Expression and promoter analysis of mouse mastrin gene

Splicing variants of NOL4 differentially regulate the transcription activity of Mlr1 and Mlr2 in cultured cells

Mlr1 (Mblk-1-related protein-1) and Mlr2 are mouse homologs of transcription factor Mblk-1 (Mushroom body large-type Kenyon cell-specific protein-1), which we originally identified from the honeybee brain. In the present study, aiming at identifying coregulator(s) of Mlr1 and Mlr2 from the mouse brain, we used yeast two-hybrid screening of mouse brain cDNA library to search for interaction partners of Mlr 1 and Mlr2, respectively. We identified nucleolar protein 4 (NOL4) splicing variants as major interaction partners for both Mlr1 and Mlr2. Among the three murine NOL4 splicing variants, we further characterized NOL4-S, which lacks an N-terminal part of NOL4-L, and NOL4-SΔ, which lacks nuclear localization signal (NLS)-containing domain of NOL4-S. A GST pull-down assay revealed that Mlr1 interacts with both NOL4-S and NOL4-SΔ, whereas Mlr2 interacts with NOL4-S, but not with NOL4-SΔ. These results indicate that the NLS-containing domain of NO4-S Is necessary for in vitro binding with Mlr2, but not for that with Mlr1. Furthermore, a luciferase assay using Schneider's Line 2 cells revealed that transactivation activity of Mlr1 was significantly suppressed by both NOL4-S and NOL4-SΔ, with almost complete suppression by NOL4-SΔ. In contrast, transactivation activity of Mlr2 was significantly suppressed by NOL4-S but rather activated by NOL4-SΔ. Our findings suggest that transactivation activities of Mlr1 and Mlr2 are differentially regulated by splicing variants of NOL4, which are expressed in a tissue-selective manner.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Reduced Mitotic Activity and Increased Apoptosis of Fetal Sertoli Cells in Rat Hypogonadic (hgn/hgn) Testes

Sterility in male hypogonadic (hgn/hgn) rats results from congenital testicular dysplasia caused by a single recessive gene hgn on rat chromosome 10. We recently identified an insertion mutation in the Spag5/astrin gene of hgn/hgn rats that may cause defective proliferation of immature Sertoli cells in the postnatal hgn/hgn testis. Since the pathological alterations were present in the testes at birth, we examined the involvement of defective mitosis and apoptotic cell death in embryonic development of hgn/hgn testes. Testicular hypoplasia was apparent at embryonic day (ED) 18.5. Immunostaining of hgn/hgn testes at ED 21.5 with antibody to GATA-4, which is specific for fetal Sertoli cells in the seminiferous cords, showed that the significant decrease in the number of fetal Sertoli cells was accompanied by a two fold increase in their mitotic index and abnormal mitosis and apoptosis. Prior to this, we observed a decrease in the number of BrdU-labeled cells, an increase in the number of TUNEL-positive apoptotic cells, and presence of MIS-positive apoptotic cells in hgn/hgn testes on ED 17.5 and 18.5. These results suggest that the Spag5 mutation may cause a reduction in mitotic activity and an increase in apoptosis of fetal Sertoli cells in hgn/hgn testes.

Rat Spag5 associates in somatic cells with endoplasmic reticulum and microtubules but in spermatozoa with outer dense fibers

The leucine zipper motif has been identified as an important and specific interaction motif used by various sperm tail proteins that localize to the outer dense fibers. We had found that rat Odf1, a major integral ODF protein, utilizes its leucine zipper to associate with Odf2, another major ODF protein, Spag4 which localizes to the interface between ODF and axonemal microtubule doublets, and Spag5. The rat Spag5 sequence indicated a close relationship with human Astrin, a microtubule-binding spindle protein suggesting that Spag5, like Spag4, may associate with the sperm tail axoneme. RT PCR assays indicated expression of Spag5 in various tissues and in somatic cells Spag5 localizes to endoplasmic reticulum and microtubules, as expected for an Astrin orthologue. MT binding was confirmed both in vivo and in in vitro MT-binding assays: somatic cells contain a 58 kDa MT-associated Spag5 protein. Western blotting assays of rat somatic cells and male germ cells at different stages of development using anti-Spag5 antibodies demonstrated that the protein expression pattern changes during spermatogenesis and that sperm tails contain a 58 kDa Spag5 protein. Use of affinity-purified anti-Spag5 antibodies in immuno electron microscopy shows that in rat elongated spermatids and epididymal sperm the Spag5 protein associates with ODF, but not with the axonemal MTs. This observation is in contrast to that for the other Odf1-binding, MT-binding protein Spag4, which is present between ODF and axoneme. Our data demonstrate that Spag5 has different localization in somatic versus male germ cells suggesting the possibility of different function.

Duplicated insertion mutation in the microtubule-associated protein Spag5 (astrin/MAP126) and defective proliferation of immature Sertoli cells in rat hypogonadic (hgn/hgn) testes

Male rats with hypogonadism (hgn/hgn) experience sterility from testicular dysplasia, which is controlled by a single recessive gene, hgn. The postnatal growth of the seminiferous tubules was severely affected. In this study, we localized thehgnlocus to a 320 kb region on rat chromosome 10 and detected the insertion of a 25 bp duplication into the sixth exon of the sperm-associated antigen 5 (Spag5/astrin/MAP126) gene, which codes for a microtubule-associated protein. This mutation results in a truncatedSpag5protein lacking the primary spindle-targeting domain at the C terminus. Immunological staining with antibodies to markers for Sertoli and germ cells during the early postnatal period indicated that the abnormal mitosis with dispersed chromosomes inhgn/hgntestes occurs in proliferating Sertoli cells. Therefore, apoptotic Sertoli cell death would result from the disorganization of the spindle apparatus caused by defectiveSpag5. These findings suggested that theSpag5is essential for testis development in rats and that thehgn/hgnrat is a unique animal model for studying the function ofSpag5.

Clast4, the murine homologue of human eIF4E-Transporter, is highly expressed in developing oocytes and post-translationally modified at meiotic maturation

In metazoans, translational regulation of a set of maternal mRNAs directs oocyte maturation and early embryogenesis. These transcripts are often kept dormant until their products are spatially and temporally required in development. The interaction between general translation factors (i.e. eIF4E) and their specific interactors influences translation initiation. A search of the protein database for a mouse homologue of the Drosophila Cup protein, a translational repressor during female germ-line development, identified the product of the Clast4 gene. In this report, we show that Clast4 mRNA and protein are highly expressed within the cytoplasm of growing oocytes. The Clast4 protein is stable during this developmental window and post-translationally modified by phosphorylation upon oocyte meiotic maturation. Additionally, we show that Clast4 and eIF4E directly interact by means of a canonical and functional eIF4E-binding motif. Our results suggest that Clast4, similar to Drosophila Cup, may act at the translational level during murine female germ-line development.