With the ultimate goal of understanding how genetic modules have evolved in the telencephalon, we set out to modernize the functional analysis of cross-species cis-regulatory elements in mouse. In utero electroporation is rapidly replacing transgenesis as the method of choice for gain- and loss-of-function studies in the murine telencephalon, but the application of this technique to the analysis of transcriptional regulation has yet to be fully explored and exploited. To empirically define the developmental stages required to target specific populations of neurons in the dorsal telencephalon, or pallium, which gives rise to the neocortex in mouse, we performed a temporal and spatial analysis of the migratory properties of electroporated versus birth-dated cells. Next, we compared the activities of two known Ngn2 enhancers via transgenesis and in utero electroporation, demonstrating that the latter technique more faithfully reports the endogenous telencephalic expression pattern observed in an Ngn2lacZ knock-in line. Finally, we used this approach to test the telencephalic activities of a series of deletion constructs comprised of the zebrafish ER81 upstream regulatory region, allowing us to identify a previously uncharacterized enhancer that displays cross-species activity in the murine piriform cortex and lateral neocortex, yet not in more medial domains of the forebrain. Taken together, our data supports the contention that in utero technology can be exploited to rapidly examine the architecture and evolution of pallial-specific cis-regulatory elements.
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"Because the netrin-1/DCC signaling axis is important for corpus callosum formation (Izzi and Charron, 2011; Fothergill et al., 2014), we next examined the role of Hsc70 on netrin-1–de- pendent axonal projections in vivo. Embryonic telencephalons were transfected with pCIG2 vectors expressing GFP alone or GFP along with Hsc70 or Hsc70 D10N by in utero electroporation at E14.5, when cortical progenitors exclusively generate upper layer commissural projection neurons (Langevin et al., 2007). After electroporation, embryos were left to develop for 3 d in utero before collection and processing. "
[Show abstract][Hide abstract] ABSTRACT: During development, netrin-1 is both an attractive and repulsive axon guidance cue and mediates its attractive function through the receptor Deleted in Colorectal Cancer (DCC). The activation of Rho guanosine triphosphatases within the extending growth cone facilitates the dynamic reorganization of the cytoskeleton required to drive axon extension. The Rac1 guanine nucleotide exchange factor (GEF) Trio is essential for netrin-1–induced axon outgrowth and guidance. Here, we identify the molecular chaperone heat shock cognate protein 70 (Hsc70) as a novel Trio regulator. Hsc70 dynamically associated with the N-terminal region and Rac1 GEF domain of Trio. Whereas Hsc70 expression supported Trio-dependent Rac1 activation, adenosine triphosphatase–deficient Hsc70 (D10N) abrogated Trio Rac1 GEF activity and netrin-1–induced Rac1 activation. Hsc70 was required for netrin-1–mediated axon growth and attraction in vitro, whereas Hsc70 activity supported callosal projections and radial neuronal migration in the embryonic neocortex. These findings demonstrate that Hsc70 chaperone activity is required for Rac1 activation by Trio and this function underlies
netrin-1/DCC-dependent axon outgrowth and guidance.
Full-text · Article · Aug 2015 · The Journal of Cell Biology
"brain sections (96 ± 36 and 18 ± 7). Considering that expression of detectable levels of EGFP is restricted to cells born shortly after in utero electroporation was performed (36) these observations suggest that the Thy1.2→hGFAP Co-Driver pair targeted reporter gene activation mainly to cells that were born later relative to the tdTomato+ cells observed as a result of hGFAP→Thy1.2 "
[Show abstract][Hide abstract] ABSTRACT: Conditional mutagenesis using Cre recombinase expressed from tissue specific promoters facilitates analyses of gene function
and cell lineage tracing. Here, we describe two novel dual-promoter-driven conditional mutagenesis systems designed for greater
accuracy and optimal efficiency of recombination. Co-Driver employs a recombinase cascade of Dre and Dre-respondent Cre, which
processes loxP-flanked alleles only when both recombinases are expressed in a predetermined temporal sequence. This unique
property makes Co-Driver ideal for sequential lineage tracing studies aimed at unraveling the relationships between cellular
precursors and mature cell types. Co-InCre was designed for highly efficient intersectional conditional transgenesis. It relies
on highly active trans-splicing inteins and promoters with simultaneous transcriptional activity to reconstitute Cre recombinase
from two inactive precursor fragments. By generating native Cre, Co-InCre attains recombination rates that exceed all other
binary SSR systems evaluated in this study. Both Co-Driver and Co-InCre significantly extend the utility of existing Cre-responsive
Full-text · Article · Jan 2014 · Nucleic Acids Research
"In utero electroporation was performed on pregnant CD-1 mice at E13 according to published protocols (Langevin et al., 2007; Saito and Nakatsuji, 2001). Embryos were collected at 20 hours, 48 hours and 5 days following in utero electroporation, or 2 weeks postnatal. "
[Show abstract][Hide abstract] ABSTRACT: Cortical development requires the precise timing of neural precursor cell (NPC) terminal mitosis. Although cell cycle proteins regulate terminal mitosis, the factors that influence the cell cycle machinery are incompletely understood. Here we show in mice that myeloid cell leukemia 1 (Mcl1), an anti-apoptotic Bcl-2 protein required for the survival of NPCs, also regulates their terminal differentiation through the cell cycle regulator p27(Kip1). A BrdU-Ki67 cell profiling assay revealed that in utero electroporation of Mcl1 into NPCs in the embryonic neocortex increased NPC cell cycle exit (the leaving fraction). This was further supported by a decrease in proliferating NPCs (Pax6(+) radial glial cells and Tbr2(+) neural progenitors) and an increase in differentiating cells (Dcx(+) neuroblasts and Tbr1(+) neurons). Similarly, BrdU birth dating demonstrated that Mcl1 promotes premature NPC terminal mitosis giving rise to neurons of the deeper cortical layers, confirming their earlier birthdate. Changes in Mcl1 expression within NPCs caused concomitant changes in the levels of p27(Kip1) protein, a key regulator of NPC differentiation. Furthermore, in the absence of p27(Kip1), Mcl1 failed to induce NPC cell cycle exit, demonstrating that p27(Kip1) is required for Mcl1-mediated NPC terminal mitosis. In summary, we have identified a novel physiological role for anti-apoptotic Mcl1 in regulating NPC terminal differentiation.