Limits...
Integrins on eggs: focal adhesion kinase is activated at fertilization, forms a complex with integrins, and is necessary for cortex formation and cell cycle initiation.

Chan D, Thomas CJ, Taylor VJ, Burke RD - Mol. Biol. Cell (2013)

Bottom Line: Cyclin E normally accumulates in the nucleus 15 min after fertilization, then returns to background levels.PF573 228- or Y11-treated eggs accumulate cyclin E in the nucleus; however, levels remain high.In addition, PF573 228 interferes with the accumulation of pERK1/2 in the nucleus and in eggs initiating mitosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC V8P 5C2, Canada.

ABSTRACT
We investigate the proposal that integrins and focal adhesion kinase (FAK) form a complex that has structural and signaling functions in eggs. FAK protein is present in eggs and is phosphorylated at fertilization. pY(397)FAK localizes to the membrane 30 min after fertilization, which correlates with the expression of βC integrins and egg cortex development. The βC integrin and pY(397)FAK coimmunoprecipitate from egg cortex lysates. PF573 228 and Y11, inhibitors of FAK, interfere with pronuclear fusion and reduce the abundance of pY(397)FAK and cortical actin without affecting microvillar actin. Cyclin E normally accumulates in the nucleus 15 min after fertilization, then returns to background levels. PF573 228- or Y11-treated eggs accumulate cyclin E in the nucleus; however, levels remain high. In addition, PF573 228 interferes with the accumulation of pERK1/2 in the nucleus and in eggs initiating mitosis. Injection of eggs with a fusion protein consisting of the focal adhesion-targeting domain of FAK fused to green fluorescent protein interferes with cortex formation and produces abnormal nuclei. These data indicate that an integrin-FAK adhesion complex forms at the egg surface that functions in formation of actin arrays in the egg cortex and provides signaling inputs for cell cycle initiation.

Show MeSH

Related in: MedlinePlus

Summary of the roles of FAK after fertilization in sea urchin eggs. FAK is present in the cytoplasm and is phosphorylated immediately after fertilization. This activation appears to be necessary for the fusion of male and female pronuclei, and FAK has inputs into the MAP kinase regulation of the reinitiation of the cell cycle. Activation of FAK appears to be necessary for nuclearization of ERK and down-regulation of cyclin E. About 15 min after fertilization, βC integrins are expressed and bind Sp-Del in the extracellular hyaline layer. pFAK is recruited to an integrin-containing complex at the cell surface, where it appears necessary for the elaboration of the cytoplasmic arrays of cortical actin and regulation of phosphorylation of myosin.
© Copyright Policy - creative-commons
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3814141&req=5

Figure 9: Summary of the roles of FAK after fertilization in sea urchin eggs. FAK is present in the cytoplasm and is phosphorylated immediately after fertilization. This activation appears to be necessary for the fusion of male and female pronuclei, and FAK has inputs into the MAP kinase regulation of the reinitiation of the cell cycle. Activation of FAK appears to be necessary for nuclearization of ERK and down-regulation of cyclin E. About 15 min after fertilization, βC integrins are expressed and bind Sp-Del in the extracellular hyaline layer. pFAK is recruited to an integrin-containing complex at the cell surface, where it appears necessary for the elaboration of the cytoplasmic arrays of cortical actin and regulation of phosphorylation of myosin.

Mentions: Our data confirm that FAK protein is present in the egg (Garcia et al., 2004) and demonstrate that it is phosphorylated at Y397 while in the cytoplasm within the first 5 min of development. This immediate response to fertilization suggests that FAK may have a role in early developmental events. Treating eggs with FAK inhibitors during the interval that FAK is cytoplasmic interferes with pronuclear fusion and alters the pattern of nuclear accumulation of cyclin E. There are detailed studies of the mechanisms underlying the reinitiation of the cell cycle in urchin eggs (Philipova et al., 2005; Kisielewska et al., 2009). Kisielewska et al. (2009) demonstrated that Ca2+ activation of ERK1 promotes the coordinate accumulation of GFP-cyclin E and GFP-cdk2 in the egg pronucleus. In addition, their data indicate that cdk2 activity downstream of ERK1 activation is necessary for the initiation of S-phase and DNA synthesis. Philipova et al. (2005) note that inhibition of ERK1 prevents chromatin decondensation of the sperm chromatin after pronuclear fusion. Our data suggest that FAK may have input into this pathway (Figure 9). It is important to note, however, that the effect of blocking FAK with PF573 228 is distinctive, in that it blocks fusion of the male pronucleus, not only decondensation as reported by Philipova et al. (2005). It is also important to note that the FAK inhibitors do not block nuclear accumulation of cyclin E; they appear to interfere with the phasic nature of the increase. Treatment with either inhibitor causes an accumulation through the first 90 min of development. This pattern is distinctive from the pattern of nuclear cyclin E seen with inhibitors of MEK or cdk. Thus our data indicate that during the first 15 min after fertilization, FAK has input into pronuclear fusion, enhances nuclearization of pERK, and is necessary for down-regulation of nuclear cyclin E (Figure 9).


