User:Ebayala06/sandbox

This is a sandbox created to organize all my edits for the topic of butterfly eyespots in the Wikipedia live article, Eyespot (mimicry). I copied the information from the original article to organize all the old and new information.

Morphogenetic models

Eyespot patterning is thought to occur by morphogenetic activity, however the exact model and modes of action have yet to be elucidated. A number of experiments have been done to understand the mechanism of eyespot patterning all of which indicate morphogenetic activity.

Effects of cautery on the butterfly wing eyespot foci are indicative of a long range signaling mechanism or morphogen gradient, both in its spatial and temporal aspects. Cautery studies have shown that different results in eyespot size and color can result depending on the time in development at with the cauterizing damage is administered. While these findings support morphogenetic activity, they cannot simply be explained by a source/diffusion model. Observations of cautery have given rise to two different explanations of how eyespots are patterned: 1) A source/threshold model, in which the focus is the morphogen source and, 2) the sink model, in which the focus is generating a gradient by removal of the morphogen at the foci. Several genes involved in eyespot formation have been identified that can fit into these models, but only two of them have been functionally tested. These genes are the transcription factor Distal-less (Dll) and the ligand Hedgehog (Hh)

Distalless

Distalless (Dll) is present in almost all eyespot organizers, making it an ideal candidate to carry out major functions of the eyespot formation. During the wing imaginal disc development Dll, has two expression domains separated by a temporal component. First Dll is expressed in a group of cells in the center of what will become the focus and eventually the eyespot. This expression starts during the middle of the fifth instar larva and lasts until the pupal stage. The second domain starts around 20 hours after pupation around the original central cluster of cells, in an area in which a black ring of the eyespot will be formed. Functional experiments using transgenic B. anynana have shown that overexpression or down-regulation of Dll in the first expression domain correlates with bigger and smaller eyespots respectively. However if this is done on the second domain then the overall size of the eyespots remains the same but the width of the black ring raises with a higher amount of Dll. This suggest that Dll might be responsible for the differentiation of the focus in the first expression domain and might be involved in establishing the ring color patters in the second domain. These experiments together with the wide distribution of Dll across eyespot forming butterflies suggest that this transcription factor is a central regulator for the correct patterning of the eyespots (Monteiro, 2015).

Hedgehog

The hh gene is the other element that has been functionally tested in the formation of eyespots. Investigating genes involved in wing development and morphogenetic activity has led to the discovery that hh has a primary role in the morphogenetic signaling center of the foci. In a manner that is similar to Drosophila, hedgehog (Hh) is expressed in all cells in the posterior compartment of the developing butterfly wing during the mid fifth instar of butterfly wing development. However, in butterflies hh expression is significantly higher in those cells that flank the potential foci. Higher transcription levels of hh along with other known associates of the hh pathway; patched (ptc) the hh receptor, and cubitus interruptus (ci) the hh transcription factor are seen throughout the mid to late fifth instar as well, which further implies a role for hedgehog signaling in eyespot development and patterning. Furthermore, cells that are flanked by the cells expressing the highest level of hh signaling, are fated to become the foci, indicating that foci cell fate determination relies on high concentrations of hh in surrounding cells. However this observation haven’t been totally confirmed as a rule for multiple butterfly species (Monteiro, 2015). Studies tried to extrapolate the result of Hh pathway involvement by looking for the expression of Ci in Bicyclus anynana (Keys, et al., 1999). Here they observed that both seem to be expressed in eyespots suggesting a relation with Hh signaling pathway however this relationship was challenge by lack of Hh expression evidence in B. anynana presented in other studies(Monteiro, 2015).

Notch Other studies have shown that Notch (N) expression precedes an upregulation of dll in cells that will become the center of the focus. This makes N the earliest developmental signal, so far studied, that is related with the establishment of the eyespots. Furthermore loss of N completely disrupts dll expression and eventually eyespots formations in several butterfly species. More interestingly a variety of other wing patterns are determined by N and Dll patterns of expression in early development of the wing imaginal disc suggesting a common mechanism to pattern multiple coloration structures of the wing (Reed & Serfas, 2004).