Abstracts - Society for Developmental Biology

57
Program/Abstract # 173
The role of non-muscle myosins in C. elegans gonad architecture
Pisio, Amanda; Kachur, Torah; Pilgrim, Dave, University of Alberta, Edmonton, Canada
Non-muscle myosins (NMM) are hexamers of heavy, essential light and regulatory light chains that use ATP to move actin
filaments. NMMs play a role in many processes, such as cytokinesis, where they form actomyosin complexes that lead to
cell shape changes. C. elegans have two non-muscle myosins, NMY-1 and NMY-2. NMY-2 has been studied in numerous
processes in the worm; however NMY-1 has only been studied during elongation of the embryo where it is redundant with
NMY-2. NMMs are mostly regulated through phosphorylation of their regulatory light chain by upstream kinases and
phosphatases. While C. elegans has two genes encoding NMM heavychains, the only known regulatory light chain is
MLC-4. We would expect, therefore, that in tissues where both NMM heavy chains are expressed, NMY-1 and NMY-2
hexamers will be co-ordinately regulated through MLC-4. We can examine this prediction in the C.elegans gonad. At the
distal tips of the gonads, mitotic germ cells are syncytial and as they migrate towards the proximal end of the gonad they
mature into oocytes, grow in size and, close the ring channel that attached them to the syncytium. The gonads of nmy-2
mutants entirely lack this cellularization process, and therefore no oocytes are formed. In contrast, in nmy-1 mutants the
gonads show a premature cellularization of the oocytes. This difference in phenotype may indicate that the two myosins
work in opposition which is interesting considering they share the same regulatory light chain. However, in order to answer
questions involving the regulation of these two opposing myosins, it is necessary to first localize the proteins and
characterize the effect of their loss. I shall be presenting the results of this characterization.
Program/Abstract # 174
Profilin controls soma-germline interaction and differentiation upon exit from the stem cell niche in
the Drosophila testes
Fairchild, Michael J.; Tanentzapf, Guy, University Of British Columbia, Vancouver, Canada
The Drosophila testes house a stem cell niche containing both somatic and germline stem cells that regulate each other’s
proliferative capacity. Upon exit from the stem cell niche the soma encapsulates the germline. This association and
communication between the somatic and germline daughter cells ensures proper differentiation of the germline into mature
spermatids. In order to better understand the morphogenic events underlying regulation of stem cell maintenance and
differentiation we undertook a forward genetic screen of all cytoskeletal genes in the somatic cells of the testes using tissue
specific RNAi knockdowns. Using sterility as a phenotypic assay we identified upwards of 25 cytoskeletal genes required
in the soma, among them chickadee, the Drosophila homologue of the actin binding protein profilin which we analyzed in
detail. We found that profilin is enriched in the somatic cells of the testes, both in the somatic stem cells and their early
daughter cells during germline encapsulation. As profilin is an essential gene we investigated somatic cell survival and
found that profilin deficient somatic cells not only survive but also overproliferate. While profilin deficient somatic cells
were often found to be in contact with the germline we found that some germline cells were not encapsulated, forming
germline tumors. We found that this may be due to profilin deficient somatic cells having defects in EGFR-MapK signal
transduction which controls germline encapsulation. We further analyzed the tumors formed by unencapsulated germline
cells and found them to express a range of spermatogonial markers as well as germline stem cell markers that are usually
spatially restricted to the stem cell niche.
Program/Abstract # 175
Gap Junction-Mediated Regulation of Germline Differentiation and Soma Proliferation
Smendziuk, Christopher M.; Messenberg, Anat; Islam, Fayeza; Tanentzapf, Guy, University of British Columbia,
Vancouver, Canada
In animals, two tissue types populate the gonads: the germline, which gives rise to gametes, and the soma, which gives rise
to all other tissues that support gamete formation. Gametogenesis is a complex process requiring intricate cooperation
between the soma and germline. A key feature of gametogenesis is the involvement of two specialized stem cell
populations that produce the soma and the germline. Stemcells in the testes of Drosophila melanogaster serve as a superb
model system to dissect the cellular and molecular mechanisms that regulate stem cells. Studies in the fly testis have
illustrated that soma-germline interactions control stem cell behaviour and we wish to explore the mechanisms that
underlie soma-germline interactions. Flies containing mutations in the gene zero population growth/innexin4 (zpg) are
sterile and possess tiny gonads. Zpg encodes an innexin, a gap junction protein. Previous studies indicate that Zpg
functions in the germline to regulate germline stem cells but the precise role of Zpg has not yet been elucidated. Our
preliminary data supports the idea that Zpg may mediate signalling from the germline to the soma. We have uncovered
previously uncharacterized defects in the soma in zpg mutants, including overproliferation. In addition, we have analyzed
the function of the eight Drosophila innexins in the testes. Our observations support the assertion that Zpg helps form gap