Understanding neuroendocrine function requires knowing not only which genes are expressed, but where they act within complex tissues. Bulk transcriptomics averages expression across heterogeneous cell populations, while dissociation-based approaches lose their anatomical context. Spatial transcriptomics addresses this gap by mapping gene expression within intact tissue sections. Here, we explore its application to neuroendocrine organisation and reproductive plasticity using a non-model vertebrate.

We generated spatially resolved transcriptomic maps of the brain of the New Zealand spotty wrasse (Notolabrus celidotus), a fish capable of socially controlled female-to-male sex change. Brain sections sampled before, during and after sex change were used to examine the spatial distribution of gene expression across neuroendocrine regions. Anatomical localisation and cell-type-associated expression patterns provided complementary perspectives on tissue organisation and transcriptional change.

Spatial mapping revealed pronounced heterogeneity in the distribution of candidate genes implicated in reproductive regulation. Transcriptional changes associated with sex change differed across brain regions, including changes in neuropeptide signalling and markers of radial glial cells and neural plasticity. These findings illustrate how retaining anatomical context can distinguish localised molecular responses within a complex tissue and help identify the cellular populations associated with reproductive transitions.

Spatial transcriptomics provides a framework for connecting molecular profiles with tissue architecture, strengthening the interpretation of neuroendocrine gene expression. Beyond sex-changing fishes, this approach offers opportunities to investigate how distinct cellular populations and anatomical regions contribute to reproductive function and plasticity. Our work illustrates its value in non-model organisms and its potential to guide targeted functional studies.