Integrins on eggs: focal adhesion kinase is activated at fertilization, forms a complex with integrins, and is necessary for cortex formation and cell cycle initiation.

Chan D, Thomas CJ, Taylor VJ, Burke RD - Mol. Biol. Cell (2013)

Summary of the roles of FAK after fertilization in sea urchin eggs. FAK is present in the cytoplasm and is phosphorylated immediately after fertilization. This activation appears to be necessary for the fusion of male and female pronuclei, and FAK has inputs into the MAP kinase regulation of the reinitiation of the cell cycle. Activation of FAK appears to be necessary for nuclearization of ERK and down-regulation of cyclin E. About 15 min after fertilization, βC integrins are expressed and bind Sp-Del in the extracellular hyaline layer. pFAK is recruited to an integrin-containing complex at the cell surface, where it appears necessary for the elaboration of the cytoplasmic arrays of cortical actin and regulation of phosphorylation of myosin.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814141&req=5

Figure 9: Summary of the roles of FAK after fertilization in sea urchin eggs. FAK is present in the cytoplasm and is phosphorylated immediately after fertilization. This activation appears to be necessary for the fusion of male and female pronuclei, and FAK has inputs into the MAP kinase regulation of the reinitiation of the cell cycle. Activation of FAK appears to be necessary for nuclearization of ERK and down-regulation of cyclin E. About 15 min after fertilization, βC integrins are expressed and bind Sp-Del in the extracellular hyaline layer. pFAK is recruited to an integrin-containing complex at the cell surface, where it appears necessary for the elaboration of the cytoplasmic arrays of cortical actin and regulation of phosphorylation of myosin.
Mentions: Our data confirm that FAK protein is present in the egg (Garcia et al., 2004) and demonstrate that it is phosphorylated at Y397 while in the cytoplasm within the first 5 min of development. This immediate response to fertilization suggests that FAK may have a role in early developmental events. Treating eggs with FAK inhibitors during the interval that FAK is cytoplasmic interferes with pronuclear fusion and alters the pattern of nuclear accumulation of cyclin E. There are detailed studies of the mechanisms underlying the reinitiation of the cell cycle in urchin eggs (Philipova et al., 2005; Kisielewska et al., 2009). Kisielewska et al. (2009) demonstrated that Ca2+ activation of ERK1 promotes the coordinate accumulation of GFP-cyclin E and GFP-cdk2 in the egg pronucleus. In addition, their data indicate that cdk2 activity downstream of ERK1 activation is necessary for the initiation of S-phase and DNA synthesis. Philipova et al. (2005) note that inhibition of ERK1 prevents chromatin decondensation of the sperm chromatin after pronuclear fusion. Our data suggest that FAK may have input into this pathway (Figure 9). It is important to note, however, that the effect of blocking FAK with PF573 228 is distinctive, in that it blocks fusion of the male pronucleus, not only decondensation as reported by Philipova et al. (2005). It is also important to note that the FAK inhibitors do not block nuclear accumulation of cyclin E; they appear to interfere with the phasic nature of the increase. Treatment with either inhibitor causes an accumulation through the first 90 min of development. This pattern is distinctive from the pattern of nuclear cyclin E seen with inhibitors of MEK or cdk. Thus our data indicate that during the first 15 min after fertilization, FAK has input into pronuclear fusion, enhances nuclearization of pERK, and is necessary for down-regulation of nuclear cyclin E (Figure 9).

Bottom Line: Cyclin E normally accumulates in the nucleus 15 min after fertilization, then returns to background levels.PF573 228- or Y11-treated eggs accumulate cyclin E in the nucleus; however, levels remain high.In addition, PF573 228 interferes with the accumulation of pERK1/2 in the nucleus and in eggs initiating mitosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC V8P 5C2, Canada.

ABSTRACT
We investigate the proposal that integrins and focal adhesion kinase (FAK) form a complex that has structural and signaling functions in eggs. FAK protein is present in eggs and is phosphorylated at fertilization. pY(397)FAK localizes to the membrane 30 min after fertilization, which correlates with the expression of βC integrins and egg cortex development. The βC integrin and pY(397)FAK coimmunoprecipitate from egg cortex lysates. PF573 228 and Y11, inhibitors of FAK, interfere with pronuclear fusion and reduce the abundance of pY(397)FAK and cortical actin without affecting microvillar actin. Cyclin E normally accumulates in the nucleus 15 min after fertilization, then returns to background levels. PF573 228- or Y11-treated eggs accumulate cyclin E in the nucleus; however, levels remain high. In addition, PF573 228 interferes with the accumulation of pERK1/2 in the nucleus and in eggs initiating mitosis. Injection of eggs with a fusion protein consisting of the focal adhesion-targeting domain of FAK fused to green fluorescent protein interferes with cortex formation and produces abnormal nuclei. These data indicate that an integrin-FAK adhesion complex forms at the egg surface that functions in formation of actin arrays in the egg cortex and provides signaling inputs for cell cycle initiation.

Show MeSH
Related in: MedlinePlus