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Shell-forming cells in limpets are specified autonomously, study finds

Researchers at the University of Tsukuba have examined the developmental fate (the future tissue type) of shell-forming cells in mollusks using blastomere isolation and culture techniques alongside gene expression analysis. The findings are in the journal Development.

They found that in limpets, the fate of shell-forming cells is specified autonomously, rather than through induction by other cell lineages as previously believed.

Mollusks exhibit diverse shell morphologies, such as those seen in bivalves (e.g., clams) and gastropods (e.g., snails). Understanding the mechanisms underlying shell formation requires clarification of how shell-forming cells differentiate during embryonic development.

However, the developmental pathways of these cells remain poorly understood, with several unresolved questions and contradictory hypotheses requiring experimental validation.

In this study, researchers investigated the developmental mechanism of shell-forming cells (shell field cells) in the gastropod Nipponacmea fuscoviridis.

Using single-cell transcriptome and gene expression analyses, they determined that the shell-forming cells at the early larval stage can be classified into at least three distinct types, each expressing characteristic genes. Subsequently, they cultured the blastomeres (cells derived from the cleavage of a fertilized egg) that resulted in shell-forming cells, isolating them from other types of cells.

They found that the developmental fate of all three identified cell types was specified in the absence of contact with other cell lineages. Conventional hypotheses posited that shell-forming cell specification requires interactions with neighboring cells such as endoderms.

However, this study demonstrates that such interactions are not necessary for the initial specification of shell-forming cells in limpets.

The researchers plan to elucidate the mechanisms underlying this autonomous specification and investigate the evolutionary modifications in their functional roles to gain a deeper understanding of how mollusks—and ultimately, animals—have evolved diverse morphologies over time.