Spermatogenesis is a continuous process that generates sperm in the mammalian testes. This involves the mitotic expansion of spermatogonia, meiotic division of spermatocytes and cellular differentiation of spermatids from round to elongated within the seminiferous tubules. Chromatin compaction and transcriptional arrest coincide with the transition from round to elongating spermatids. Consequently, previously transcribed mRNA must be maintained and post-transcriptionally controlled to initiate cell-cycle and morphological changes within the later stages of spermatogenesis. To determine the role that cytoplasmic polyadenylation plays in such post-transcriptional processing, CRISPR papolb-/- mice were generated. PAPOLB is a testes-specific cytoplasmic poly(A)-polymerase that is required for spermatogenesis and male fertility in mice. Histological analysis revealed that no elongating or elongated spermatids were present in the seminiferous tubules of testes lacking PAPOLB. Therefore, spermatogenesis appears to fail at the round spermatids stage in concert with transcriptional arrest in the papolb-/- male mice. Poly(A)-focused RNA-sequencing (PAT-seq) of papolb-/- testes demonstrated significant changes to gene expression, poly(A) tail length and alternative polyadenylation. Comparison to testes single cell RNA-sequencing data from the Marioni lab (Ernst et al. 2018) showed that such PAPOLB mRNA targets were primarily expressed in round spermatids. Consequently, PAPOLB appears to play a key role in the post-transcriptional processing of mRNA required for spermatogenesis to proceed past the round spermatid stage.