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Early cranial patterning in the direct-developing frog Eleutherodactylus coqui revealed through gene expression
Ryan Kerney1, Joshua B Gross, James Hanken
1Department of Biology, Dalhousie University, 1355 Oxford St., Halifax, NS, Canada B3H 4J1. ryankerney@gmail.com
Evolution & Development
|July 13, 2010
Summary
This study reveals early skeletal gene expression in direct-developing frogs, uncovering transient structures and modified cranial development. These findings offer new insights into amphibian evolution and developmental repatterning.
Area of Science:
- Developmental Biology
- Evolutionary Biology
- Genetics
Background:
- The evolution of amphibian direct development involves genetic and developmental changes, particularly in skeletal development, which are not well understood.
- Key skeletal regulatory genes and their expression patterns during cranial ontogeny in direct-developing species are largely unexplored.
Purpose of the Study:
- To investigate the expression patterns of skeletal regulatory genes (runx2, sox9, bmp4) and col2a1 during cranial development in the direct-developing anuran, Eleutherodactylus coqui.
- To identify early modifications in cranial ontogeny and validate/modify previous findings on larval recapitulation and developmental repatterning.
Main Methods:
- Examined expression patterns of runx2, sox9, bmp4, and col2a1 during cranial development in Eleutherodactylus coqui embryos.
- Utilized gene expression markers to detect transient skeletogenic anlagen and bone precursors.
- Compared expression patterns with those in the metamorphosing species Xenopus laevis.
Main Results:
- Identified transient suprarostral anlagen expressing runx2, sox9, and bmp4, which fuse to cranial trabeculae before detectable by col2a1 staining.
- Observed the absence of an early anterior connection between the palatoquadrate and neurocranium, indicating loss of larval quadratocranial commissure cartilage.
- Detected dermal bone precursors via runx2 expression significantly earlier than with alizarin red staining, correlating with accelerated embryonic bone formation.
Conclusions:
- Gene expression patterns provide an earlier depiction of cranial patterning in Eleutherodactylus coqui.
- The study validates and modifies previous understandings of larval recapitulation and developmental repatterning in anuran direct development.
- Early expression of skeletal genes offers crucial insights into the evolutionary modifications of cranial ontogeny in direct-developing amphibians.
