Germ plasm in Eleutherodactylus coqui, a direct developing frog with large eggs

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Molecular Biology

Background:

• RNAs are localized to the vegetal cortex in Xenopus laevis oocytes for embryo patterning and germ cell specification.
• In Eleutherodactylus coqui, orthologous RNAs are not localized, posing questions about germ plasm localization in this species.

Purpose of the Study:

• To investigate the presence and localization of germ plasm components in Eleutherodactylus coqui embryos.
• To determine if Eleutherodactylus coqui utilizes germ plasm for primordial germ cell specification.

Main Methods:

• Germ plasm identification using DiOC6(3) staining and in situ hybridization for dazl and DEADSouth RNAs in E. coqui embryos.
• Cloning of E. coqui orthologue cDNAs via RT-PCR.
• Functional analysis of E. coqui RNA 3'UTRs by injecting synthesized RNAs into X. laevis embryos.

Main Results:

• Numerous small islands, indicative of germ plasm, were observed at the vegetal surface of cleaving E. coqui embryos.
• Dazl expression was detected in primordial germ cells within the genital ridge.
• The 3'UTRs of E. coqui dazl and DEADSouth promoted germ cell-specific protein synthesis in X. laevis.

Conclusions:

• Eleutherodactylus coqui employs germ plasm with vegetal cortex-localized RNAs for primordial germ cell specification.
• The abundance of germ plasm islands may have been crucial for the evolutionary development of the large E. coqui egg.