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Neural Blastocyst Complementation: A New Means to Study Brain Development in Mouse

Review of “Neural blastocyst complementation enables mouse forebrain organogenesis” from Nature by Stuart P. Atkinson 

Blastocyst complementation involves the injection of donor embryonic stem cells (ESCs) into mutant blastocysts to contribute to a mutation-associated missing cell lineage. While this technique may allow for the generation of transplantable human organs in large animals, blastocyst complementation also finds use in the functional analysis of genes generally required for development. 

A previous study from Bjoern Schwer (University of California, San Francisco) and Frederick W. Alt (Harvard Medical School, Boston, USA) employed blastocyst complementation to analyze the development of mature lymphocytes in mice [1, 2], while another related report employed this technique for pancreas organogenesis in pigs [3]. Now, the team of Schwer and Alt return with a Nature report that describes neural blastocyst complementation (NBC) as a means to study the development and function of the brain [4].

The newly-described NBC approach generates animals lacking a cerebral cortex and hippocampus by crossing mice carrying a Cre recombinase expression cassette driven by a dorsal telencephalic progenitor-specific promoter (Emx1) with mice carrying a floxed STOP cassette upstream of an attenuated diphtheria toxin subunit A introduced into the Rosa26 locus. The injection of wild-type mouse ESCs into the modified blastocysts acts to “fill the void” left by the progenitors destroyed by targeted toxin expression and, in this study, ESC complementation provided for a chimeric embryo with morphologically and neurologically normal neocortices and hippocampi after gestation in foster females. Importantly, chimeric pups displayed similar learning and memory functions and levels of fertility and longevity as wild-type mice, establishing that NBC performed as anticipated.

However, the authors went further than this “simple” blastocyst complementation and gene-modified ESCs using CRISPR/Cas9 technology before injection into the modified blastocyst to create a faithful model of doublecortin-deficiency, in which mice exhibit disrupted hippocampal lamination. This NBC strategy generated a model with the same characteristics as a model developed via a conventional germline knockout approach [5, 6] suggesting that NBC represents an exciting new means to investigate brain development in the mouse.

While the authors anticipate that NBC will provide a much-needed boost for studies regarding the genes and genomic elements that control cortical and hippocampal development and physiology in mice, they also highlight the general applicability of their ablation strategy to other brain regions and other organ systems.

For more on this novel approach to the study of the development of tissues and organs, stay tuned to the Stem Cells Portal!

References

  1. Chen J, Lansford R, Stewart V, et al., RAG-2-deficient blastocyst complementation: an assay of gene function in lymphocyte development. Proceedings of the National Academy of Sciences 1993;90:4528-32.
  2. Chen J, Gorman JR, Stewart V, et al., Generation of normal lymphocyte populations by <em>Rb</em>-deficient embryonic stem cells. Current Biology 1993;3:405-413.
  3. Matsunari H, Nagashima H, Watanabe M, et al., Blastocyst complementation generates exogenic pancreas in vivo in apancreatic cloned pigs. Proceedings of the National Academy of Sciences 2013;110:4557-62.
  4. Chang AN, Liang Z, Dai H-Q, et al., Neural blastocyst complementation enables mouse forebrain organogenesis. Nature 2018;563:126-130.
  5. Corbo JC, Deuel TA, Long JM, et al., Doublecortin Is Required in Mice for Lamination of the Hippocampus But Not the Neocortex. Journal of Neuroscience 2002;22:7548-7557.
  6. Kappeler C, Dhenain M, Phan Dinh Tuy F, et al., Magnetic resonance imaging and histological studies of corpus callosal and hippocampal abnormalities linked to doublecortin deficiency. Journal of Comparative Neurology 2007;500:239-54.