11 Dec
2013
11 Dec
'13
3:45 p.m.
Dear All,
On Monday 16th December at 12:00 at the PRBB (CRG) Per Ahlberg will give a seminar
entitled:
"Looking in the mirror of evolution: fossils, development and the origin of the jawed
vertebrate face"
Venue: Marie-Curie Room, PRBB
PER AHLBERG, from the Evolutionary Biology Centre at the Uppsala University, Sweden, has
two principal fields of research: Palaeozoic vertebrate evolution with focus on the origin
of tetrapods - the morphological transition from fish to tetrapod - and the relationship
of molecular and developmental patterning to morphological evolution. Specifically he is
looking into the evolution of muscles and bones in vertebrate heads, necks and limbs,
bringing together molecular techniques such as transgenic cell lineage labeling with
palaeontological data in a single analysis. He has been invited by James Sharpe (CRG).
Abstract:
Facial anatomy differs fundamentally between extant jawless and jawed vertebrates
(cyclostomes and gnathostomes). Cyclostomes such as lampreys and hagfishes have a median
nasohypophysial duct; gnathostomes such as zebrafish and humans have separate nasal sacs
opening externally, and a palatal hypophysis. Premandibular neural crest cells migrate
forwards either side of the nasohypophysial placode to form the upper lip in cyclostomes,
but between the hypophysial and nasal placodes to form the trabecular region in
gnathostomes (1). In cyclostomes the forebrain is much shorter than in gnathostomes and
the hypophysis is relatively anterior.
A series of fossils belonging to the gnathostome stem group bridges the gap between these
facial architectures and provides a surprisingly detailed account of the evolutionary and
developmental transformation of the vertebrate face. The most basal of these is the
galeaspid Shuyu, a 430 million year old jawless stem gnathostome (2). Shuyu has a
nasohypophysial duct, short forebrain, and anteriorly oriented hypophysis, but the nasal
sacs and hypophysis are separated by a rudimentary trabecula. The placoderm Romundina, a
415 million year old jawed stem gnathostome, represents a more advanced transitional step.
Its cranial cavity is similar to that of Shuyu, with an anteriorly directed hypophysis and
very short telencephalon. The trabecular region is exceptionally long and wide, with
proportions similar to a cyclostome or galeaspid upper lip, whereas the nasal capsule
(demarcated by a fissure) is small and located far behind the tip of the snout. We
interpret these features as uniquely primitive among jawed vertebrates. In slightly more
advanced placoderms like Dicksonosteus (3), the trabecular region is shortened anteriorly
so that the nasal capsule becomes terminal: a spatialrelationship that is retained in all
later jawed vertebrates.
We suggest that during the evolution of the gnathostome face, separation of the nasal and
hypophysial placodes was followed by loss of the nasohypophysial duct, then by anterior
shortening of the trabecular region which placed the nasal capsules in a rostral position,
and finally by a lengthening of the entire preorbital face (including the forebrain)
without further change in the relative proportions of its components.
(1) Oisi, Y. et al. Nature 493, 175-180 (2012).
(2) Gai, Z. et al. Nature 476, 324-327 (2011).
(3) Goujet, D., Éditions du Centre national de la recherche scientifique, 284 pp (1984).
Dr. James Sharpe
ICREA Research Professor
Acting Coordinator of EMBL-CRG Systems Biology Unit
Tel: +34 93 316 0098
www: Lab<http://www.crg.es/james_sharpe> -
OPT<http://genex.hgu.mrc.ac.uk/OPT> - CRG<http://www.crg.es/> -
Bioptonics<http://www.bioptonics.com/>
EMBL-CRG Systems Biology Unit
Centre for Genomic Regulation (CRG)
Dr. Aiguader, 88
08003 Barcelona
Spain
16 Dec
16 Dec
2:35 a.m.
Dear All,
I'm sorry to announce that this seminar has been postponed until a later date in
2014,
Best wishes,
James.
