rescues many aspects of the phenotype, indicating that Edf1 modulates p63 levels. Together, our findings
identify Edf1 as a novel regulator of epidermal stem cell proliferation and differentiation that regulates p63 expression and
acts with Sfn to balance these processes.
Program/Abstract # 202
Hh signalling is a key regulator for somatic stem cells in the Drosophila testis
Michel, Marcus; Kupinski, Adam P.; Raabe, Isabel; Boekel, Christian, TU Dresden CRTD, Dresden, Germany
Proper control of stem cell maintenance versus differentiation is essential for tissue homeostasis. In the Drosophila testis a
niche located at the tip regulates two types of stem cells, germline stem cells (GSCs) and cyst stem cells (CySCs), in a
concerted manner. Much light has been shed on how GSCs are regulated, but there is now growing interest in the
regulation of CySCs. Here we show that Hedgehog (Hh) signaling is a key regulator of CySCs in the testis, while only
indirectly affecting GSCs. Loss of Hh signaling in CySCs results in premature differentiation and consequent loss of the
cells. Overactivation of the pathway leads to an increased proliferation and an expansion of the stem cell compartment. As
Hh signaling is also a regulator of the somatic cells in the mammalian testis and the fly ovary this may reflect a higher
degree of homology between these systems than previously expected.
Program/Abstract # 203
Regulating the transition from proliferation towards differentiation in the zebrafish retinal stem cell niche
Cerveny, Kara L., Reed College Biology Department, Portland, United States; Cavodeassi, Florencia (CBMSO, Madrid,
Spain); Turner, Katherine; Gestri, Gaia (London, United Kingdom); Young, Rodrigo (London, United States); Hawkins,
Thomas A; Stickney, Heather L; Wilson, Stephen W (London, United Kingdom)
The eyes of fish grow continuously due to the presence of actively cycling stem cells. These retinal stem cells are
maintained in a small region near the periphery of the eye termed the ciliarymarginal zone (CMZ). Cells within the CMZ
are organized such that the leas tdetermined stem cells are nearest the periphery, the proliferative neuroblasts more medial,
and the post-mitotic differentiating cells adjacent to the central retina. To investigate how CMZ cells transition from
quiescence to proliferation to terminal cell cycle exit and differentiation, we are analyzing zebrafish mutants with small
eyes that fail to grow. In the flotte lotte (flo) mutant, CMZ cells remain proliferative, lose the ability to enter their final,
neurogenic divisions, and subsequently die. Interestingly, when flo mutant cells are transplanted into the CMZ of wild-type
retinae, they progress from proliferation towards differentiation, revealing that the differentiated retinal environment limits
proliferation of precursors emerging from the CMZ. Clues to the identity of one of the signals required for environmentally
enforced differentiation come from our analysis of a new mutant, egghead (egh). In egh embryos, retinoic acid (RA)
synthesis is up-regulated throughout the entire peripheral domain of the CMZ. Increasing RA levels in wild-type eyes
during the period of CMZ neurogenesis blocks retinal growth and promotes precocious cell cycle exit and differentiation.
Together, our data support a model in which extrinsic signals impinge on distinct phases of the cell cycle to maintain the
composition of the CMZ and ensure that an appropriate number of new neurons emerge from the retinal stem cell niche.
Program/Abstract # 204
Fern leaf evolution and development
Vasco, Alejandra, The New York Botanical Garden Genomics, Bronx, United States; Smalls, Tynisha; Moran, Robbin C.;
Ambrose, Barbara A. (The New York Botanical Garden, Bronx, NY, United States)
The evolution and development of leaves in land plants has been debated for more than a century. Multiple lines of
evidence indicate that megaphylls originated independently up to nine times, six of which have occurred within ferns. Most
research on the developmental network necessary to specify leaves has been done on angiosperms, and comparable studies
are largely lacking for ferns. Therefore, questions remain about the homology of megaphylls. To address this gap in our
understanding of fern leaf evolution, we are studying some of the gene families that play a role in angiosperm leaf
development. We are cloning and analyzing two of these genes across ferns: Class-1 KNOX and Class III HD-Zips. Our
analyses include 10 out of 11 orders of extant ferns. Results suggest that both gene families duplicated early in the
diversification of ferns, and at least two copies of each gene family are present in each fern taxa sampled. We have
analyzed the expression patterns of several paralogs of these two families and found that they resemble that of angiosperms
homologs. There are no functional model systems in ferns. Instead, we are using the natural variation of leaf morphology
present in a group of closely related species in the fern genus Elaphoglossum, in an attempt to correlate their leaf