Extraembryonic Tissue

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Urs Schmidtott - One of the best experts on this subject based on the ideXlab platform.

  • postgastrular zen expression is required to develop distinct amniotic and serosal epithelia in the scuttle fly megaselia
    Developmental Biology, 2010
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Urs Schmidtott
    Abstract:

    The amnioserosa is an Extraembryonic epithelium that evolved in higher cyclorrhaphan flies from distinct serosal and amniotic epithelia. The underlying genetic mechanism of this evolutionary transition is unknown. Amnioserosa development of Drosophila correlates with novel expression characteristics of the homeobox gene zerknullt (zen), including a broad zen expression domain in the syncytial blastoderm and the complete absence of postgastrular zen expression. Here we examine the functional significance of these features by altering the activity profile of zen in Megaselia (a lower cyclorrhaphan fly with distinct serosal and amniotic epithelia) and Drosophila, and by examining in Megaselia the function of u-shaped group (ush-group) genes, which in Drosophila maintain the amnioserosa after gastrulation when zen is no longer expressed. In Megaselia, loss of postgastrular zen expression abrogates serosa development but allows amnion development. Ectopic expression of zen in early Megaselia embryos allows serosa formation but perturbs amnion development. Megaselia homologues of u-shaped group genes are not essential for serosa formation but mediate germband retraction and dorsal closure. Finally, ectopic postgastrular zen expression in Drosophila causes an enlargement of amnioserosa cells and interferes with the morphogenetic functions of the amnioserosa. Our results suggest that the origin of the amnioserosa involved the loss of postgastrular zen expression from Extraembryonic Tissue, that the early broad expression domain of Drosophila zen evolved afterwards, and that the ush-group genes ancestrally played a role in morphogenetic functions of the amnion.

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Abstract Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen. Megaselia Episyrphus Drosophila EvoDevo homology

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen.

J. Samarut - One of the best experts on this subject based on the ideXlab platform.

  • The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic Tissue
    Retrovirology, 2012
    Co-Authors: A. Mey, H. Acloque, Emmanuelle Lerat, S. Gounel, V. Tribollet, S. Blanc, D. Curton, A-m. Birot, M Angela Nieto, J. Samarut
    Abstract:

    Background: Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and Extraembryonic lineages. To assess the transcriptional contribution of ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells. Results: We show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward Extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors' activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog and Gata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an Extraembryonic Tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1. Conclusion: Our results show that Ens-1 LTR have co-opted conditions required for the emergence of Extraembryonic Tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and Extraembryonic fates.

  • The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic Tissue
    Retrovirology, 2012
    Co-Authors: A. Mey, H. Acloque, Emmanuelle Lerat, S. Gounel, V. Tribollet, S. Blanc, D. Curton, A-m. Birot, A. Nieto, J. Samarut
    Abstract:

    Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and Extraembryonic lineages. To assess the transcriptional contributionof ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells. We show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward Extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors’ activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog andGata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an Extraembryonic Tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1.Our results show that Ens-1 LTR have co-opted conditions required for the emergence of Extraembryonic Tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and Extraembryonic fates.

Ab Matteen Rafiqi - One of the best experts on this subject based on the ideXlab platform.

  • postgastrular zen expression is required to develop distinct amniotic and serosal epithelia in the scuttle fly megaselia
    Developmental Biology, 2010
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Urs Schmidtott
    Abstract:

    The amnioserosa is an Extraembryonic epithelium that evolved in higher cyclorrhaphan flies from distinct serosal and amniotic epithelia. The underlying genetic mechanism of this evolutionary transition is unknown. Amnioserosa development of Drosophila correlates with novel expression characteristics of the homeobox gene zerknullt (zen), including a broad zen expression domain in the syncytial blastoderm and the complete absence of postgastrular zen expression. Here we examine the functional significance of these features by altering the activity profile of zen in Megaselia (a lower cyclorrhaphan fly with distinct serosal and amniotic epithelia) and Drosophila, and by examining in Megaselia the function of u-shaped group (ush-group) genes, which in Drosophila maintain the amnioserosa after gastrulation when zen is no longer expressed. In Megaselia, loss of postgastrular zen expression abrogates serosa development but allows amnion development. Ectopic expression of zen in early Megaselia embryos allows serosa formation but perturbs amnion development. Megaselia homologues of u-shaped group genes are not essential for serosa formation but mediate germband retraction and dorsal closure. Finally, ectopic postgastrular zen expression in Drosophila causes an enlargement of amnioserosa cells and interferes with the morphogenetic functions of the amnioserosa. Our results suggest that the origin of the amnioserosa involved the loss of postgastrular zen expression from Extraembryonic Tissue, that the early broad expression domain of Drosophila zen evolved afterwards, and that the ush-group genes ancestrally played a role in morphogenetic functions of the amnion.

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Abstract Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen. Megaselia Episyrphus Drosophila EvoDevo homology

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen.

