Biomedical subjects

Yoshiakira Kanai

Publications and source records attributed to Yoshiakira Kanai.

At least 19 recordsLinked to original sources

PubMed2006

Potency of testicular somatic environment to support spermatogenesis in XX/Sry transgenic male mice.

The sex-determining region of Chr Y (Sry) gene is sufficient to induce testis formation and the subsequent male development of internal and external genitalia in chromosomally female mice and humans. In XX sex-reversed males, such as XX/Sry-transgenic (XX/Sry) mice, however, testicular germ cells always disappear soon after birth because of germ cell-autonomous defects. Therefore, it remains unclear whether or not Sry alone is sufficient to induce a fully functional testicular soma capable of supporting complete spermatogenesis in the XX body. Here, we demonstrate that the testicular somatic environment of XX/Sry males is defective in supporting the later phases of spermatogenesis. Spermatogonial transplantation analyses using XX/Sry male mice revealed that donor XY spermatogonia are capable of proliferating, of entering meiosis and of differentiating to the round-spermatid stage. XY-donor-derived round spermatids, however, were frequently detached from the XX/Sry seminiferous epithelia and underwent cell death, resulting in severe deficiency of elongated spermatid stages. By contrast, immature XY seminiferous tubule segments transplanted under XX/Sry testis capsules clearly displayed proper differentiation into elongated spermatids in the transplanted XY-donor tubules. Microarray analysis of seminiferous tubules isolated from XX/Sry testes confirmed the missing expression of several Y-linked genes and the alterations in the expression profile of genes associated with spermiogenesis. Therefore, our findings indicate dysfunction of the somatic tubule components, probably Sertoli cells, of XX/Sry testes, highlighting the idea that Sry alone is insufficient to induce a fully functional Sertoli cell in XX mice.

Animals↗

PubMed2006

Identification of Sox17 as a transcription factor that regulates oligodendrocyte development.

Microarray analysis of oligodendrocyte lineage cells purified by fluorescence-activated cell sorting (FACS) from 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-enhanced green fluorescent protein (EGFP) transgenic mice revealed Sox17 (SRY-box containing gene 17) gene expression to be coordinately regulated with that of four myelin genes during postnatal development. In CNP-EGFP-positive (CNP-EGFP+) cells, Sox17 mRNA and protein levels transiently increased between postnatal days 2 and 15, with white matter O4+ preoligodendrocytes expressing greater Sox17 levels than Nkx2.2+ (NK2 transcription factor related, locus 2) NG2+, or GalC+ (galactocerebroside) cells. In spinal cord, Sox17 protein expression was undetectable in the primary motor neuron domain between embryonic days 12.5 and 15.5 but was evident in Nkx2.2+ and CC1+ cells. In cultured oligodendrocyte progenitor cells (OPCs), Sox17 levels were maximal in O4+ cells and peaked during the phenotypic conversion from bipolar to multipolar. Parallel increases in Sox17 and p27 occurred before MBP protein expression, and Sox17 upregulation was prevented by conditions inhibiting differentiation. Sox17 downregulation with small interfering RNAs increased OPC proliferation and decreased lineage progression after mitogen withdrawal, whereas Sox17 overexpression in the presence of mitogen had opposite effects. Sox17 overexpression enhanced myelin gene expression in OPCs and directly stimulated MBP gene promoter activity. These findings support important roles for Sox17 in controlling both oligodendrocyte progenitor cell cycle exit and differentiation.

Animals↗

PubMed2006

Redundant roles of Sox17 and Sox18 in postnatal angiogenesis in mice.

Sox7, Sox17 and Sox18 constitute group F of the Sox family of HMG box transcription factor genes. Dominant-negative mutations in Sox18 underlie the cardiovascular defects observed in ragged mutant mice. By contrast, Sox18(-/-) mice are viable and fertile, and display no appreciable anomaly in their vasculature, suggesting functional compensation by the two other SoxF genes. Here, we provide direct evidence for redundant function of Sox17 and Sox18 in postnatal neovascularization by generating Sox17(+/-) -Sox18(-/-) double mutant mice. Whereas Sox18(-/-) and Sox17(+/-) -Sox18(+/-) mice showed no vascular defects, approximately half of the Sox17(+/-) -Sox18(-/-) pups died before postnatal day 21 (P21). They showed reduced neovascularization in the liver sinusoids and kidney outer medulla vasa recta at P7, which most likely caused the ischemic necrosis observed by P14 in hepatocytes and renal tubular epithelia. Those that survived to adulthood showed similar, but milder, vascular anomalies in both liver and kidney, and females were infertile with varying degrees of vascular abnormalities in the reproductive organs. These anomalies corresponded with sites of expression of Sox7 and Sox17 in the developing postnatal vasculature. In vitro angiogenesis assays, using primary endothelial cells isolated from the P7 livers, showed that the Sox17(+/-) -Sox18(-/-) endothelial cells were defective in endothelial sprouting and remodeling of the vasculature in a phenotype-dependent manner. Therefore, our findings indicate that Sox17 and Sox18, and possibly all three SoxF genes, are cooperatively involved in mammalian vascular development.

