Characterizing the Genetic Network that Regulates the Temporal and Spatial Cell Migration in C. elegans
Date Issued
2015
Date
2015
Author(s)
Chiang, Min-Ren
Abstract
Cell migration plays an important role during animal development. In the C. elegans hermaphrodite, the shape of the gonad is determined by the migration pattern of two somatic distal tip cells (DTCs). UNC-5 is a netrin receptor that acts as a guidance cue to regulate the DTC dorsalward migration. The transcription factors DAF-12, LIN-29 and BLMP-1 act together to regulate unc-5 expression. Previous studies have shown that LIN-29 and DAF-12 suppress blmp-1 transcription and BLMP-1 negatively regulates unc-5 to control the normal timing of DTC migration. We found that LIN-42, C. elegans Period homolog, represses lin-29 transcription and activates blmp-1 transcription to prevent precocious DTC dorsal migration. Interestingly, blmp-1; daf-12 double mutants displayed a heterogeneous phenotype with a normal, precocious or retarded dorsalward turning. To investigate the causes of this heterogeneous phenotype, we used transcriptional reporter and single molecule fluorescence in situ hybridization (smFISH). We found earlier but lower lin-29 and unc-5 expression in blmp-1; daf-12 double mutants at the specific developmental stages, indicating that the early but low expression of lin-29 possibly propagates to unc-5. These data suggest that BLMP-1 may activate lin-29 expression at DTC turning stage and the heterogeneous phenotype may result from the abnormal expression of lin-29 in blmp-1; daf-12 mutants. We, therefore, developed a mathematical model to examine whether the earlier but lower lin-29 and unc-5 expression cause heterogeneous phenotype in the double mutant. The results indicated the phenotypic variation in blmp-1; daf-12 mutants may result from the lower but noisy expression level of UNC-5 near the threshold of DTC dorsalward turning. Indeed, by manipulating the upstream lin-42 regulators to increase the lin-29 and unc-5 expression, we found the heterogeneous phenotype in blmp-1; daf-12 could be alleviated. The fact that about 30% of DTCs still undergo dorsalward migration in unc-5 null allele suggests that additional guidance system besides UNC-5 exists. No DTCs makes dorsalward migration in daf-12; lin-29 double mutants, therefore, the additional guidance system may be regulated by daf-12 and lin-29. Using the binding consensus sequences of DAF-12 and LIN-29 and a functional test, we identified MIG-6 and INA-1 as components of the guidance system that act in parallel with UNC-5 to direct DTC dorsalward migration. To sum up, our studies establish a comprehensive gene regulatory network consisting of temporal and spatial regulation for the DTC dorsalward migration in C. elegans, and provide the molecular bases for the heterogeneous phenotype observed in the mutants.
Subjects
C. elegans
cell migration
distal tip cell
gonad
Type
thesis