Identification of specific marker proteins in cells is useful for isolating cells and determining their cellular characteristics and functions. Based on our previous study showing that matrix metalloproteinase 9 (MMP-9) can be used as a marker for porcine spermatogonia, the expression pattern of MMP-9 was determined in both pre- (5-month old) and post-pubertal (11–month old) bovine testes. Histological analysis revealed that spermatogonia were located near the basement membrane in both testes, while spermatozoa were not detected in the 5-month old pre-pubertal bovine testes and epididymides. Mature spermatozoa were observed in the 11-month bovine testes and epididymides, and MMP-9 expression in 11-month old bovine testes was lower than 5-month old testes, according to reverse transcription-PCR and real-time-PCR data. To determine the specific expression sites of MMP-9 in the bovine testes, immunohistochemistry was performed. Expression of MMP-9 was observed in cells near the basement membrane of seminiferous tubules in both 5- and 11-month old testes. Furthermore, MMP-9 positive cells expressed protein gene product 9.5 (PGP9.5) and deleted in azoospermia (DAZL) that are already known as bovine spermatogonial stem cells markers. In the present study, MMP-9 expression was identified in both pre- and post-pubertal bovine spermatogonia expressing PGP9.5 and DAZL, and located near the basement membrane of seminiferous tubules. Thus, MMP-9 can be used as a marker for bovine spermatogonia, and may provide useful platforms for understanding the interaction between germ cells and extracellular matrix during spermatogenesis in the seminiferous tubules.

The insulin-like growth factor (IGF) pathway is a key signal transduction pathway involved in cell proliferation, migration, and apoptosis. In dairy cows, IGF family proteins and binding receptors, including their intracellular binding partners, regulate mammary gland development. IGFs and IGF receptor interactions in mammary glands influence the early stages of mammogenesis, i.e., mammary ductal genesis until puberty. The IGF pathway includes three major components, IGFs (such as IGF-I, IGF-II, and insulin), their specific receptors, and their high-affinity binding partners (IGF binding proteins [IGFBPs]; i.e., IGFBP1–6), including specific proteases for each IGFBP. Additionally, IGFs and IGFBP interactions are critical for the bioactivities of various intracellular mechanisms, including cell proliferation, migration, and apoptosis. Notably, the interactions between IGFs and IGFBPs in the IGF pathway have been difficult to characterize during specific stages of bovine mammary gland development. In this review, we aim to describe the role of the interaction between IGFs and IGFBPs in overall mammary gland development in dairy cows.