Society for Developmental Biology meeting summary

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I got back from the Society for Developmental Biology meetings in Calgary last week, and I've put together some summaries of various sessions I attended on Pharyngula. There are digests of the talks on Development and Human Health, Education, Hox genes, Patterning, and Stem Cells, and for the Panda's Thumb crowd, there may be particular interest in the Evo-devo session and my meeting with Paul Nelson of the Discovery Institute.

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Somehow it scares me that Paul is at the same time the best and worst of what encompasses ID.

Somehow it scares me that Paul is at the same time the best and worst of what encompasses ID

He is large, he contains multitudes.….…

Andy, put a little more Intelligent Design behind hitting that post button. Your random process ain’t workin’ out.

;-)

For those who didn’t see what happened and don’t get my joke, the post

Posted by Andy Groves on August 2, 2004 03:29 PM

Somehow it scares me that Paul is at the same time the best and worst of what encompasses ID

He is large, he contains multitudes . … . …

was repeated about 4 times. Then these Stalinist evolutionists went and altered history.

;-)

For some reason, the url is getting mangled and the semicolons are getting messed up. Try this link instead.

Whereas I am a religious person by choice, I do believe there are other explanations to how humans came into existence. I have been studying various theories and came across some interesting “wisdom”. It appears to be a genetic blueprint or fingerprint of the human body… For further inquiry please visit my website @: http://www.geocities.com/scribe6662000

That’s just silly. Look up apophenia sometime.

Nelson has posted a response to PZ over at ISCID here

Interesting paper

Evolution of development in the sea star genus Patiriella: clade-specific alterations in cleavage

Anna Cerra Maria Byrne

Abstract

Examination of early development in five species of the Patiriella sea star species complex indicates that the ancestral-type radial holoblastic cleavage (Type I) is characteristic of P. regularis and P. exigua, whereas cleavage in species from the calcar clade followed multiple alternatives (Types II–IV) from holoblastic to meroblastic. Considering that invariant radial cleavage is thought to play a role in embryonic axis formation in echinoderms, we documented the details of blastomere formation in Patiriella sp. and followed development of the embryos. In Type II cleavage, the first and second cleavage planes appeared simultaneously at one pole of the embryo, dividing it directly into four equally sized blastomeres. In Type III cleavage, the first and second cleavage planes appeared simultaneously, followed promptly by the third cleavage plane, dividing the embryo directly into eight equally sized blastomeres. In Type IV cleavage, numerous furrows appeared simultaneously at one end of the embryo, dividing it into 32–40 equally sized blastomeres. Confocal sections revealed that embryos with cleavage Types II–IV were initially syncytial. The timing of karyokinesis in embryos with Types II and III cleavage was similar to that seen in clutch mates with Type I cleavage. Karyokinesis in embryos with Type IV cleavage, however, differed in timing compared with Type I clutch mates. Alteration in cleavage was not associated with polarized distribution of maternally provided nutrients. For each cleavage type, development was normal to the competent larval stage. Although variable blastomere configuration in the calcar clade may be linked to possession of a lecithotrophic development, other Patiriella species with this mode of development have typical cleavage. The presence of variable cleavage in all calcar clade species indicates that phylogenetic history has played a role in the distribution of this embryonic trait in Patiriella. The plasticity in early cleavage in these sea stars indicates that this aspect of early development is not constrained against change and that there are many ways to achieve multicellularity.

Nelson Wrote:

Reviewing these fundamental differences, Grbic muses, “It is hard to conceptualize the evolution of a novel stage that disrupts one of the crucial paradigms of Drosophila development, maternal specification of the embryonic axis” (Grbic 2003, p. 640).

From the paper

It is hard to conceptualize how is the proliferative stage integrated with de novo establishment of embryonic axes. All 2000 embryo axes appear to form independently with random axial orientation relative to each other (Grbic et al., 1996b). This favours an independent specification of the axial polarity within each embryo rather than a global mechanism specifying simultaneous polarity in 2000 embryos. However, recent genetic analysis of the basal long germband wasp reveals differences relative to fly development that could be utilized to develop the model of evolution of polyembryony. Genetic analysis of the long germ ectoparasitic wasp Nasonia virtripennis revealed mutations in embryo pattern that correspond to putative gap and pair-rule mutant phenotypes in Drosophila, as well as zygotic phenotypes that have no fly mutant counterparts (Pultz et al., 1999). Most importantly, it appears that in Nasonia zygotic control has a more prominent effect on embryo patterning, contrasting predominantly maternal early control as determined in the fly (Pultz et al., 1999). It is hard to conceive that at the stage of embryonic primordium (and during its formation) a Drosophila-like transcription gradient operates in the cellular environment of Copidosoma and Macrocentrus embryos. However, gap genes appear to be involved in embryo patterning in both wasps. It is possible that the predominance of zygotic control of embryo patterning in the ancestral long germband wasps such as Nasonia could be used as a stepping stone to shift embryo patterning to the zygotic genes at the late stages of embryogenesis (following the proliferation) and thus allow “insertion” of the proliferative stage. However, this still does not explain how de novo axial polarity is initiated at the polyembryonic blastoderm. Emerging evolutionary flexibility of early genes involved in polarization of the embryonic axis in insects suggests that it is impossible to use the candidate gene approach based on the Drosophila paradigm to isolate the earliest axial organizers in polyembryonic wasps. The cellular environment in endoparasitic wasps narrows the choice of genes to a group of signaling genes that are used in other systems to establish embryonic axis. Current knowledge of the patterning of polyembryonic and monoembryonic wasps suggests two approaches to isolate putative genes involved in de novo establishment of axial polarity. One approach would be to utilize genomic EST expression screens in both monoembryonic holoblastic cleaving and polyembryonic wasps to isolate those that are expressed at the future embryo poles. In addition, isolation of the regulatory regions of Kruppel could serve as a tool in determining the gene products binding to its regulatory regions in Copidosoma and Macrocentrus. This could provide clues as to how the conserved phase of the gap patterning cascade is integrated with the regulatory elements directing de novo establishment of axial polarity.