Animals↗

PubMed2006

Expression pattern of alphavbeta3 and alphavbeta5 integrin mRNA in mouse fetal gonads.

The alphavbeta3 and alphavbeta5 integrins are known as transmembrane receptors capable of binding to the RGD amino acid peptide sequence. In mouse early gonadogenesis, some proteins containing the RGD sequence are deposited into extracellular space and participate in morphogenesis. We analyzed the expression patterns of the alphavbeta3 and alphavbeta5 integrins in mouse developing gonads (10.5-13.5 days post coitum) using whole-mount in situ hybridization. The alphav integrin mRNA was homogenously expressed in developing gonadal regions. On the other hand, the beta3 integrin mRNA was found only in large and round cells (presumptive germ cells), whereas beta5 integrin was localized in gonadal somatic cells, with the exception of coelomic epithelial cells. The beta3 integrin-expressed cells were determined to be primordial germ cells because the number of these cells was drastically reduced in busulfan-treated gonads. In this study, we demonstrated that the alphavbeta3 and alphavbeta5 integrins are widely localized in the mouse developing gonads and discussed their presumptive functions on mouse gonadogenesis.

Animals↗

PubMed2006

Crucial role of the small GTPase ARF6 in hepatic cord formation during liver development.

The mammalian small GTPase ADP-ribosylation factor 6 (ARF6) plays important roles in a wide variety of cellular events, including endocytosis, actin cytoskeletal reorganization, and phosphoinositide metabolism. However, physiological functions for ARF6 have not previously been examined. Here, we described the consequence of ARF6 ablation in mice, which manifests most obviously in the context of liver development. Livers from ARF6-/- embryos are smaller and exhibit hypocellularity, due to the onset of midgestational liver cell apoptosis. Preceding the apoptosis, however, defective hepatic cord formation is observed; the liver cells migrate abnormally upon exiting the primordial hepatic epithelial sheet and clump rather than becoming dispersed. Consistent with this observation, the ability of hepatocyte growth factor/scatter factor (HGF) to induce hepatic cord-like structures from ARF6-/- fetal hepatocytes cultured in vitro in collagen gel matrix is impaired. Finally, we show that endogenous ARF6 in wild-type fetal hepatocytes is activated in response to HGF stimulation. These results provide evidence that ARF6 is an essential component in the signaling pathway coupling HGF signaling to hepatic cord formation.

ADP-Ribosylation Factor 6↗

PubMed2005

Crucial transcription factors in endoderm and embryonic gut development are expressed in gut-like structures from mouse ES cells.

Mouse embryonic stem (ES) cells are pluripotent and retain the potential to form an organ similar to the gut showing spontaneous contractions in vitro. The morphological features of these structures and their formation, as assessed using the hanging drop method to produce embryoid bodies (EBs), seem to be similar to those in vivo. To determine whether the same molecular mechanisms are involved in the formation process, the expression pattern of transcription factors regulating endoderm and gut development in the mouse embryo was examined by in situ hybridization and compared with in vivo expression. Expression of gene products was also examined by immunohistochemistry, and expression colocalization was analyzed with double staining. The results showed that all factors examined, that is, Sox17, Id2, HNF3beta/Foxa2, and GATA4, were expressed in both EBs and gut-like structures. Moreover, their expression patterns were similar to those in the mouse embryo. EBs after the hanging drop period and before outgrowth already expressed all factors that were colocalized with each other in EB epithelial structures. These findings suggest that the origin of the gut-like structure is determined during the hanging drop period and that the gut-like structure is formed as the epithelial structure in EBs during the hanging drop period. They also indicate that the in vitro system using mouse ES cells mimics in vivo development and should prove useful in the study of molecular mechanisms for endoderm and gut development.

