Our Science – Lewandoski Website
Mark B. Lewandoski, Ph.D.
The mission of my laboratory is to study the role of embryonic induction during normal development. Embryonic development and cancer can be viewed as flip sides of the same coin. During embryogenesis, signal transduction pathways result in basic cell behaviors such as programmed cell death, proliferation, migration and differentiation. During oncogenesis, these same signal transduction cascades are misinterpreted, pathologically reactivated or ignored, resulting in aberrant cellular behaviors. Thus, understanding the normal role of signal transduction during development is extremely valuable in understanding cancer and ultimately will provide necessary insights for intervening with effective cancer therapies.
We have initially focused on studying fibroblast growth factors (FGFs) because they exemplify this type of signal transduction molecule: they often play an essential role in a variety of organizing centers that pattern the embryo and are also important in the growth of certain human tumors. For example, much of our work directly or indirectly concerns Fgf8, which was first cloned as an androgen-induced protein in mammary cancer cells, and plays a key role in prostate cancer. As Fgf8, plays no known role in the adult its normal function can only be studied during embryogenesis.
Our main methodology is to study the perturbation of development in embryos that carry loss-of-function alleles. We often use conditional alleles that are subject to Cre-mediated regulation in order to bypass early requirements for given gene products as many genes play different roles at different stages of development. This approach also provides precise control over gene expression in specific tissues - allowing us to address questions heretofore unanswerable (Lewandoski M. Nature Reviews Genetics, 2: 743-755, 2001).
Genetic analysis of transcription factors downstream of Fgf signaling.
In this project, we focus on the endpoint of FGF signaling by examining the role of homeobox transcription factors (GBX1, GBX2 and RX) that are downstream of FGF8 signaling. We focus on these particular factors because they are apparently involved in complex regulatory loops wherein they in turn may regulate Fgf8 expression.
In the absence of Rx numerous neural structures do not form including the stem cell population that will generate various structures of the eyes. Recently it has been shown that mutations in the human Rx gene causes congenital blindness due to anophthalmia and sclerocornea. By generating mice carrying a conditional Rx allele and inactivating this gene in the optic vesicle we have shown that Rx plays an essential role in the formation of both the lens and the neural retina. Rx promotes lens induction by activating genes expressing the secreted factors BMP4, and FGF8/15 in the presumptive neural retina. In the absence of Rx, retinal pigment epithelium forms in place of neural retina in the distal optic vesicle. These findings demonstrate that Rx controls the inductive interactions and cell fate decisions that are the hallmarks of early eye development.
In the absence of Gbx2 the mid/hindbrain doesn't form properly due to improper FGF8 signals from a structure called the isthmus. However, Gbx2 is expressed in a much larger set of embryonic regions where it apparently plays no role. Hypothesizing that a closely related gene, Gbx1 may compensate for Gbx2 in these regions we have reported the first detailed characterization of the mouse Gbx1 gene and show that it is expressed in a dynamic pattern during embryogenesis in many regions that overlap with Gbx2 (Waters S. et al., Gene Exp Patterns 3:313-17, 2003). We are currently characterizing mice lacking Gbx1 alone or lacking both Gbx1 and 2 to study the role of Gbx1 in regions where it is uniquely expressed (optic vesicles, hindbrain, genital region) and in regions where both genes may play redundant roles (gastrulation, neural tube, ventral forebrain).
Collaborators. Peter H. Mathers, Ph.D., West Virginia School of Medicine; John L.R. Rubenstein, M.D., Ph.D.., University of California, San Francisco.
Genetic analysis of signaling pathways during embryogenesis.
In this project we focus on the signal startpoint by studying genes encoding FGF ligands (Fgf4 or Fgf8) as well as genes in other signaling cascades thought to act with FGF signaling. This is because embryonic induction is often the result of a cell integrating more than one signal and there are many cases where FGFs are clearly only one part of the induction signal. In particular, we are examining the interaction between FGFs and bone morphogenic proteins (BMPs) by studying genes encoding the BMP receptors (Bmpr1a and (Bmpr1b). We are studying limb development and early mesoderm induction.
By inactivating Bmpr1a during limb development with different Cre lines we have shown that a BMP signal can have the opposite phenotype depending on context: the role of BMP signaling changes either with time or with limb identity. Early inactivation in the hindlimb results in the loss of Fgf8 expression and the cessation of hindlimb development. Latter inactivation in the forelimb results in a upregulation of Fgf4 and 8. We have shown through double and triple tissue specific inactivations of Bmpr1a and Fgf4/8 that BMPs control apoptosis during limb development by regulating FGF signaling.
We have generated a valuable Cre line, called TCre, that mediates recombination in the early gastrulating embryo. By inactivating Fgf8 with TCre we demonstrate that the only non-redundant role for Fgf8 in the mesodermal lineage is during kidney development, where Fgf8 is required for nephrogeneisis. We are now undertaking complex genetic experiments to inactivate Fgf8 pairwise with five other Fgfs expressed in the early embryo to undercover genetic redundancies. We hypothesize that a mix of different FGFs regulate early patterning events during development. It is our expectation that these experiments will make a major contribution to the role of FGF signaling.
Collaborators.: Alan O. Perantoni Ph.D. NCI-Frederick, Frederick MD; Seppo Vainio Ph.D. University of Oulu, Oulu Finland; Yuji Mishina, National Institute of Environmental Health Sciences, Research Triangle Park, NC; Olivier Ph.D. Pourquie Stowers Institute, Kansas City MO.
Limb Development 2010
The 11th International Conference of Limb Development and Regeneration will bring together investigators and students from around the world interested in all aspects of developing and regenerating limbs.
Topics that will be discussed include: pattern formation, integration of signaling pathways, limb regeneration, evolution, genomics and human malformation syndromes. This meeting will carry on the tradition of providing an informal setting with ample opportunities to meet colleagues, discuss work and form new collaborations.
For more information or to register, visit Limb 2010.
This page was last updated on 2/20/2013.