Marianne Bronner-Fraser

Cancerous stem cells can arise from pediatric brain tumors

Pediatric brain tumors are significant causes of morbidity and mortality. It has been hypothesized that they derive from self-renewing multipotent neural stem cells. Here, we tested whether different pediatric brain tumors, including medulloblastomas and gliomas, contain cells with properties similar to neural stem cells. We find that tumor-derived progenitors form neurospheres that can be passaged at clonal density and are able to self-renew. Under conditions promoting differentiation, individual cells are multipotent, giving rise to both neurons and glia, in proportions that reflect the tumor of origin. Unlike normal neural stem cells, however, tumor-derived progenitors have an unusual capacity to proliferate and sometimes differentiate into abnormal cells with multiple differentiation markers. Gene expression analysis reveals that both whole tumors and tumor-derived neurospheres express many genes characteristic of neural and other stem cells, including CD133, Sox2, musashi-1, bmi-1, maternal embryonic leucine zipper kinase, and phosphoserine phosphatase, with variation from tumor to tumor. After grafting to neonatal rat brains, tumor-derived neurosphere cells migrate, produce neurons and glia, and continue to proliferate for more than 4 weeks. The results show that pediatric brain tumors contain neural stem-like cells with altered characteristics that may contribute to tumorigenesis. This finding may have important implications for treatment by means of specific targeting of stem-like cells within brain tumors.

The amphioxus genome and the evolution of the chordate karyotype.

Lancelets (‘amphioxus’) are the modern survivors of an ancient chordate lineage, with a fossil record dating back to the Cambrian period. Here we describe the structure and gene content of the highly polymorphic ∼520-megabase genome of the Florida lancelet Branchiostoma floridae, and analyse it in the context of chordate evolution. Whole-genome comparisons illuminate the murky relationships among the three chordate groups (tunicates, lancelets and vertebrates), and allow not only reconstruction of the gene complement of the last common chordate ancestor but also partial reconstruction of its genomic organization, as well as a description of two genome-wide duplications and subsequent reorganizations in the vertebrate lineage. These genome-scale events shaped the vertebrate genome and provided additional genetic variation for exploitation during vertebrate evolution.

Epithelial-mesenchymal transitions: the importance of changing cell state in development and disease

The events that convert adherent epithelial cells into individual migratory cells that can invade the extracellular matrix are known collectively as epithelial-mesenchymal transition (EMT). Throughout evolution, the capacity of cells to switch between these two cellular states has been fundamental in the generation of complex body patterns. Here, we review the EMT events that build the embryo and further discuss two prototypical processes governed by EMT in amniotes: gastrulation and neural crest formation. Cells undergo EMT to migrate and colonize distant territories. Not surprisingly, this is also the mechanism used by cancer cells to disperse throughout the body.

A gene regulatory network orchestrates neural crest formation

The neural crest is a multipotent, migratory cell population that is unique to vertebrate embryos and gives rise to many derivatives, ranging from the peripheral nervous system to the craniofacial skeleton and pigment cells. A multimodule gene regulatory network mediates the complex process of neural crest formation, which involves the early induction and maintenance of the precursor pool, emigration of the neural crest progenitors from the neural tube via an epithelial to mesenchymal transition, migration of progenitor cells along distinct pathways and overt differentiation into diverse cell types. Here, we review our current understanding of these processes and discuss the molecular players that are involved in the neural crest gene regulatory network.

Analysis of the Early Stages of Trunk Neural Crest Migration in Avian Embryos Using Monoclonal Antibody HNK-1

The monoclonal antibody HNK-1 was used to identify neural crest cells in serial sections of avian embryos to provide a detailed description of the distribution of trunk neural crest cells. The results indicate the presence of three migratory routes in the trunk: (1) a ventral pathway through the anterior sclerotome; (2) a ventral pathway between the neural tube and the posterior sclerotome; and (3) a dorsolateral pathway between the somites and ectoderm. Neural crest cells were first seen entering the anterior half of the sclerotome at about the time the somite begins to dissociate to form the dermomyotome and sclerotome, approximately 5-10 somites rostral to the most recently formed somite. In contrast, neural crest cells were never observed in the posterior sclerotome or in the perinotochordal space. The distribution of neural crest cells was compared with that of injected latex beads which were previously found to translocate along the ventral trunk neural crest pathway (Bronner-Fraser, Dev. Biol. 91, 130, 1982). During the early stages of neural crest migration, injected latex beads were found to extensively colocalize with cells stained by the HNK-1 antibody. Injected latex beads (78%) were found immediately adjacent to HNK-1 positive cells and another 11% were within one cell diameter. The results suggest that latex beads injected into the trunk somites are deposited onto a normal pathway of neural crest migration.