Animals↗

PubMed2005

Adhesion activity of fetal gonadal cells to EGF and discoidin domains of milk fat globule-EGF factor 8 (MFG-E8), a secreted integrin-binding protein which is transiently expressed in mouse early gonadogenesis.

MFG-E8, a secreted integrin-binding protein, consists of two EGF domains containing a RGD motif and two discoidin domains. In mouse embryogenesis, MFG-E8 is highly expressed in gonadal stromal cells near mesonephros at 11.5-12.5 dpc, but its function in gonadogenesis has not been characterized. To clarify a possible role of MFG-E8 in developing gonads, we analyzed the adhesion activity of 10.5-15.5 dpc gonadal cells to recombinant proteins of EGF or discoidin domains of MFG-E8. In EGF-coated wells, the gonadal cells at 11.5-12.5 dpc revealed a significantly higher adhesion activity as compared to those at 10.5 and 15.5 dpc, while discoidin domains showed a constant number of the adhered cells throughout these stages. To identify the adhesive cells of 11.5-dpc gonads, immunohistochemistry with anti-SF1/Ad4Bp antibody (a specific marker for supporting, steroidogenic, and coelomic epithelial cells) and staining for alkaline phosphatase (a germ cell marker) were carried out. As a result, EGF domains, as well as discoidin domains, were capable of binding to all three groups of SF1/Ad4Bp-positive and negative somatic cells, and germ cells of 11.5-dpc gonads. These findings therefore suggest that MFG-E8 mediates the cell-to-cell interaction among several somatic cell types and germ cells in mouse early gonadogenesis.

Animals↗

PubMed2005

A novel Sry-downstream cellular event which preserves the readily available energy source of glycogen in mouse sex differentiation.

Sry is transiently activated in pre-Sertoli cells of the gonadal ridge to initiate testis differentiation in mice. In pre-Sertoli cells, however, the cellular events induced immediately after the onset of Sry expression remain largely unknown. Here we show that testis-specific glycogen accumulation in pre-Sertoli cells is one of the earliest cellular events downstream of Sry action. In developing XY gonads, glycogen accumulation starts to occur in pre-Sertoli cells from around 11.15 dpc (tail somite 14 stage) in a center-to-pole pattern similar to the initial Sry expression profile. Glycogen accumulation was also found in XX male gonads of Sry-transgenic embryos, but not in XX female gonads of wildtype embryos at any developmental stage. In vitro analyses using various culture conditions suggest that testis-specific glycogen deposition is a tissue-autonomous event that can be induced even in serum-free conditions and in a culture of gonadal explants without adjacent mesonephros. Moreover, glycogen accumulation in pre-Sertoli cells was significantly inhibited in vitro by the PI3K inhibitor LY294002, but not by the MEK inhibitor PD98059. Active phospho-AKT (PI3K effector) showed a high degree of accumulation in gonadal somatic cells of genital ridges in a testis-specific manner, both in vitro and in vivo. Therefore, these findings suggest that immediately after the onset of Sry expression, activation of the PI3K-AKT pathway promotes testis-specific glycogen storage in pre-Sertoli cells. To the best of our knowledge, this is a novel Sry-downstream cellular event which preserves this readily available energy source in Sertoli cells for testis-specific morphogenesis and hormone production.

Animals↗

PubMed2005

Influence on spatiotemporal patterns of a male-specific Sox9 activation by ectopic Sry expression during early phases of testis differentiation in mice.

Testis induction is associated with gonadal Sry and Sox9 expression in mammals. This study investigated whether Sry expression directly induces male-specific Sox9 activation during early phases of testis differentiation. We have established an XX sex-reversal mouse line carrying the Sry transgene driven by a weak basal promoter of the Hsp70.3 gene (Hsp-Sry), whereby the transgene was activated in the gonads along the entire anteroposterior axis from earlier stages. The effects of misexpression and overexpression of Sry on the spatiotemporal pattern of Sox9 expression were examined using both XX and XY gonads of Hsp-Sry transgenic embryos. It was shown that ectopic expression of Sry transcripts in the entire gonadal area from earlier stages promotes neither any advance in the timing nor any appreciable ectopic activation of endogenous Sox9 expression. Immediately after the onset of Sox9 activation, however, both the level of Sox9 expression and the number of SOX9-positive cells were significantly enhanced in Hsp-Sry/XY gonads, as compared with those in wild-type/XY and Hsp-Sry/XX gonads. These findings suggest that, although Sry is capable of up-regulating Sox9 expression dose-dependently, Sry mRNA expression alone is not likely to provide positional or timing information needed for male-specific Sox9 activation in developing XY gonads.

