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ABSTRACT: The ventricular zone (VZ) of the embryonic dorsal telencephalon is a major site for generating cortical projection neurons. The transcription factor Pax6 is highly expressed in apical progenitors (APs) residing in the VZ from the earliest stages of corticogenesis. Previous studies mainly focused on Pax6(-/-) mice have implicated Pax6 in regulating cortical progenitor proliferation, neurogenesis, and formation of superficial cortical layers. We analyzed the developing cortex of PAX77 transgenic mice that overexpress Pax6 in its normal domains of expression. We show that Pax6 overexpression increases cell cycle length of APs and drives the system toward neurogenesis. These effects are specific to late stages of corticogenesis, when superficial layer neurons are normally generated, in cortical regions that express Pax6 at the highest levels. The number of superficial layer neurons is reduced in postnatal PAX77 mice, whereas radial migration and lamina specification of cortical neurons are not affected by Pax6 overexpression. Conditional deletion of Pax6 in cortical progenitors at midstages of corticogenesis, by using a tamoxifen-inducible Emx1-CreER line, affected both numbers and specification of late-born neurons in superficial layers of the mutant cortex. Our analyses suggest that correct levels of Pax6 are essential for normal production of superficial layers of the cortex.
Cerebral Cortex 04/2010; 21(1):81-94. · 6.54 Impact Factor
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ABSTRACT: Foxg1 is required for development of the ventral telencephalon in the embryonic mammalian forebrain. Although one existing hypothesis suggests that failed ventral telencephalic development in the absence of Foxg1 is due to reduced production of the morphogens sonic hedgehog (Shh) and fibroblast growth factor 8 (Fgf8), the possibility that telencephalic cells lacking Foxg1 are intrinsically incompetent to generate the ventral telencephalon has remained untested. We examined the ability of Foxg1(-/-) telencephalic cells to respond to Shh and Fgf8 by examining the expression of genes whose activation requires Shh or Fgf8 in vivo and by testing their responses to Shh and Fgf8 in culture. We found that many elements of the Shh and Fgf8 signalling pathways continue to function in the absence of Foxg1 but, nevertheless, we were unable to elicit normal responses of key ventral telencephalic marker genes in Foxg1(-/-) telencephalic tissue following a range of in vivo and in vitro manipulations. We explored the development of Foxg1(-/-) cells in Foxg1(-/-) Foxg1(+/+) chimeric embryos that contained ventral telencephalon created by normally patterned wild-type cells. We found that Foxg1(-/-) cells contributed to the chimeric ventral telencephalon, but that they retained abnormal specification, expressing dorsal rather than ventral telencephalic markers. These findings indicate that, in addition to regulating the production of ventralising signals, Foxg1 acts cell-autonomously in the telencephalon to ensure that cells develop the competence to adopt ventral identities.
Development 02/2010; 137(3):487-97. · 6.60 Impact Factor
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ABSTRACT: The transcription factor Pax6 is expressed by many cell types in the developing eye. Eyes do not form in homozygous loss-of-function mouse mutants (Pax6Sey/Sey) and are abnormally small in Pax6Sey/+ mutants. Eyes are also abnormally small in PAX77 mice expressing multiple copies of human PAX6 in addition to endogenous Pax6; protein sequences are identical in the two species. The developmental events that lead to microphthalmia in PAX77 mice are not well-characterised, so it is not clear whether over- and under-expression of Pax6/PAX6 cause microphthalmia through similar mechanisms. Here, we examined the consequences of over-expression for the eye and its axonal connections.