A. Mey - One of the best experts on this subject based on the ideXlab platform.

  • The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic Tissue
    Retrovirology, 2012
    Co-Authors: A. Mey, H. Acloque, Emmanuelle Lerat, S. Gounel, V. Tribollet, S. Blanc, D. Curton, A-m. Birot, M Angela Nieto, J. Samarut
    Abstract:

    Background: Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and Extraembryonic lineages. To assess the transcriptional contribution of ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells. Results: We show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward Extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors' activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog and Gata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an Extraembryonic Tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1. Conclusion: Our results show that Ens-1 LTR have co-opted conditions required for the emergence of Extraembryonic Tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and Extraembryonic fates.

  • The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic Tissue
    Retrovirology, 2012
    Co-Authors: A. Mey, H. Acloque, Emmanuelle Lerat, S. Gounel, V. Tribollet, S. Blanc, D. Curton, A-m. Birot, A. Nieto, J. Samarut
    Abstract:

    Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and Extraembryonic lineages. To assess the transcriptional contributionof ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells. We show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward Extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors’ activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog andGata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an Extraembryonic Tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1.Our results show that Ens-1 LTR have co-opted conditions required for the emergence of Extraembryonic Tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and Extraembryonic fates.

Steffen Lemke - One of the best experts on this subject based on the ideXlab platform.

  • postgastrular zen expression is required to develop distinct amniotic and serosal epithelia in the scuttle fly megaselia
    Developmental Biology, 2010
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Urs Schmidtott
    Abstract:

    The amnioserosa is an Extraembryonic epithelium that evolved in higher cyclorrhaphan flies from distinct serosal and amniotic epithelia. The underlying genetic mechanism of this evolutionary transition is unknown. Amnioserosa development of Drosophila correlates with novel expression characteristics of the homeobox gene zerknullt (zen), including a broad zen expression domain in the syncytial blastoderm and the complete absence of postgastrular zen expression. Here we examine the functional significance of these features by altering the activity profile of zen in Megaselia (a lower cyclorrhaphan fly with distinct serosal and amniotic epithelia) and Drosophila, and by examining in Megaselia the function of u-shaped group (ush-group) genes, which in Drosophila maintain the amnioserosa after gastrulation when zen is no longer expressed. In Megaselia, loss of postgastrular zen expression abrogates serosa development but allows amnion development. Ectopic expression of zen in early Megaselia embryos allows serosa formation but perturbs amnion development. Megaselia homologues of u-shaped group genes are not essential for serosa formation but mediate germband retraction and dorsal closure. Finally, ectopic postgastrular zen expression in Drosophila causes an enlargement of amnioserosa cells and interferes with the morphogenetic functions of the amnioserosa. Our results suggest that the origin of the amnioserosa involved the loss of postgastrular zen expression from Extraembryonic Tissue, that the early broad expression domain of Drosophila zen evolved afterwards, and that the ush-group genes ancestrally played a role in morphogenetic functions of the amnion.

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Abstract Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen. Megaselia Episyrphus Drosophila EvoDevo homology

  • evolutionary origin of the amnioserosa in cyclorrhaphan flies correlates with spatial and temporal expression changes of zen
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Ab Matteen Rafiqi, Steffen Lemke, Sean Ferguson, Michael Stauber, Urs Schmidtott
    Abstract:

    Higher cyclorrhaphan flies including Drosophila develop a single Extraembryonic epithelium (amnioserosa), which closes the germband dorsally. In most other insects two Extraembryonic epithelia, serosa and amnion, line the inner eggshell and the ventral germband, respectively. How the two Extraembryonic epithelia evolved into one is unclear. Recent studies have shown that, in the flour beetle Tribolium and in the milkweed bug Oncopeltus, the homeobox gene zerknullt (zen) controls the fusion of the amnion with the serosa before dorsal closure. To understand the origin of the amnioserosa in evolution, we examined the expression and function of zen in the Extraembryonic Tissue of lower Cyclorrhapha. We show that Megaselia abdita (Phoridae) and Episyrphus balteatus (Syrphidae) develop a serosa and a dorsal amnion, suggesting that a dorsal amnion preceded the origin of the amnioserosa in evolution. Using Kruppel (Kr) and pannier (pnr) homologues of Megaselia as markers for serosal and amniotic Tissue, respectively, we show that after zen RNAi all Extraembryonic Tissue becomes indistinguishable from amniotic cells, like in Tribolium but unlike in Drosophila, in which zen controls all aspects of Extraembryonic development. Compared with Megaselia and Episyrphus, zen expression in Drosophila is extended to cells that form the amnion in lower Cyclorrhapha and is down-regulated at the developmental stage, when serosa cells in lower Cyclorrhapha begin to expand. These expression differences between species with distinct Extraembryonic Tissue organizations and the conserved requirement of zen for serosa development suggest that the origin of an amnioserosa-like epithelium was accompanied by expression changes of zen.

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