The amphioxus genome illuminates vertebrate origins and cephalochordate biology

Cephalochordates, urochordates, and vertebrates evolved from a common ancestor over 520 million years ago. To improve our understanding of chordate evolution and the origin of vertebrates, we intensively searched for particular genes, gene families, and conserved noncoding elements in the sequenced genome of the cephalochordate Branchiostoma floridae, commonly called amphioxus or lancelets. Special attention was given to homeobox genes, opsin genes, genes involved in neural crest development, nuclear receptor genes, genes encoding components of the endocrine and immune systems, and conserved cis-regulatory enhancers. The amphioxus genome contains a basic set of chordate genes involved in development and cell signaling, including a fifteenth Hox gene. This set includes many genes that were co-opted in vertebrates for new roles in neural crest development and adaptive immunity. However, where amphioxus has a single gene, vertebrates often have two, three, or four paralogs derived from two whole-genome duplication events. In addition, several transcriptional enhancers are conserved between amphioxus and vertebrates--a very wide phylogenetic distance. In contrast, urochordate genomes have lost many genes, including a diversity of homeobox families and genes involved in steroid hormone function. The amphioxus genome also exhibits derived features, including duplications of opsins and genes proposed to function in innate immunity and endocrine systems. Our results indicate that the amphioxus genome is elemental to an understanding of the biology and evolution of nonchordate deuterostomes, invertebrate chordates, and vertebrates.

Interactions of Eph-related receptors and ligands confer rostrocaudal pattern to trunk neural crest migration

BACKGROUND In the trunk of avian embryos, neural crest migration through the somites is segmental, with neural crest cells entering the rostral half of each somitic sclerotome but avoiding the caudal half. Little is known about the molecular nature of the cues-intrinsic to the somites-that are responsible for this segmental migration of neural crest cells. RESULTS We demonstrate that Eph-related receptor tyrosine kinases and their ligands are essential for the segmental migration of avian trunk neural crest cells through the somites. EphB3 localizes to the rostral half-sclerotome, including the neural crest, and the ligand ephrin-B1 has a complementary pattern of expression in the caudal half-sclerotome. To test the functional significance of this striking asymmetry, soluble ligand ephrin-B1 was added to interfere with receptor function in either whole trunk explants or neural crest cells cultured on alternating stripes of ephrin-B1 versus fibronection. Neural crest cells in vitro avoided migrating on lanes of immobilized ephrin-B1; the addition of soluble ephrin-B1 blocked this inhibition. Similarly, in whole trunk explants, the metameric pattern of neural crest migration was disrupted by addition of soluble ephrin-B1, allowing entry of neural crest cells into caudal portions of the sclerotome. CONCLUSIONS Both in vivo and in vitro, the addition of soluble ephrin-B1 results in a loss of the metameric migratory pattern and a disorganization of neural crest cell movement. These results demonstrate that Eph-family receptor tyrosine kinases and their transmembrane ligands are involved in interactions between neural crest and sclerotomal cells, mediating an inhibitory activity necessary to constrain neural precursors to specific territories in the developing nervous system.

Developmental potential of avian trunk neural crest cells in situ

To analyze the developmental potential of individual neural crest cells or their precursors, we have microinjected a vital dye, lysinated rhodamine dextran (LRD), into single cells in the dorsal neural tube. The phenotypes of the descendants that inherited the LRD from the injected cells were evaluated based upon their position, morphology, and neurofilament expression. Individual neural crest cells labeled before or as they emigrated from the neural tube gave rise to both sensory and sympathetic neurons as well as nonneuronal cells, some of which had the morphological characteristics of Schwann cells or pigment cells. In numerous cases, the descendants of a single cell included both neural crest- and neural tube-derived neurons, suggesting that some cells of the peripheral and central nervous systems share a common lineage. Our data demonstrate definitively that both emigrating and premigratory trunk neural crest cells can be multipotent, giving rise not only to cells in multiple neural crest derivatives, but also to both neuronal and nonneuronal elements within a given derivative.

Induction of the neural crest: a multigene process

In the embryo, the neural crest is an important population of cells that gives rise to diverse derivatives, including the peripheral nervous system and the craniofacial skeleton. Evolutionarily, the neural crest is of interest as an important innovation in vertebrates. Experimentally, it represents an excellent system for studying fundamental developmental processes, such as tissue induction. Classical embryologists have identified interactions between tissues that lead to neural crest formation. More recently, geneticists and molecular biologists have identified the genes that are involved in these interactions; this recent work has revealed that induction of the neural crest is a complex multistep process that involves many genes.

An Antibody to a Receptor for Fibronectin and Laminin Perturbs Cranial Neural Crest Development in Vivo

Previous studies from this laboratory (M. Bronner-Fraser (1985). J. Cell Biol. 101, 610) have demonstrated that an antibody to a cell surface receptor complex caused alterations in avian neural crest cell migration. Here, these observations are extended to examine the distribution and persistency of injected antibody, the dose dependency of the effect, and the long-term influences of antibody injection. The CSAT antibody, which recognizes a cell surface receptor for fibronectin and laminin, was injected lateral to the mesencephalic neural tube at the onset of cranial neural crest migration. Injected antibody molecules did not cross the midline, but appeared to diffuse throughout the injected half of the mesencephalon, where they remained detectable by immunocytochemistry for about 22 hr. Embryos were examined either during neural crest migration (up to 24 hr after injection) or after formation of neural crest-derived structures (36-48 hr after injection). In those embryo fixed within the first 24 hr, the major defects were a reduction in the neural crest cell number on the injected side, a buildup of neural crest cells within the lumen of the neural tube, and ectopically localized neural crest cells. In embryos allowed to survive for 36 to 48 hr after injection, the neural crest derivatives appeared normal on both the injected and control side, suggesting that the embryos compensated for the reduction in neural crest cell number on the injected side. However, the embryos often had severely deformed neural tubes and ectopic aggregates of neural crest cells. In contrast, several control antibodies had no effect. These findings suggest that the CSAT receptor complex is important in the normal development of the neural crest and neural tube.