Eyes form in PAX77+/+ embryos but subsequently degenerate. At E12.5, we found no abnormalities in ocular morphology, retinal cell cycle parameters and the incidence of retinal cell death. From E14.5 on, we observed malformations of the optic disc. From E16.5 into postnatal life there is progressively more severe retinal dysplasia and microphthalmia. Analyses of patterns of gene expression indicated that PAX77+/+ retinae produce a normal range of cell types, including retinal ganglion cells (RGCs). At E14.5 and E16.5, quantitative RT-PCR with probes for a range of molecules associated with retinal development showed only one significant change: a slight reduction in levels of mRNA encoding the secreted morphogen Shh at E16.5. At E16.5, tract-tracing with carbocyanine dyes in PAX77+/+ embryos revealed errors in intraretinal navigation by RGC axons, a decrease in the number of RGC axons reaching the thalamus and an increase in the proportion of ipsilateral projections among those RGC axons that do reach the thalamus. A survey of embryos with different Pax6/PAX6 gene dosage (Pax6Sey/+, Pax6+/+, PAX77+ and PAX77+/+) showed that (1) the total number of RGC axons projected by the retina and (2) the proportions that are sorted into the ipsilateral and contralateral optic tracts at the optic chiasm vary differently with gene dosage. Increasing dosage increases the proportion projecting ipsilaterally regardless of the size of the total projection.
Pax6 overexpression does not obviously impair the initial formation of the eye and its major cell-types but prevents normal development of the retina from about E14.5, leading eventually to severe retinal degeneration in postnatal life. This sequence is different to that underlying microphthalmia in Pax6+/- heterozygotes, which is due primarily to defects in the initial stages of lens formation. Before the onset of severe retinal dysplasia, Pax6 overexpression causes defects of retinal axons, preventing their normal growth and navigation through the optic chiasm.
BMC Developmental Biology 02/2008; 8:59. · 2.79 Impact Factor
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Martine Manuel,
Petrina A Georgala,
Catherine B Carr,
Simon Chanas,
Dirk A Kleinjan,
Ben Martynoga,
John O Mason,
Michael Molinek,
Jeni Pinson,
Thomas Pratt,
Jane C Quinn,
T Ian Simpson,
David A Tyas,
Veronica van Heyningen,
John D West,
David J Price
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ABSTRACT: Levels of expression of the transcription factor Pax6 vary throughout corticogenesis in a rostro-lateral(high) to caudo-medial(low) gradient across the cortical proliferative zone. Previous loss-of-function studies have indicated that Pax6 is required for normal cortical progenitor proliferation, neuronal differentiation, cortical lamination and cortical arealization, but whether and how its level of expression affects its function is unclear. We studied the developing cortex of PAX77 YAC transgenic mice carrying several copies of the human PAX6 locus with its full complement of regulatory regions. We found that PAX77 embryos express Pax6 in a normal spatial pattern, with levels up to three times higher than wild type. By crossing PAX77 mice with a new YAC transgenic line that reports Pax6 expression (DTy54), we showed that increased expression is limited by negative autoregulation. Increased expression reduces proliferation of late cortical progenitors specifically, and analysis of PAX77<---->wild-type chimeras indicates that the defect is cell autonomous. We analyzed cortical arealization in PAX77 mice and found that, whereas the loss of Pax6 shifts caudal cortical areas rostrally, Pax6 overexpression at levels predicted to shift rostral areas caudally has very little effect. These findings indicate that Pax6 levels are stabilized by autoregulation, that the proliferation of cortical progenitors is sensitive to altered Pax6 levels and that cortical arealization is not.
Development 03/2007; 134(3):545-55. · 6.60 Impact Factor
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ABSTRACT: Pax6 is a highly conserved transcription factor essential for the development of the eyes in vertebrate and invertebrate species. It is also required for normal development of many regions of the central nervous system, including the mammalian forebrain, hindbrain and spinal cord. In the forebrain, it is expressed in a gradient in the dorsal telencephalon, where it is required for the expression of genes that confer dorsal characteristics and where it might play a role in regionalization of the cerebral cortex. It is expressed in the diencephalon, where it is essential for the specification of its derivatives. While the ancestral function of Pax6 may have been to specify a structure sensitive to light, it has been co-opted into the regulation of a broader range of processes in development of the vertebrate nervous system.
