Immunolocalization of TAR DNA-binding protein of 43 kDa (TDP-43) in mouse seminiferous epithelium.

TAR DNA-binding protein of 43 kDa (TDP-43) is an evolutionarily conserved, ubiquitously expressed, multi-functional DNA/RNA-binding protein with roles in gene transcription, mRNA splicing, stability, transport, micro RNA biogenesis, and suppression of transposons. Aberrant expression of TDP-43 in testis and sperm was recently shown to be associated with male infertility, which highlights the need to understand better the expression of TDP-43 in the testis. We previously cloned TDP-43 from a mouse testis cDNA library, and showed that it functions as a transcriptional repressor and regulates the precise spatiotemporal expression of the Acrv1 gene, which encodes the acrosomal protein SP-10, during spermatogenesis. Here, we performed immunoblotting and immunohistochemistry of the mouse testis using four separate antibodies recognizing the amino and carboxyl termini of TDP-43. TDP-43 is present in the nuclei of germ cells as well as Sertoli cells. TDP-43 expression begins in type B/intermediate spermatogonia, peaks in preleptotene spermatocytes, and becomes undetectable in leptotene and zygotene spermatocytes. Pachytene spermatocytes and early round spermatids again express TDP-43, but its abundance diminishes later in spermatids (at steps 5-8). Interestingly, two of the four antibodies showed TDP-43 expression in spermatids at steps 9-10, which coincides with the initial phase of the histone-to-protamine transition. Immunoreactivity patterns observed in the study suggest that TDP-43 assumes different conformational states at different stages of spermatogenesis. TDP-43 pathology has been extensively studied in the context of neurodegenerative diseases; its role in spermatogenesis warrants further detailed investigation of the involvement of TDP-43 in male infertility.