The localization of DGCR8 in spermatogenic cells and sperm from rat and mouse was studied by immunofluorescence and immunoelectron microscopy. Spermatogenic cells from these species yielded similar DGCR8 localization pattern. Immunofluorescence microscopy results showed that DGCR8 localized to both the cytoplasm and nucleus. In the cytoplasm, diffuse cytosolic and discrete granular staining was observed. Dual staining showed that DGCR8 colocalized to the granules with MAEL (a nuage marker). In the nucleus of spermatocytes, both the nucleoli and nucleoplasm were stained, whereas in the nucleus of early spermatids small spots were stained. In late spermatids, DGCR8 localized to the tip of their head and to small granules (neck granules) of the neck cytoplasm. The neck granules were also observed in the neck of epididymal sperm. Immunoelectron microscopy results showed that DGCR8 localized to nuage structures. Moreover, DGCR8 localized to nonnuage structures in late spermatids. DGCR8 also localized to the nucleolus and euchromatin in spermatocytes and round spermatids and to small granules in the nucleus of late spermatids. The results suggest that in spermatogenic cells DGCR8 localizes not only to the nuclei but also to the cytoplasmic structures such as nuage and nonnuage structures. Furthermore, DGCR8 seems to be imported into the egg with neck granules in sperm during fertilization. 1. Introduction Spermatogenesis is a dynamic and highly complicated process that is composed of three phases based on functional aspects: (1) the proliferative phase in which spermatogonia undergo rapid successive cell divisions, (2) the meiotic phase in which recombination and segregation of chromosomes occur, and (3) the differentiation phase, named spermiogenesis, in which spermatids transform into spermatozoa which are specialized to carry haploid genome to the egg [1–3]. During these phases, numerous phase-specific and house-keeping genes are expressed and supply proteins are required for phase-specific functions and usual metabolism in testis [4]. RNA silencing pathway plays important roles in spermatogenesis [5–9]. A key step in this pathway is the processing of double-stranded (ds) RNAs into short RNA duplexes of characteristic size and structures, which is performed by Drosha and Dicer, proteins related to the RNase III family [10–13]. DGCR8 is a protein encoded to the DiGeorge syndrome critical region gene 8 and a subunit of microprocessor complex. It has a nuclear transport signal sequence and usually located in the nucleus, especially in the nucleolus together
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