Uncoupling of transcriptomic and cytological differentiation in mouse spermatocytes with impaired meiosis.

Cell differentiation is driven by changes in gene expression that manifest as changes in cellular phenotype or function. Altered cellular phenotypes, stemming from genetic mutations or other perturbations, are widely assumed to directly correspond to changes in the transcriptome and vice versa. Here, we exploited the cytologically well-defined Prdm9 mutant mouse as a model of developmental arrest to test whether parallel programs of cellular differentiation and gene expression are tightly coordinated, or can be disassociated. By comparing cytological phenotype markers and transcriptomes in wild-type and mutant spermatocytes, we identified multiple instances of cellular and molecular uncoupling in Prdm9 mutants. Most notably, although Prdm9 germ cells undergo cytological arrest in a late-leptotene/zygotene stage, they nevertheless develop gene expression signatures characteristic of later developmental substages. These findings suggest that transcriptomic changes may not reliably map to cellular phenotypes in developmentally perturbed systems.