Limits...
The Arf GAP SMAP2 is necessary for organized vesicle budding from the trans-Golgi network and subsequent acrosome formation in spermiogenesis.

Funaki T, Kon S, Tanabe K, Natsume W, Sato S, Shimizu T, Yoshida N, Wong WF, Ogura A, Ogawa T, Inoue K, Ogonuki N, Miki H, Mochida K, Endoh K, Yomogida K, Fukumoto M, Horai R, Iwakura Y, Ito C, Toshimori K, Watanabe T, Satake M - Mol. Biol. Cell (2013)

Bottom Line: In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis.Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation.Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Immunology, Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai 980-8575, Japan.

ABSTRACT
The trans-Golgi network (TGN) functions as a hub organelle in the exocytosis of clathrin-coated membrane vesicles, and SMAP2 is an Arf GTPase-activating protein that binds to both clathrin and the clathrin assembly protein (CALM). In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis. Gene targeting reveals that SMAP2-deficient male mice are healthy and survive to adulthood but are infertile and exhibit globozoospermia. In SMAP2-deficient spermatids, the diameter of proacrosomal vesicles budding from TGN increases, TGN structures are distorted, acrosome formation is severely impaired, and reorganization of the nucleus does not proceed properly. CALM functions to regulate vesicle sizes, and this study shows that CALM is not recruited to the TGN in the absence of SMAP2. Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation. Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation. SMAP2-deficient mice provide a model for globozoospermia in humans.

Show MeSH

Related in: MedlinePlus

Electron microscopic observations of acrosome formation and subsequent events in wild-type and SMAP2-targeted germ cells. Cells at the cap, acrosome, and maturation phases of acrosome formation are shown. Sections of epididymides are also shown. See the text for the description of structural abnormalities. A, axoneme; Ac, acrosome; Apx, acroplaxome; G, Golgi apparatus; M, mitochondria; N, nucleus; Sc, Sertoli cell. Arrowheads in IV and V are marginal rings. Asterisks in IV and VII–IX are manchettes. Double white arrows in IV and VII are ectoplasmic specializations derived from Sertoli cells. White arrows indicate pseudoacrosomes (II), a disorganized TGN structure (III), interrupted ectoplasmic specializations (V), invagination of a Sertoli cell into the germ cell (VI), and fragmented acrosomes (VIII). Bars, 1 μm (I–IX), 2 μm (X, XI).
© Copyright Policy - creative-commons
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3756916&req=5

Figure 6: Electron microscopic observations of acrosome formation and subsequent events in wild-type and SMAP2-targeted germ cells. Cells at the cap, acrosome, and maturation phases of acrosome formation are shown. Sections of epididymides are also shown. See the text for the description of structural abnormalities. A, axoneme; Ac, acrosome; Apx, acroplaxome; G, Golgi apparatus; M, mitochondria; N, nucleus; Sc, Sertoli cell. Arrowheads in IV and V are marginal rings. Asterisks in IV and VII–IX are manchettes. Double white arrows in IV and VII are ectoplasmic specializations derived from Sertoli cells. White arrows indicate pseudoacrosomes (II), a disorganized TGN structure (III), interrupted ectoplasmic specializations (V), invagination of a Sertoli cell into the germ cell (VI), and fragmented acrosomes (VIII). Bars, 1 μm (I–IX), 2 μm (X, XI).

Mentions: The later phases of acrosome formation were examined by TEM (Figure 6). In the cap phase in wild-type cells (Figure 6, I), proacrosomal vesicles that had budded from the TGN fused with each other and formed a large acrosome (Ac) located at the acroplaxome (Apx), a unique substructure composed of keratin and actin that serves as a site for anchoring the acrosome to the nuclear membrane (Kierszenbaum et al., 2003). By contrast, in a cap-phase SMAP2-targeted cell (Figure 6, II), acrosomes of intermediate size were formed but never fused to form one large acrosome and remained as multiple pseudoacrosomes (indicated by the arrows). These pseudoacrosomes attached to multiple sites on the nuclear envelope. In another SMAP2-targeted cell (Figure 6, III), one acrosome appeared to be formed but was greatly enlarged in size (the TGN was also disorganized and partly distended; arrows). These observations indicate that acrosome formation from proacrosomal vesicles in SMAP2-deficient cells is disrupted, even though the acroplaxome structures are well organized on the nuclear lamina. Therefore it is unlikely that a defect in the acroplaxome caused the aberrant acrosome formation.