Brain Research Bulletin 10/2005; 66(4-6):387-93. · 2.82 Impact Factor
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Marko Kallio,
Yunhua Chang, Martine Manuel,
Tero-Pekka Alastalo,
Murielle Rallu,
Yorick Gitton,
Lila Pirkkala,
Marie-Thérèse Loones,
Liliana Paslaru,
Severine Larney,
Sophie Hiard,
Michel Morange,
Lea Sistonen,
Valérie Mezger
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ABSTRACT: Heat shock factor 2, one of the four vertebrate HSFs, transcriptional regulators of heat shock gene expression, is active during embryogenesis and spermatogenesis, with unknown functions and targets. By disrupting the Hsf2 gene, we show that, although the lack of HSF2 is not embryonic lethal, Hsf2(-/-) mice suffer from brain abnormalities, and meiotic and gameto genesis defects in both genders. The disturbances in brain are characterized by the enlargement of lateral and third ventricles and the reduction of hippocampus and striatum, in correlation with HSF2 expression in proliferative cells of the neuroepithelium and in some ependymal cells in adults. Many developing spermatocytes are eliminated via apoptosis in a stage-specific manner in Hsf2(-/-) males, and pachytene spermatocytes also display structural defects in the synaptonemal complexes between homologous chromosomes. Hsf2(-/-) females suffer from multiple fertility defects: the production of abnormal eggs, the reduction in ovarian follicle number and the presence of hemorrhagic cystic follicles are consistent with meiotic defects. Hsf2(-/-) females also display hormone response defects, that can be rescued by superovulation treatment, and exhibit abnormal rates of luteinizing hormone receptor mRNAs.
The EMBO Journal 07/2002; 21(11):2591-601. · 9.20 Impact Factor
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Marko Kallio,
Yunhua Chang, Martine Manuel,
Tero-Pekka Alastalo,
Murielle Rallu,
Yorick Gitton,
Lila Pirkkala,
Marie-Th|[eacute]|r|[egrave]|se Loones,
Liliana Paslaru,
Severine Larney,
Sophie Hiard,
Michel Morange,
Lea Sistonen,
Val|[eacute]|rie Mezger
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ABSTRACT: Heat shock factor 2, one of the four vertebrate HSFs, transcriptional regulators of heat shock gene expression, is active during embryogenesis and spermatogenesis, with unknown functions and targets. By disrupting the Hsf2 gene, we show that, although the lack of HSF2 is not embryonic lethal, Hsf2-/- mice suffer from brain abnormalities, and meiotic and gameto genesis defects in both genders. The disturbances in brain are characterized by the enlargement of lateral and third ventricles and the reduction of hippocampus and striatum, in correlation with HSF2 expression in proliferative cells of the neuroepithelium and in some ependymal cells in adults. Many developing spermatocytes are eliminated via apoptosis in a stage-specific manner in Hsf2-/- males, and pachytene spermatocytes also display structural defects in the synaptonemal complexes between homologous chromosomes. Hsf2-/- females suffer from multiple fertility defects: the production of abnormal eggs, the reduction in ovarian follicle number and the presence of hemorrhagic cystic follicles are consistent with meiotic defects. Hsf2-/- females also display hormone response defects, that can be rescued by superovulation treatment, and exhibit abnormal rates of luteinizing hormone receptor mRNAs.
The EMBO Journal 06/2002; 21(11):2591-2601. · 9.20 Impact Factor
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ABSTRACT: Heat shock transcription factors (HSFs) are characterized by their ability, upon activation, to bind to heat shock response elements (HSE) present in the promoter of their target genes. HSE are composed of inverted repeats of the pentamer nGAAm. In this study, we compare the embryonic HSF2 protein, purified from F9 embryonal carcinoma cells tumor, and the in vitro synthesized HSF2. We show that the context of HSF2 synthesis influences its thermosensitivity and DNA-binding properties. Therefore, we determined the consensus binding sequence for the purified embryonic HSF2 by the technique of systematic evolution of ligands by exponential enrichment (SELEX). We show that embryonic HSF2 prefers sites containing three or four nGAAm inverted pentamers and that its optimal binding sequence contains the 8-mer palindromic core 5'-TTCTAGAA-3'. The consensus binding sequence for the embryonic HSF2 will be very helpful to identify new targets for this factor, during developmental and differentiation processes.
European Journal of Biochemistry 06/2002; 269(10):2527-37. · 3.58 Impact Factor
