HeOtx expression in an indirectly developing polychaete correlates with gastrulation by invagination

Area of Science:

• Developmental Biology
• Marine Biology
• Genetics

Background:

• Otx genes are conserved transcription factors involved in anterior development across bilaterians.
• Understanding Otx expression in marine invertebrates like polychaetes provides insights into evolutionary developmental biology.
• Hydroides elegans, an indirectly developing polychaete, offers a model for studying larval development and gene function.

Purpose of the Study:

• To characterize the expression patterns of an Otx homolog (HeOtx) in the polychaete Hydroides elegans.
• To investigate the potential roles of HeOtx during embryonic, trochophore, and larval feeding stages.
• To compare HeOtx expression with Otx homologs in other polychaetes with different developmental strategies.

Main Methods:

• Whole-mount in situ hybridization was used to detect HeOtx transcripts in Hydroides elegans embryos and larvae.
• Expression patterns were analyzed across distinct developmental stages, including blastula, gastrula, trochophore, and feeding larva.
• Comparative analysis of HeOtx expression was performed with existing data from other polychaete species.

Main Results:

• HeOtx is initially expressed in animal hemisphere blastomeres and later in precursors for adult cerebral ganglia and eyes.
• Expression is observed in cells adjacent to the ciliary band and in dorsal midline cells of the trochophore larva, potentially sensory precursors.
• Vegetal hemisphere expression begins at the blastopore and expands, with HeOtx maintained in midgut precursors, suggesting a role in gut subdivision.

Conclusions:

• HeOtx expression patterns in Hydroides elegans suggest roles in larval cell-type specification, adult brain regionalization, and gut development.
• The broader and earlier endoderm expression in H. elegans correlates with gastrulation by invagination, contrasting with species undergoing epiboly.
• These findings support an ancestral role for Otx in gastrulation by invagination across bilaterians.