The Arf GAP SMAP2 is necessary for organized vesicle budding from the trans-Golgi network and subsequent acrosome formation in spermiogenesis.

Funaki T, Kon S, Tanabe K, Natsume W, Sato S, Shimizu T, Yoshida N, Wong WF, Ogura A, Ogawa T, Inoue K, Ogonuki N, Miki H, Mochida K, Endoh K, Yomogida K, Fukumoto M, Horai R, Iwakura Y, Ito C, Toshimori K, Watanabe T, Satake M - Mol. Biol. Cell (2013)

Electron microscopic observations of acrosome formation and subsequent events in wild-type and SMAP2-targeted germ cells. Cells at the cap, acrosome, and maturation phases of acrosome formation are shown. Sections of epididymides are also shown. See the text for the description of structural abnormalities. A, axoneme; Ac, acrosome; Apx, acroplaxome; G, Golgi apparatus; M, mitochondria; N, nucleus; Sc, Sertoli cell. Arrowheads in IV and V are marginal rings. Asterisks in IV and VII–IX are manchettes. Double white arrows in IV and VII are ectoplasmic specializations derived from Sertoli cells. White arrows indicate pseudoacrosomes (II), a disorganized TGN structure (III), interrupted ectoplasmic specializations (V), invagination of a Sertoli cell into the germ cell (VI), and fragmented acrosomes (VIII). Bars, 1 μm (I–IX), 2 μm (X, XI).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756916&req=5

Figure 6: Electron microscopic observations of acrosome formation and subsequent events in wild-type and SMAP2-targeted germ cells. Cells at the cap, acrosome, and maturation phases of acrosome formation are shown. Sections of epididymides are also shown. See the text for the description of structural abnormalities. A, axoneme; Ac, acrosome; Apx, acroplaxome; G, Golgi apparatus; M, mitochondria; N, nucleus; Sc, Sertoli cell. Arrowheads in IV and V are marginal rings. Asterisks in IV and VII–IX are manchettes. Double white arrows in IV and VII are ectoplasmic specializations derived from Sertoli cells. White arrows indicate pseudoacrosomes (II), a disorganized TGN structure (III), interrupted ectoplasmic specializations (V), invagination of a Sertoli cell into the germ cell (VI), and fragmented acrosomes (VIII). Bars, 1 μm (I–IX), 2 μm (X, XI).
Mentions: The later phases of acrosome formation were examined by TEM (Figure 6). In the cap phase in wild-type cells (Figure 6, I), proacrosomal vesicles that had budded from the TGN fused with each other and formed a large acrosome (Ac) located at the acroplaxome (Apx), a unique substructure composed of keratin and actin that serves as a site for anchoring the acrosome to the nuclear membrane (Kierszenbaum et al., 2003). By contrast, in a cap-phase SMAP2-targeted cell (Figure 6, II), acrosomes of intermediate size were formed but never fused to form one large acrosome and remained as multiple pseudoacrosomes (indicated by the arrows). These pseudoacrosomes attached to multiple sites on the nuclear envelope. In another SMAP2-targeted cell (Figure 6, III), one acrosome appeared to be formed but was greatly enlarged in size (the TGN was also disorganized and partly distended; arrows). These observations indicate that acrosome formation from proacrosomal vesicles in SMAP2-deficient cells is disrupted, even though the acroplaxome structures are well organized on the nuclear lamina. Therefore it is unlikely that a defect in the acroplaxome caused the aberrant acrosome formation.

Bottom Line: In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis.Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation.Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Immunology, Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai 980-8575, Japan.

ABSTRACT
The trans-Golgi network (TGN) functions as a hub organelle in the exocytosis of clathrin-coated membrane vesicles, and SMAP2 is an Arf GTPase-activating protein that binds to both clathrin and the clathrin assembly protein (CALM). In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis. Gene targeting reveals that SMAP2-deficient male mice are healthy and survive to adulthood but are infertile and exhibit globozoospermia. In SMAP2-deficient spermatids, the diameter of proacrosomal vesicles budding from TGN increases, TGN structures are distorted, acrosome formation is severely impaired, and reorganization of the nucleus does not proceed properly. CALM functions to regulate vesicle sizes, and this study shows that CALM is not recruited to the TGN in the absence of SMAP2. Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation. Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation. SMAP2-deficient mice provide a model for globozoospermia in humans.

Show MeSH
Related in: MedlinePlus