Animals↗

PubMed2005

From SRY to SOX9: mammalian testis differentiation.

Sry (sex-determining region on the Y chromosome) is a master gene that initiates testis differentiation of the bipotential indifferent gonad in mammals. In mice, Sry expression is transiently activated in a center-to-pole wave along the anteroposterior (AP) axis of developing XY gonads. Shortly after the onset of Sry activation, Sox9 (Sry-related HMG box-9), a fundamental testis-differentiation gene common to all vertebrates, is also activated in a center-to-pole pattern similar to the initial Sry expression profile. Several male-specific cellular events, such as glycogenesis, coelomic epithelium proliferation, mesonephric migration and vasculogenesis, are induced in XY gonads following the onset of Sry and Sox9 expression. This paper mainly focuses on recent advances in elucidating the regulatory mechanisms of Sry and Sox9 expression and male-specific cellular events immediately downstream of SRY action during the initial phases of testis differentiation.

Animals↗

PubMed2004

Conditional activation of RhoA suppresses the epithelial to mesenchymal transition at the primitive streak during mouse gastrulation.

Gastrulation is a pivotal event of mouse early embryogenesis. In telencephalin (TLCN)-Cre mice carrying the Cre recombinase gene inserted into the translational initiation site of the TLCN gene, Cre-mediated recombination took place at the postimplantation stage. To examine the role of RhoA signaling in early embryogenesis, we produced Rho36 mice carrying constitutively active RhoA(G14V) gene inducible by Cre recombinase and crossed with TLCN-Cre mice. In doubly transgenic embryos at the gastrulation stage, there appeared an abnormal bulge of cells protruded from the primitive streak region into the amniotic cavity. The bulged cell mass expressed the epiblast marker gene Oct3 and E-cadherin, but not the primitive streak marker gene T except for the basal portion. These results suggest that the conditional activation of RhoA signaling suppressed the epithelial to mesenchymal transition at the primitive streak during mouse gastrulation.

Allantois↗

PubMed2004

Effects of trichostatin a, a histone deacetylase inhibitor, on mouse gonadal development in vitro.

Sry, Sox9 and M33 are thought to act as architectural transcription factors or as a chromatin regulator in gonadal development. However, the direct relationship between chromatin structure and sex determination has not yet been revealed. To clarify the effect of chromatin structural change on gonadal development, we examined the effects of trichostatin A, a histone deacetylase inhibitor, on mouse gonadal development in vitro. In the 0.1 microM treated testicular explants, the size of the gonad was significantly decreased, although the testicular cord formation occurred normally. In the 1.0 microM treated explants, the gonads revealed one or two large testicular cords. Sox9 and MIS expressions suggest that Sertoli cell differentiation is induced normally within the testicular cord, while Dnmt3b expression suggests that several immature Sertoli cells are located on the outside of the testicular cord. The 3beta-hsd expression indicates that Leydig cell differentiation occurs normally. On the other hand, germ cell loss was observed in the treated testicular explants. In the treated ovarian explants, the number of premeiotic germ cells was reduced without gonadal size change. Thus, trichostatin A affects the development of germ cells, but does not affect sex determination.

Animals↗

PubMed2004

Expression of Prnp mRNA (prion protein gene) in mouse spermatogenic cells.

The Prnp (prion protein) gene, which encodes a soluble protein anchored to the cell surface by glycosylphosphatidylinositol (GPI), might be involved in cell-to-cell interaction. The expression of Prnp is strongly observed not only in the brain, but also in non-neuronal tissues. In order to examine the Prnp expression sites in mouse testes, we carried out Northern blot and in situ hybridization analyses. By Northern blot analysis, two kinds of Prnp transcripts (major band of 2.2 kb, and minor band of 1.1 kb) were detected in testes. The 2.2-kb transcript was observed in testes throughout the postnatal development, whereas the 1.1-kb transcript was observed in testes from 2 to 70 weeks old. In situ hybridization analysis showed that the positive signals for Prnp mRNAs were predominantly observed in spermatogenic cells, but not in somatic cells such as Sertoli cells, Leydig cells and peritubular myoid cells. The signals were observed moderately in spermatogonia, and strongly in spermatocytes and round spermatids, but not in elongate spermatids and spermatozoa. These results suggest that Prnp may be involved in germ cell differentiation during mammalian spermatogenesis.

