Characterization of the nutritional endoderm in Eleutherodactylus coqui

Uma Karadge

Defense Date

8-1-2012

Graduation Date

Fall 1-1-2012

Availability

Immediate Access

Submission Type

dissertation

Degree Name

PhD

Department

Biological Sciences

Committee Chair

Richard P Elinson

Committee Member

John A Pollock

Committee Member

Kyle Selcer

Committee Member

Michael Tsang

Keywords

Direct development, Nutritional endoderm, TGFbeta

Abstract

In a Xenopus laevis embryo, VegT induces nodal related TGFbeta signaling, culminating in expression of Sox17, the endoderm specifier. Eleutherodactylus coqui is a direct developing frog and lacks a tadpole stage. In E. coqui, unlike X. laevis, the yolk-rich vegetal region lacking in EcVegT and EcVg1 RNAs functions as a nutritive tissue (NE: Nutritional Endoderm) only. The definitive endoderm (DE) comes from cells closer to the animal pole. I explored differences between NE and DE and asked whether lack of TGFbeta signaling is involved in the formation of NE. Presumptive NE cells in E. coqui become binucleated at blastula. Multinucleation starts at gastrula and increases gradually until the frogs hatch. Similar to X. laevis, beta catenin, a transcriptional cofactor of Sox 17, shows nuclear localization in prospective DE at gastrula, but intriguingly in the NE as well. Accumulation of beta catenin in NE continues in advanced stages of development. I cloned E. coqui homologs of TGFbetas Activin B and derriere and showed that they are both expressed maternal in NE. At early gastrulation, there is relatively more EcActivin B RNA in NE than in DE and zygotic expression of EcDerriere. I also observed some mesoderm inducing activity in NE at NF11 and 12. In an attempt to phenocopy NE in X. laevis, I inhibited and overexpressed nodal signaling in a presumptive X. laevis DE cell. Blocking nodal signaling did not make an NE-like cell in X. laevis while overexpression of Activin B led to yolk retention in tadpole guts. Overall, I identified the differences arising between DE and NE with respect to multinucleation and stabilization of beta catenin. Although deviant in nature, NE expresses TGFbetas and possesses some mesoderm inducing activity.

Format

PDF

Language

English

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