NF-κB and Snail1a coordinate the cell cycle with gastrulation

Abstract

The cell cycle needs to strictly coordinate with developmental processes to ensure correct generation of the body plan and different tissues. However, the molecular mechanism underlying the coordination remains largely unknown. In this study, we investigate how the cell cycle coordinates gastrulation cell movements in zebrafish. We present a system to modulate the cell cycle in early zebrafish embryos by manipulating the geminin-Cdt1 balance. Alterations of the cell cycle change the apoptotic level during gastrulation, which correlates with the nuclear level of antiapoptotic nuclear factor κB (NF-κB). NF-κB associates with the Snail1a promoter region on the chromatin and directly activates Snail1a, an important factor controlling cell delamination, which is the initial step of mesendodermal cell movements during gastrulation. In effect, the cell cycle coordinates the delamination of mesendodermal cells through the transcription of Snail1a. Our results suggest a molecular mechanism by which NF-κB and Snail1a coordinate the cell cycle through gastrulation.

A high-sensitivity bi-directional reporter to monitor NF-κB activity in cell culture and zebrafish in real time

“…The GFP expression seen with the pSGNluc reporter in the first 30 hpf is consistent with previously described early expression of NF-κB transcription factors (Correa et al, 2004) and reflected published spatiotemporal expression patterns of genes involved in NF-κB signaling at these stages, such as c-rel (Correa et al, 2004) and ikk1 (Correa et al, 2005). This early NF-κB activation matches what is known about the functional requirements for NF-κB signaling during embryogenesis: during gastrulation NF-κB activation is involved in coordinating the cell cycle and mesoendodermal cell movements (Liu et al, 2009) and lack of NF-κB signaling in the notochord leads to embryonic dorsalization and deformities (Correa et al, 2004). The requirement of finely tuned NF-κB signaling during notochord differentiation is also supported by the defects caused by high doses of iκbαa morpholino.…”

Snail1 suppresses TGF-β-induced apoptosis and is sufficient to trigger EMT in hepatocytes

“…This confirms the connection between NF-B and Snail upregulation described in several cell lines (Barberá et al, 2004; Snail1 overcomes TGF--induced apoptosis Julien et al, 2007;Kim et al, 2007) and during development , and it is reminiscent of the recently described binding of p65 to the snail1a promoter in zebrafish embryos (Liu et al, 2009). Interestingly, other intracellular signals appear to be dispensable, such as MEK/ERKs or PI3-K.…”

Geminin Is Required for Epithelial to Mesenchymal Transition at Gastrulation

“…The striking lack of Geminin in the epidermal ectoderm suggests that Geminin may function in the ectoderm like other preneural genes, such as Sox3 and Zic2 that are required for the induction of neural tissue by BMP inhibition, thereby positioning the neural-epidermal ectodermal border [54,73], consistent with observations that overexpression increases and reductions in Geminin reduce the size of the neural plate in Xenopus [7], Zebrafish [49], and Drosophila [10] embryos. Geminin may then maintain proliferation in the neural ectoderm and prevent premature expression of genes involved in faterestriction [34,35,74].…”

“…Geminin mutant embryos exhibit body wall closure defects after failure of morphogenetic movements and endoderm differentiation, as previously reported in Zebrafish [49]. Lack of normal anterior mesendoderm migration also resulted in the failure of DE to replace PE, and persistent signaling in the anterior region, identified by expanded Cer1 and Hesx1 expression, which likely have long-term effects on patterning of the anterior central nervous system (CNS) [50].…”

“…The Geminin gastrulation phenotype in KD embryos is also similar to mouse embryos lacking Hira [43], Fgfr1 [44,45], Fgf8 [46], the Nodal target Eomesodermin [47], and Snail1 [48], where cells fail to leave the primitive streak. Exposure of Zebrafish embryos to Geminin morpholinos similarly repressed Snail1a; mesendodermal cells did not delaminate, while overexpression promoted Snail1a production and endodermal differentiation [49], suggesting that Geminin plays a central, critical role in this cascade.…”