Abstract
Mouse RC/BTB2 is an unstudied protein of the RCC1 (Regulator of Chromosome Condensation) superfamily. Because of the significant remodeling of chromatin that occurs during spermiogenesis, we characterized the expression and localization of mouse RC/BTB2 in the testis and male germ cells. The Rc/btb2 gene yields two major transcripts: 2.3 kb Rc/btb2-s, present in most somatic tissues examined; and 2.5 kb Rc/btb2-t, which contains a unique non-translated exon in its 5′-UTR that is only detected in the testis. During the first wave of spermatogenesis, Rc/btb2-t mRNA is expressed from day 8 after birth, reaching highest levels of expression at day 30 after birth. The full-length protein contains three RCC1 domains in the N-terminus, and a BTB domain in the C-terminus. In the testis, the protein is detectable from day 12, but is progressively up-regulated to day 30 and day 42 after birth. In spermatids, some of the protein co-localizes with acrosomal markers sp56 and peanut lectin, indicating that it is an acrosomal protein. A GFP-tagged RCC1 domain is present throughout the cytoplasm of transfected CHO cells. However, both GFP-tagged, full-length RC/BTB2 and a GFP-tagged BTB domain localize to vesicles in close proximity to the nuclear membrane, suggesting that the BTB domain might play a role in mediating full-length RC/BTB2 localization. Since RCC1 domains associate with Ran, a small GTPase that regulates molecular trafficking, it is possible that RC/BTB2 plays a role in transporting proteins during acrosome formation.
Highlights
Spermatogenesis can be divided into three stages: spermatogonial mitosis, meiosis of spermatocytes, and spermiogenesis
A cDNA containing the 1668 bp full-length coding region of Rc/btb2 was labeled by 32P-adCTP, the labeled probe was hybridized to a mouse multiple tissue blot which contains mRNAs from the heart, brain, spleen, lung, liver, smooth muscle, kidney and testis
An overnight exposure revealed that Rc/btb2 mRNA is present in the heart, liver, kidney and testis (Figure 1A)
Summary
Spermatogenesis can be divided into three stages: spermatogonial mitosis, meiosis of spermatocytes, and spermiogenesis. Spermatogonia proliferate by mitosis, from which, the last mitotic division of each spermatogonium yields two primary spermatocytes [1]. The meiotic stage comprises two successive divisions. Spermiogenesis occurs after the second meiotic division; the haploid round spermatids differentiate into the species-specific shaped spermatozoon. During this period, major cell restructuring occurs. As a result of these structural changes during spermiogenesis, many testis-specific proteins must be synthesized; these proteins are involved in the regulation of chromosomal packaging, acrosome biogenesis, and flagella formation [5]
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