Origin, viability, and cell cycle status of seminal somatic cells for potential application in cattle cloning via nuclear transfer.

Seminal somatic cells (SSCs) represent promising donor nuclei for cloning by somatic cell nuclear transfer (SCNT), particularly for genetic conservation. This study aimed to identify and characterize SSCs present in bovine semen, determine their possible tissue origins, and evaluate their suitability for cloning. SSCs were isolated using sucrose or mini-Percoll® density gradients and analyzed for morphology, viability, and cell cycle status, as well as their potential use in SCNT cloning. Cytological and histological assessments of the bovine genitourinary tract were performed side-by-side to identify the anatomical origins of each SSC type, and epithelial marker expression was examined by RT-qPCR in SSCs, urethral, and bladder tissues. The mini-Percoll® gradient efficiently separated SSCs from sperm cells, concentrating viable somatic cells in the 20 % fraction. Three SSC types were identified (polygonal, round, and elongated), with polygonal cells being the most abundant and highly viable (>90 %), although they failed to adhere or proliferate in culture. Flow cytometry revealed that most polygonal SSCs (89 %) were arrested at the G0/G1 phase, indicating cell-cycle compatibility for cloning, although with low membrane fusion capacity in SCNT assays. Cytological, histological, and molecular findings collectively indicate that polygonal SSCs most likely originate from the non-keratinized stratified epithelium of the urethral navicular fossa, whereas round and elongated SSCs may derive from the proximal urethra and the ampullary-vesicular-ductal complex, respectively. These results provide a comprehensive anatomical and molecular characterization of SSC subtypes in bovine semen, offering a foundation for improving SCNT cloning standardization and applications in genetic preservation.