Background & History
Following a generous donation, the BSDB has instituted the Dennis Summerbell Lecture, to be delivered at its annual Autumn Meeting by a junior researcher at either PhD or Post-doctoral level. The awardee’s costs for attending the meeting will be met in full.
Dennis Summerbell made seminal contributions to our understanding of limb bud patterning by combining detailed quantitative analysis with elegant models, bringing insightful conceptual advances to the field. In addition to his research, Dennis made major contributions to Developmental Biology through his mentoring of junior researchers. An account of his work can be found on page 10 0f the BSDB Summer Newsletter from 2005 [LINK].
The 2018 lecture awardee was Mariya Dobreva (VIB-KU Leuven Center for Brain & Disease Research and Department of Human Genetics, KU Leuven, Belgium) with her submitted abstract “Amniotic ectoderm expansion in mouse occurs via distinct modes and depends on Smad5-mediated signalling”. Her award lecture was presented at the Autumn Meeting 2018: Embryonic-Extraembryonic Interactions – from genetics to environment, 10-13 September 2018 in Oxford, UK.
Upon gastrulation, the mammalian conceptus transforms rapidly from a simple bilayer into a multi-layered embryo enveloped by its extraembryonic membranes. The embryonic-extraembryonic junction is a hot spot for dynamic cell rearrangements that drive early morphogenesis. The innermost extraembryonic membrane, the amnion, develops at the embryonic-extraembryonic interphase and gradually encases the developing conceptus. Impaired amnion development causes major embryonic malformations, yet its origin remains ill-defined. Mouse embryos, deficient in the BMP signalling effector SMAD5, show aberrant amnion and ventral folding morphogenesis and delayed closure of the proamniotic canal. I developed a microdissection technique and sequenced the transcriptomes of individual Smad5 mutant amnions isolated before the first visible malformations appear (E7.0-E7.5). I revealed two sets of defective amnions: one with a primitive-streak mesoderm signature and another one with unexpected chorionic ectoderm signature. Tetraploid chimera and immunostaining assays indicated that, in both cases, a deficit in the expansion of amniotic ectoderm results in inclusion of non-amniotic, non-squamous tissues in the amniotic microenvironment. Interestingly, the inclusions can be either of embryonic or of extraembryonic origin. To explain the different types of Smad5 mutant defects and to clarify the origin of mouse amnion, we related our findings to existing clonal analysis of early mouse embryos performed by Kirstie A. Lawson (University of Edinburgh). She traced the fate of single cells labeled before amnion formation. Four clone types contribute to the amniotic ectoderm with distinct growth patterns. Two main clone types were identified, with progenitors in the extreme proximal-anterior epiblast. Their early descendants initiate and expand amniotic ectoderm posteriorly, following the progression of the developing amniochorionic fold. Surprisingly, descendants of cells remaining anteriorly, later expand the amniotic ectoderm from its anterior side. The progenitor regions of all types are close to BMP sources in extraembryonic ectoderm and visceral endoderm. We attribute the two Smad5 mutant defect types to impairment of progenitors of the two main cell populations in amniotic ectoderm, and to compromised cuboidal-to-squamous transition of the anterior amniotic ectoderm. In both cases, SMAD5 is critical for expanding the amniotic ectoderm rapidly into a stretchable squamous sheet to accommodate exocoelom expansion, axial growth and folding morphogenesis.
See article: Dobreva et al., 2018, Development 145(15).
- 2018 Mariya Dobreva VIB-KU Leuven Center for Brain & Disease Research and Department of Human Genetics, KU Leuven, Belgium)
- 2017 Helen Weavers (School of Biochemistry, Faculty of Biomedical – [blog post]
- 2016 Iwo Kucinski (Gurdon Institute, University of Cambridge) – [details]
Nominations for the Summerbell Award
Applicants should be BSDB members, have a maximum of 10 years research experience and should not be a principal investigator. To be considered for this award, please send in:
- a 1 page CV
- a paragraph from your PI in support of your application
- abstract for your presentation which should be of relevance to the topic of the Autumn meeting.
Applications should be sent to one of the meeting organisers, and the deadline is usually during the first half of July, as will be announced on our website and in announcements to BSDB members. The nomination will be decided by the meeting organisers