Nelson Wrote:

Reviewing these fundamental differences, Grbic muses, “It is hard to conceptualize the evolution of a novel stage that disrupts one of the crucial paradigms of Drosophila development, maternal specification of the embryonic axis” (Grbic 2003, p. 640).

From the paper

It is hard to conceptualize the evolution of a novel stage that disrupts one of the crucial paradigms of Drosophila development, maternal specification of the embryonic axis, while at the same time creating de novo 2000 independent embryonic axes! If the syncytial environment of the Drosophila pre-blastoderm embryo has created complications in understanding how pattern formation proceeds in the cellular milleu of short and intermediate germband insects (Wilkins, 2001), then polyembryonic development represents a real challenge for the Drosophila paradigm. One of first prerequisites for such an event appears to be the uncoupling of posterior patterning and germ cell specification. The second step should include the initiation of the proliferation mechanisms to generate at least 40,000 cells necessary for initiation of 2000 embryonic primordia (Grbic at al. 1998). There are several relatively simple possible means how to initiate proliferation. In the monoembryonic ancestor cleavages must generate enough cells for the formation of the single embryonic primordium. At this point proliferation has to stop and become coupled with axial patterning. Thus, a simple change in the regulatory region of the mitogenic signal could extend the period of proliferation necessary for polyembryonic development. Another avenue generating the same effect would be to produce a mutation in the putative suppressor of proliferation that terminates early proliferation and regulates entry into the blastoderm stage of the monoembryonic ancestor. Both of these changes are relatively simple and could involve existing genes without requiring new gene recruitment Wilkins, 2001). In a likewise manner, removal of the mitogenic signal by a similar mechanism at the completion of proliferation could regulate the exit from the proliferative stage. It is hard to conceptualize how is the proliferative stage integrated with de novo establishment of embryonic axes. All 2000 embryo axes appear to form independently with random axial orientation relative to each other (Grbic et al., 1996b). This favours an independent specification of the axial polarity within each embryo rather than a global mechanism specifying simultaneous polarity in 2000 embryos. However, recent genetic analysis of the basal long germband wasp reveals differences relative to fly development that could be utilized to develop the model of evolution of polyembryony. Genetic analysis of the long germ ectoparasitic wasp Nasonia virtripennis revealed mutations in embryo pattern that correspond to putative gap and pair-rule mutant phenotypes in Drosophila, as well as zygotic phenotypes that have no fly mutant counterparts (Pultz et al., 1999). Most importantly, it appears that in Nasonia zygotic control has a more prominent effect on embryo patterning, contrasting predominantly maternal early control as determined in the fly (Pultz et al., 1999). It is hard to conceive that at the stage of embryonic primordium (and during its formation) a Drosophila-like transcription gradient operates in the cellular environment of Copidosoma and Macrocentrus embryos. However, gap genes appear to be involved in embryo patterning in both wasps. It is possible that the predominance of zygotic control of embryo patterning in the ancestral long germband wasps such as Nasonia could be used as a stepping stone to shift embryo patterning to the zygotic genes at the late stages of embryogenesis (following the proliferation) and thus allow “insertion” of the proliferative stage. However, this still does not explain how de novo axial polarity is initiated at the polyembryonic blastoderm. Emerging evolutionary flexibility of early genes involved in polarization of the embryonic axis in insects suggests that it is impossible to use the candidate gene approach based on the Drosophila paradigm to isolate the earliest axial organizers in polyembryonic wasps. The cellular environment in endoparasitic wasps narrows the choice of genes to a group of signaling genes that are used in other systems to establish embryonic axis. Current knowledge of the patterning of polyembryonic and monoembryonic wasps suggests two approaches to isolate putative genes involved in de novo establishment of axial polarity. One approach would be to utilize genomic EST expression screens in both monoembryonic holoblastic cleaving and polyembryonic wasps to isolate those that are expressed at the future embryo poles. In addition, isolation of the regulatory regions of Kruppel could serve as a tool in determining the gene products binding to its regulatory regions in Copidosoma and Macrocentrus. This could provide clues as to how the conserved phase of the gap patterning cascade is integrated with the regulatory elements directing de novo establishment of axial polarity.

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Would someone who has the ability kindly delete the first of my posts, above? No doubt Andy Groves is relieved to see that he’s not the multiple-posting blog incompetent around…

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This page contains a single entry by PZ Myers published on August 2, 2004 11:14 AM.

Uncommon Dissent II was the previous entry in this blog.

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