Forgot your password?
Document Actions
Karen Echeverri
Molecular mechanisms of positional identity and size control during regeneration
Previous and current research
The capacity to regenerate body parts is widely observed throughout the animal kingdom, ranging from salamanders, its true champions, capable of fully regenerating multiple appendages and organs down to humans, which exhibit very poor regenerative abilities. To date, despite its obvious medical potential, very little is understood about this remarkable phenomenon on a molecular level.
A central principle of all salamander regeneration is the generation of a population of pluripotent blastema cells, at least partly through dedifferentiation and migration of cells from neighboring tissues, that will eventually differentiate and faithfully replace the lost structures. If any limb of a urodele is amputated, for example, the animal faithfully regenerates an exact replica of the lost structure. How regeneration is “calibrated” so precisely remains unclear, though it is thought that cells at the cut surface maintain a positional memory of their identity and this stored information is then used to regenerate the missing structures, but the exact molecular basis underlying this process remains poorly understood.
We are focusing on recently identified key post-translational regulators of major programs of gene expression, microRNAs. miRNAs have been shown to be key regulators of gene expression during development. By carrying out microarrays of miRNAs on non-regenerating versus regenerating axolotl tissue we have identified key miRNAs in salamanders that are differentially regulated during regeneration. We have found a core set of microRNAs that are involved in the early stages of both tail and limb regeneration, suggesting a conserved mechanism for initiating the regenerative response and for promoting cells to re-enter cell cycle. We also identified certain microRNAs that are unique to either tail or limb regeneration and others that are involved in both types of regeneration but are differently regulated in tail versus limb.
To enable us to begin to understand the role miRNAs play during regeneration we have established techniques for modulating microRNA function in vivo. By injection of chemical inhibitors into the early blastema or into the cells at the cut surface we can selectively inhibit the formation of select mature microRNAs in the cells of the early blastema. We are also using the same injection technique to manipulate miRNAs that were found to be down regulated in the early blastema, using injection we can over express “mimic miRNAs” during regeneration to examine how the continued presence of these miRNAs effects regeneration.
Using standard bioinformatics analyses and publicly-accessible target prediction algorithms, we are identifying potential targets of all relevant miRNAs, helping to prioritize these for further functional testing using synthetic antagomirs and mimics both in animals in vivo and in cultured blastema cells in vitro.
We are specifically addressing questions of positional identity and size control, how do cells at the cut surface know how much to regenerate and how does the appendage or organ know when to stop growing?
As miRNAs are highly conserved the ultimate goal is to then use the information from studying the molecular mechanisms of regeneration in the salamander to then try to promote regeneration in a mammalian system.
Expression of microRNA 206 in the Axolotl
microRNA 206 is expressed from very early in development, Panel A shows expression of this miRNA in the developing somites from St. 25 to St. 40. In the mature tissue this microRNA is not detected (C) but miRNA 206 can be detected again in the regenerating tissue (C)
Future prospects and goals
To date much research in the regeneration field has focused on studying specific pathways that play a role in regeneration, for example the Wnt pathway. The strategy we are proposing will elucidate many new pathways that are essential to regeneration, along with the post-transcriptional means by which they are regulated. We are using both the axolotl and zebrafish are model systems. We expect this multi-tiered approach will allow us to create a blueprint of the pathways that are essential for telling cells what and how much must be regenerated.
About
 |
|
Selected publications
Sehm T, Sachse, C , Frenzel, C and Echeverri K. miR-196 is an essential early-stage regulator of tail regeneration, upstream of key spinal cord patterning events. (submitted 2008)
Echeverri, K and AC Oates. 2007. Coordination of symmetric cyclic gene expression during somitogenesis by Suppressor of Hairless involves regulation of retinoic acid catabolism. Dev. Biol. Jan 15;301(2):388-403
Echeverri, K and EM Tanaka. 2005. Proximodistal Patterning during Limb Regeneration. Dev. Biol. 279(2):391-401.
Echeverri, K. and EM Tanaka. 2002. Ectoderm to Mesoderm Lineage Switching during Axolotl Tail Regeneration. Science 298: 1993-1996
Echeverri, K., Clarke, JD and EM Tanaka. 2001. In vivo imaging indicates muscle fiber dedifferentiation is a major contributor to the regenerating tail blastema. Dev. Biol. 236 (1):151-64.