Our laboratory is interested in understanding cell migration during the gastrulation stage of embryogenesis. We identified
pmr-1, a secretory protein calcium ATPase, as playing an essential role in migration during this stage. Disruption of
pmr-1 causes cell migration failures in multiple locations, including C lineage muscle and hypodermal precursors, ventral neuroblasts, and cells in the head during the gastrulation stage of development. Using a hypomorphic allele of
pmr-1, we carried out genetic suppressor screens to identify other genes that play a role in these cell migration events. Whole genome mapping and sequencing of lines obtained in our screen show the
kez13 suppressor allele has a 5kb deletion that eliminates two HOT spots in the 5'UTR of
sma-9.
sma-9 encodes a transcription factor known to act downstream of TGF beta signaling (Liang, et al 2003). The
sma-9(
wk55) allele fails to complement
kez13. Based on its identification in the screen, we asked whether
sma-9 plays a role in embryos. A
sma-9::GFP fusion containing the sequence deleted in
kez13 strains is expressed in migrating cells, as migration is occurring (EPIC database) and
wk55 strains have modest but significant levels of embryonic lethality. Both results are consistent with a role for
sma-9 in embryos. Further evidence for an interaction between the two genes comes from qPCR gene expression studies. While
pmr-1 gene expression is unaffected in
kez13 strains, we observed a significant decrease in
sma-9 mRNA expression in
pmr-1(
ru5) adults, an effect partially suppressed in the
kez13 suppressor line. The 5kb deletion in
kez13 alone decreases
sma-9 mRNA levels modestly, but significantly. These results suggest a complex regulatory mechanism for
sma-9 gene expression that may be dependent on cytosolic calcium levels. Since
sma-9 plays a key role in body size, we asked whether
pmr-1 and
kez13 affect body size. While the
kez13 strain is similar to the wild type control,
pmr-1(
ru5) strains have modest but significant reductions in larval body size These results indicate
pmr-1 may influence a process antagonistic to that of
sma-9, since
pmr-1(
ru5) partially suppresses the body size phenotype in
sma-9(
wk55) strains. Our results have identified a new role for
sma-9 in embryogenesis, and point to a mechanism whereby
sma-9 expression and activity is sensitive to changes in cytosolic calcium levels.