Regeneration in the HemichordatePtychodera flava

Abstract

When the body of P. flava is severed, the animal has the ability to regenerate its missing anterior or posterior as appropriate. We have focused on anterior regeneration when the head and branchial regions are severed from the body of the worm. After transection, the body wall contracts and heals closed in 2 to 3 days. By the third day a small blastema is evident at the point of closure. The blastema grows rapidly and begins the process of differentiating into a head with a proboscis and collar. At 5 days the blastema has increased greatly in size and differentiated into a central bulb, the forming proboscis, and two lateral crescents, the forming collar. Between 5 and 7 days a mouth opens ventral to the differentiating blastema. Over the next few days the lateral crescents extend to encircle the proboscis and mouth, making a fully formed collar. By 10 to 12 days a new head, sized to fit the worm's body, has grown attached to the severed site. At about this time the animal regains apparently normal burrowing behavior. After the head is formed, a second blastema-like area appears between the new head and the old body and a new branchial region is inserted by regeneration from this blastema over the next 2 to 3 weeks. The regenerating tissues are unpigmented and whitish such that in-situ hybridization can be used to study the expression of genes during the formation of new tissues.

Evolutionary crossroads in developmental biology: hemichordates

“…The close relationship of hemichordates and chordates suggests that a molecular characterization of regeneration in hemichordates might be very revealing. Enteropneusts have excellent regenerative capacities (Tweedell, 1961;Packard, 1968;Rychel and Swalla, 2008;Humphreys et al, 2010;, and impressive anterior and posterior regeneration has been reported in several ptychoderids (Rao, 1955;Rychel and Swalla, 2008;Humphreys et al, 2010) as well as reproduction by fission (Packard, 1968;.…”

Hemichordate models

“…However, these worms, like hydras and planarians, have amazing regenerative capabilities and they are able to form a complete animal from random portions cut from the body [54]. While iPS and stem cell research in mammals have made remarkable progress recently, regenerative studies in lower animals, especially planarians, have provided fascinating insights into the molecular gene circuitry involved in regeneration and totipotency [55,56].…”

“…While iPS and stem cell research in mammals have made remarkable progress recently, regenerative studies in lower animals, especially planarians, have provided fascinating insights into the molecular gene circuitry involved in regeneration and totipotency [55,56]. Our group and Swalla's lab have just commenced molecular analyses of regeneration in the hemichordate, P. flava, and this work already shows significant promise [54,57,58]. We are excited that powerful, modern, molecular techniques may allow the use of hemichordates to provide a unique perspective in the search for clues about latent regenerative potential in higher chordates, perhaps including humans (Figure 2).…”

Posterior regeneration in Isodiametra pulchra (Acoela, Acoelomorpha)

“…First, we studied specimens on day one and two of regeneration by electron microscopy (see above) and performed BrdU-pulse experiments on sections to evaluate the structure of the blastema and the exact position of cells in the S-phase. Secondly, we tested whether regeneration in I. pulchra is one continuous process, as in most organisms, or occurs in separate waves as in some other organisms [26-28]. To this end we performed 1-hour pulse experiments on each day of regeneration and covered the entire time of regeneration with successive 12-hour continuous-labelling experiments using 5-ethynyl-2’-deoxyuridine (EdU) to make sure not to miss any peaks in proliferation.…”