Differential regulation of epiboly initiation and progression by zebrafish Eomesodermin A

Area of Science:

• Developmental Biology
• Genetics
• Cell Biology

Background:

• Eomesodermin (Eomes) is a T-box transcription factor involved in embryonic patterning and morphogenesis across various species.
• In zebrafish, the Eomesa homolog plays a role in dorsal-ventral patterning, epiboly, and endoderm specification, as suggested by previous overexpression and knockdown studies.

Purpose of the Study:

• To identify and characterize a novel Eomesa mutant in zebrafish using TILLING (Targeting Induced Local Lesions IN Genomes).
• To investigate the specific role of Eomesa in epiboly initiation and progression.
• To explore the cellular mechanisms underlying Eomesa's function in epiboly and endoderm development.

Main Methods:

• Generation of an Eomesa mutant using TILLING.
• Analysis of maternal-zygotic eomesa mutant embryos.
• Microscopic observation of epiboly initiation and progression.
• Examination of yolk cell microtubules and blastoderm deep cell morphology.
• Analysis of endoderm marker gene expression (sox32, bon, og9x).

Main Results:

• Eomesa exhibits a strictly maternal role in the initiation of epiboly (yolk cell doming), but not in its progression.
• Maternal-zygotic eomesa mutant embryos display defective yolk cell microtubules and altered deep cell packing with increased blebbing.
• Eomesa is required for the normal expression of endoderm markers sox32, bon, and og9x, but not essential for endoderm formation itself.

Conclusions:

• Epiboly initiation is genetically separable from epiboly progression, with Eomesa being critical for the former.
• Eomesa likely influences epiboly initiation through its effects on yolk cell microtubules and deep cell adhesion/motility.
• Eomesa is necessary for proper endoderm gene expression, though not for the overall formation of the endoderm.