Abstract
Background:
Spermatogenesis is a complex process of cell differentiation preceded and accompanied by distinct gene expressions that lead to a variety of cellular and physiological changes. By degrading cyclic adenosine 3′,5′-monophosphate (cAMP), some phosphodiesterases contribute to spermatogenesis by modulating signal transduction across various physiological processes. Although phosphodiesterase 7A (PDE7A) degrades cAMP; its function in the testis as a regulator remains unclear. Furthermore, the exact cell types that express PDE7A at different stages of testicular development remain unknown.

Aim:
This study aimed to study the immunohistochemical localization of the PDE7A protein throughout normal testicular morphogenesis in immature and mature stages in mice, rats, and camels.

Methods:
Testes from immature and pubertal animals were examined to evaluate testicular morphology and the cellular distribution of PDE7A. Immunohistochemistry was performed using a monoclonal antibody directed against the C-terminal portion of PDE7A, and routine hematoxylin and eosin staining was used to assess overall testicular histology.

Results:
In all species, PDE7A protein is successively expressed in specific spermatogenic stages of the immature testis, such as spermatogonia and primary spermatocytes, as well as in the interstitial tissue: Leydig cells, blood vessels, and myoid cells. In mature testes, the PDE7A localization was noted specifically within the round and elongated spermatids of seminiferous tubules, as well as in the endothelial cells lining the blood vessels and peripheral nerve fibers.

Conclusion:
PDE7A expression in the postnatal testis is supported by new evidence in this paper, including the first description of it in camels and its first expression in peripheral nerves. Following meiosis, the enzyme is mostly expressed in germ cells and exhibits stage-specific localization. These findings may point to PDE7A’s regulatory function in spermatogenesis.

Key words: Cyclic adenosine monophosphate; Immunohistochemistry; Phosphodiesterase 7A; Spermatogenesis; Testis.