A) Indicadores físico-químicos generales
5. Condiciones de referencia y establecimiento de límites
5.3. Indicadores biológicos
In the work presented herein, we have shown that mir-34 and mir-83 promote robust DTC pathfinding during phase 1 and phase 3 of migration through potential targets cdc-42, pat-3, and peb-1. The role of cdc-42 and pat-3 in DTC migration is well characterized while the role of peb-1 in the process is still to be understood. DTC migration is sensitive to temperature changes, specifically during a two hour time period during the first larval stage that overlaps with the birth of the two DTCs, before migration is initiated. In the absence of mir-34 and mir-83, the three targets are presumably overexpressed causing the DTCs to wander from their proper path. Based on RNAi results, pat-3 misregulation during the two hour temperature-sensitive period leads to migratory
defects, while misregulation of cdc-42 and peb-1 exerts its effects after the two hour period.
In addition to a DTC migration defect, mir-83(n4638); mir-34(gk437) mutants have a reduced lifespan and fecundity defects. The lifespan defect is enhanced by temperature oscillations, therefore it is possible that it is related to the DTC migration defect. Due to the fact that the fecundity defect is not
enhanced by temperature oscillations and is not suppressed by genetic reduction of cdc-42 or pat-3, it is likely the result of mir-34 and mir-83 involvement in a separate pathway.
At this time, we do not understand how C. elegans senses or responds to temperature change. Abolishing the C. elegans classical heat shock response pathway does not affect the penetrance of the migration defect. However,
downstream components of the pathway may still participate in the response. We have established that changes within a temperature range considered standard for the worm are in fact stressful and that C. elegans protects genetic pathways from such changes to ensure robust development. Importantly, our work provides another example of miRNAs promoting robustness in development, an emerging hypothesis for their role in gene expression.
Although the link between changes in temperature and the effect on DTC migration is still unknown, the rate of development in C. elegans is known to be closely tied to environmental temperature [169]. Therefore, it follows that there would be regulatory systems to control developmental timing based on the ability
to sense temperature in ways other than simply enzyme kinetics. Perhaps these regulatory systems are stressed under frequent temperature changes. A wild type worm may subsequently have checks and balances in place such that
temperature fluctuations do not automatically lead to a change in developmental rate. This work suggests that mir-34 and mir-83 perform this role in the DTCs, and raises the question: what miRNAs, if any, protect other tissues and cell types from changing temperature? A critical step in understanding what temperature changes do to the worms is identifying the pathways involved in sensing the changes and those pathways involved in responding to them. These pathways may also shed light on why DTC migration is sensitive to temperature changes in a two hour period hours before migration begins. The fact that the temperature- sensitive period overlaps with the birth of the DTCs suggests that temperature changes affect an early process in the life of the DTCs. While temperature changes do not affect the specification of the DTCs (key functions are still performed, just not to the same standard as wild type) they may lead to aberrations in the initial genetic expression within the cells that subsequently affects the DTCs throughout the cells’ lives. At this time, such discussion is conjecture, but with further study we may begin to understand how temperature changes create a stress, why the DTCs are so sensitive to this stress, and how
C. elegans protects developmental robustness.
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