Amyloid↗

PubMed2004

A close correlation in the expression patterns of Af-6 and Usp9x in Sertoli and granulosa cells of mouse testis and ovary.

Usp9x, an X-linked deubiquitylating enzyme, is stage dependently expressed in the supporting cells (i.e. Sertoli cells and granulosa cells) and germ cells during mouse gametogenesis. Af-6, a cell junction protein, has been identified as a substrate of Usp9x, suggesting a possible association between Usp9x and Af-6 in spermatogenesis and oogenesis. In this study, we examined the expression pattern of Af-6 and Usp9x and their intracellular localization in testes and ovaries of mice treated with or without pregnant mare serum gonadotropin (PMSG), an FSH-like hormone. In both testes and ovaries, Af-6 expression was predominantly observed in supporting cells, as well as in steroidogenic cells, but not in any germ cells. In Sertoli cells, Af-6 was continuously expressed throughout postnatal and adult stages, where both Af-6 and Usp9x were enriched at the sites of Sertoli-Sertoli and Sertoli-spermatid junctions especially at stages XI-VI. In the granulosa cells, Af-6, as well as Usp9x, was highly expressed in primordial and primary follicles, but its expression rapidly decreased after the late-secondary follicle stage. Interestingly, in PMSG-treated mice, the expression levels of Af-6 and Usp9x were synchronously enhanced, slightly in Sertoli cells and strongly in granulosa cells of the late-secondary and Graafian follicles. Such closely correlated expression patterns between Af-6 and Usp9x clearly suggest that Af-6 may be deubiquitylated by Usp9x in both Sertoli and granulosa cells. It further suggests that the post-translational regulation of Af-6 by Usp9x may be one potential pathway to control the cell adhesion dynamics in mammalian gametogenesis.

Animals↗

PubMed2004

Effects of mono(2-ethylhexyl) phthalate (MEHP) on testes in rats in vitro.

The phthalate esters have been used as plasticizers for various plastic products, and their testicular toxicity has been reported. In this study, the effects of mono(2-ethylhexyl) phthalate (MEHP), one of the phthalate esters, on prepubertal rat testes in vitro were examined. The testes of 20-day-old Sprague Dawley (SD) rats were cut into smaller pieces and seeded in medium, and then the specimens were obtained for light and transmission electron microscopic observations. As a result, at 1 hr after exposure to MEHP, TUNEL-positive spermatogenic cells were identified, and they gradually increased in number in time- and dose-dependent manners. Ultrastructurally, apoptotic spermatogenic cells (characterized with chromatin condensation, cytoplasm shrinkage without membrane rupture, still-functioning cell organelles, and packed cell contents in membrane-bounded bodies), necrotic spermatogenic cells (characterized with swollen and ruptured mitochondria, plasma membrane lysis, spilt cell contents, and chromatin clumps), apoptotic Sertoli cells (highly condensed nuclei and nuclear membrane lysis) and necrotic Sertoli cells (marginated chromatins along the nuclear membrane, some swollen and ruptured cell organelles, e.g. mitochondria) could be identified. Conclusively, based on transmission electron microscopic observations, MEHP treatment may affect spermatogenic cells, and lead them to necrosis. Thus, testicular tissue cultures and cell cultures are of advantageous for screening testicular toxicity of chemicals.

Animals↗

PubMed2004

Postnatal development of multivesicular nuclear body in the Shiba goat Sertoli cell: an ultrastructural study.