On Dec 11, 2013, at 3:45 PM, James Sharpe wrote:
Dear All,
On Monday 16th December at 12:00 at the PRBB (CRG) Per Ahlberg will give a seminar
entitled:
"Looking in the mirror of evolution: fossils, development and the origin of the jawed
vertebrate face"
Venue: Marie-Curie Room, PRBB
PER AHLBERG, from the Evolutionary Biology Centre at the Uppsala University, Sweden, has
two principal fields of research: Palaeozoic vertebrate evolution with focus on the origin
of tetrapods - the morphological transition from fish to tetrapod - and the relationship
of molecular and developmental patterning to morphological evolution. Specifically he is
looking into the evolution of muscles and bones in vertebrate heads, necks and limbs,
bringing together molecular techniques such as transgenic cell lineage labeling with
palaeontological data in a single analysis. He has been invited by James Sharpe (CRG).
Abstract:
Facial anatomy differs fundamentally between extant jawless and jawed vertebrates
(cyclostomes and gnathostomes). Cyclostomes such as lampreys and hagfishes have a median
nasohypophysial duct; gnathostomes such as zebrafish and humans have separate nasal sacs
opening externally, and a palatal hypophysis. Premandibular neural crest cells migrate
forwards either side of the nasohypophysial placode to form the upper lip in cyclostomes,
but between the hypophysial and nasal placodes to form the trabecular region in
gnathostomes (1). In cyclostomes the forebrain is much shorter than in gnathostomes and
the hypophysis is relatively anterior.
A series of fossils belonging to the gnathostome stem group bridges the gap between these
facial architectures and provides a surprisingly detailed account of the evolutionary and
developmental transformation of the vertebrate face. The most basal of these is the
galeaspid Shuyu, a 430 million year old jawless stem gnathostome (2). Shuyu has a
nasohypophysial duct, short forebrain, and anteriorly oriented hypophysis, but the nasal
sacs and hypophysis are separated by a rudimentary trabecula. The placoderm Romundina, a
415 million year old jawed stem gnathostome, represents a more advanced transitional step.
Its cranial cavity is similar to that of Shuyu, with an anteriorly directed hypophysis and
very short telencephalon. The trabecular region is exceptionally long and wide, with
proportions similar to a cyclostome or galeaspid upper lip, whereas the nasal capsule
(demarcated by a fissure) is small and located far behind the tip of the snout. We
interpret these features as uniquely primitive among jawed vertebrates. In slightly more
advanced placoderms like Dicksonosteus (3), the trabecular region is shortened anteriorly
so that the nasal capsule becomes terminal: a spatialrelationship that is retained in all
later jawed vertebrates.
We suggest that during the evolution of the gnathostome face, separation of the nasal and
hypophysial placodes was followed by loss of the nasohypophysial duct, then by anterior
shortening of the trabecular region which placed the nasal capsules in a rostral position,
and finally by a lengthening of the entire preorbital face (including the forebrain)
without further change in the relative proportions of its components.
(1) Oisi, Y. et al. Nature 493, 175-180 (2012).
(2) Gai, Z. et al. Nature 476, 324-327 (2011).
(3) Goujet, D., Éditions du Centre national de la recherche scientifique, 284 pp (1984).
Dr. James Sharpe
ICREA Research Professor
Acting Coordinator of EMBL-CRG Systems Biology Unit
Tel: +34 93 316 0098
www: Lab<http://www.crg.es/james_sharpe> -
OPT<http://genex.hgu.mrc.ac.uk/OPT> - CRG<http://www.crg.es/> -
Bioptonics<http://www.bioptonics.com/>
EMBL-CRG Systems Biology Unit
Centre for Genomic Regulation (CRG)
Dr. Aiguader, 88
08003 Barcelona
Spain
Dr. James Sharpe
ICREA Research Professor
Acting Coordinator of EMBL-CRG Systems Biology Unit
Tel: +34 93 316 0098
www: Lab<http://www.crg.es/james_sharpe> -
OPT<http://genex.hgu.mrc.ac.uk/OPT> - CRG<http://www.crg.es/> -
Bioptonics<http://www.bioptonics.com/>
EMBL-CRG Systems Biology Unit
Centre for Genomic Regulation (CRG)
Dr. Aiguader, 88
08003 Barcelona
Spain
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James Sharpe