The multivesicular nuclear body (MNB) within the Sertoli cell nucleolus has been observed in the ruminant testis, but not in other mammalian species. Generally, the MNB is composed of vesicles, tubules and ribosome-like structures. This study has been conducted in order to clarify MNB formation during postnatal development. The testes were obtained from immature Shiba goats at 1, 2, 3, 4, and 5 months old, and from adults. They were fixed with 5% glutaraldehyde, postfixed with 1% OsO4, dehydrated in ethanol and embedded in Araldite-M. The serial cross-sections of seminiferous tubules were morphologically and morphometrically observed using light and transmission electron microscopy. In these Shiba goat testes, the MNB contained vesicles and tubules in various sizes, as well as ribosome-like structures. The volume of each Sertoli cell nucleus at each age (1, 2, 3, 4, 5 months old and adult) was about 269.3 microm3, 327.1 microm3, 361.3 microm3, 431.2 microm3, 525.0 microm3, and 760.4 microm3, respectively. The average number of vesicles per Sertoli cell nucleus was 0, 7.4, 11.1, 12.3, 15.5, and 32.7, respectively. At 1 month old, one or more nucleoli with fibrillar components were identified in the Sertoli cell nucleus. No MNB was observed. At 2 months old, a MNB first appeared, though it was underdeveloped and infrequently encountered. At this stage, a MNB, consisting of a small amount of vesicles and ribosomes, was located in the peripheral region of the nucleus. At later stages (3, 4, and 5 months old), MNBs gradually developed, increased in number, moved from the periphery to the central region of the nucleus, and associated with the nucleus to form a well-developed MNB. In the adults, the Sertoli cell nucleus displayed a well-developed and large-sized MNB situated in the central region.

Animals↗

PubMed2004

An ultrastructural study on cytotoxic effects of mono(2-ethylhexyl) phthalate (MEHP) on testes in Shiba goat in vitro.

In this study, the effects of mono(2-ethylhexyl) phthalate (MEHP), one of metabolites of di(2-ethylhexyl) phthalate, on immature Shiba goat testes in vitro were examined. The testes of 2-month-old Shiba goats were cut into smaller pieces, and seeded in medium. At 1, 3, 6 and 9 hr after administration of MEHP at various concentrations (0, 100 nmol ml(-1), 1 nmol ml(-1), and 1 x 10(-3) nmol ml(-1), respectively), the specimens were obtained for light and transmission electron microscopic observations. As a result, at 1 hr after exposure to MEHP, the vacuolization and nuclear membrane rupture appeared in Sertoli cells. Such alterations tended to gradually increase in number in time and dose-dependent manners. Moreover, by MEHP treatment, apoptotic spermatogenic cells (characterized with chromatin condensation, cytoplasm shrinkage without membrane rupture, still functioning cell organelles, and packed cell contents in membrane-bounded bodies), apoptotic Sertoli cells (characterized with nuclear membrane lysis, nuclear condensation), necrotic spermatogenic cells (characterized with swollen and ruptured mitochondria, plasma membrane lysis, spilt cell contents, and chromatin clumps), and necrotic Sertoli cells (characterized with marginated chromatins along the nuclear membrane, ruptured vesicles within the MNB, some swollen and ruptured cell organelles, e.g. mitochondria) could be identified. Conclusively, ultrastructurally the treatment with MEHP at low concentration tends to lead spermatogenic and Sertoli cells to apoptosis, whereas that at high concentration tends to lead spermatogenic and Sertoli cells to necrosis. Thus, the testicular tissue culture is advantageous for screening testicular toxicity of chemicals.

Animals↗

PubMed2003

Cofilin phosphorylation and actin polymerization by NRK/NESK, a member of the germinal center kinase family.

Nck-interacting kinase (NIK)-related kinase (NRK)/NIK-like embryo-specific kinase (NESK) is a protein kinase that belongs to the germinal center kinase family, and activates the c-Jun N-terminal kinase (JNK) signaling pathway. In this study, we examined the effect of NRK/NESK on actin cytoskeletal organization. Overexpression of NRK/NESK in COS7 cells induced accumulation of polymerized actin at the perinuclear. Phosphorylation of cofilin, an actin-depolymerizing factor, was increased in NRK/NESK-expressing HEK 293T cells. In addition, in vitro phosphorylation of cofilin was observed on NRK/NESK immunoprecipitates from HEK 293T cells expressing the kinase domain of NRK/NESK. The cofilin phosphorylation occurred at the serine residue of position 3 (Ser-3). Since the phosphorylation at Ser-3 inactivates the actin-depolymerizing activity of cofilin, these results suggest that NRK/NESK induces actin polymerization through cofilin phosphorylation. The cofilin phosphorylation did not appear to be mediated through activation of LIM-kinasel, a cofilin-phosphorylating kinase, or through the activation of JNK. Thus, cofilin is likely to be a direct substrate of NRK/NESK. NRK/NESK is predominantly expressed in skeletal muscle during the late stages of mouse embryogenesis. Thus, NRK/NESK may be involved in the regulation of actin cytoskeletal organization in skeletal muscle cells through cofilin phosphorylation.

Actin Depolymerizing Factors↗