Mark B. Lewandoski, Ph.D.
Dr. Lewandoski has made seminal contributions to the development of the Cre/loxP system for the conditional control of gene expression in mice. He has applied these approaches and other aspects of mouse genetics to an analysis of embryonic development, in particular, limb development, somitogenesis, and axis extension. In this work he focuses on Fibroblast Growth Factor (FGF) signaling, which controls most aspects of cellular behavior, including apoptosis, differentiation, gene regulation and programmed cell death. He also investigates how the embryo integrates FGF signals with other pathways, notably that of WNT and BMP signaling.
We strive to understand how cellular signaling controls embryonic development. With this effort, we contribute to a body of knowledge that is necessary to understand how aberrant or deregulated molecular signals cause disease, including cancer. Our entry into work is a focus in Fibroblast Growth Factors (FGFs), a major signaling family that governs arguably some aspect of every cellular behavior during normal development and is increasingly important in cancer therapies as our knowledge of its role in oncogenesis expands. In particular, the FGFs we study play important roles in human breast cancer and prostate cancer. Also, it is clear that complex crosstalk between different pathways regulates both normal and abnormal biology. Therefore, our analysis of genetic crosstalk between FGFs, WNTs and BMPs in development, may potentially reveal insights into similar interactions during cancer.
With this effort, we have generated a number of novel genetic models of failed embryonic development. In doing so, we have provided a number of useful tissue-specific Cre mouse lines to the community, thereby expanding this technology.
Limb Development. We have contributed to a large body of work that describes an essential role for Fibroblast Growth Factor (FGF) signaling during limb development by examining mice lacking genes that encode FGF ligands and receptors. Another important signaling pathway during limb development is controlled by Bone Morphogenetic Proteins (BMPs), which control many aspects of limb outgrowth -- early patterning in all three axes, programmed cell death and bone formation. Therefore we have set ourselves the task to understand how BMP and FGF signaling pathways interact during limb development.
As part of this work, we are studying the role of BMP signaling as effectors of normal programmed cell death that occurs in mesenchymal interdigit cells, thus removing them and sculpting the final digit pattern so that animals are born without webbed digits. In previous work we produced genetic evidence for a novel model in which the surface ectoderm must receive a BMP signal, resulting in down regulation of Fgfs which in turn induces apoptosis of the underlying mesenchyme. Thus we demonstrated that BMPs control programmed cell death indirectly, by regulating FGF signaling. However, it is important to emphasize that this insight does not exclude a direct role for BMP signaling in controlling cell death in the developing limb. Therefore we extended these studies by studying the role of BMP and FGF signaling in various aspects of limb development using mouse lines that express Cre in specific regions of the developing limb.
Thus, we are asking are BMPs direct effectors of normal programmed cell death? If so, how do BMPs achieve this endpont? In a serendipitous discovery, we have found that removal of a BMP signal to the limb bud interdigit zone rescues the requirement for a BMP signal to the digit region of the developing limb. Our efforts to understand this rescue may lead to a fundamental understanding of patterning in the developing limb. In other studies, we have uncovered an important node of signaling between FGFs and BMP that is essential for normal development of the limb skeleton. This linking of the two signaling pathways is not only a unique insight into how the limb is patterned but may provide a model for how the two pathways interact in other developmental contexts or during cancer.
Embryonic growth and somitogenesis. We use complex mouse genetics to understand the role of FGF signaling in mesodermal lineages with a special emphasis on extension of the body axis and formation of somites (segmented mesodermal segments that are the building blocks of vertebrate muscle, dermis and vertebral bodies). Our work has made clear that genetic redundancy is an important aspect of this biology; therefore all work in this project emerges from an effort to comprehensively characterize the genetic redundancy of FGF signaling in the mesodermal lineage. Such work is relevant to many cases of cancer where more than one FGF gene may be damaged. To achieve this, we have generated and characterized important Cre mouse lines, which are tools that allow the control of gene expression in the early embryo. These include TCre (expressed in the early emerging nascent mesoderm), TCreERT2 (activatable in emerging nascent mesoderm at all embryonic stages) and Tbx4-Cre (expressed in a posterior mesodermal domain that includes the allantois, hindlimb, and external genitalia). TCre in particular has had a major impact on the field, being essential in well over 20 publications. Besides providing the mouse genetics community with valuable mouse lines, this project has yielded insights that document our major insights regarding FGF signaling in the early embryo. In collaboration with Alan Perantoni (NCI), we demonstrated that Fgf8 was essential for development of the kidney and male reproductive tract. We showed that Fgf8, together with Fgf4, are required for essential aspects of somitogenesis, which include expression of oscillating gene domains, WNT pathway genes and markers of undifferentiated presomitic mesoderm.
Importantly, we demonstrated that a lack of FGF signaling results in the premature differentiation of the entire presomitic mesoderm. This functional redundancy that we uncovered has implications for cancer as both FGFs have been found to be aberrantly active in testicular tumors. Furthermore this redundancy has implications for evolution as the same FGFs play compensatory roles in limb development. We are continuing to study genetic redundancy in FGF signaling in several aspects of embryonic development. For example, we are investigating the role of Fgf3 in termination of the embryonic axis. We are investigating the role of Fgf4 and Fgf8 in the differentiation of the somite into its derivative lineages (muscle and bone). In another part of this project, we are studying the role of these Fgfs in development of the allantois, a tissue that gives rise to the placental blood vessels and the umbilical cord. In human, failure of this tissue to develop properly underlies many aspects of pregnancy loss. Finally, to address the deficiency in the community's knowledge of what defines an FGF target gene, we have initiated work to molecularly define the cis-acting elements that cause FGF targets genes to respond to FGF signals.
Selected Key Publications
- Dev Biol. Mar 15;411(2): 266-76, 2016. [ Journal Article ]
- Genesis. Feb;54(2): 91-8, 2016. [ Journal Article ]
TCreERT2, a transgenic mouse line for temporal control of Cre-mediated recombination in lineages emerging from the primitive streak or tail bud.PLoS ONE. 8: e62479, 2013. [ Journal Article ]
- Proc Natl Acad Sci U S A. 108: 4018-23, 2011. [ Journal Article ]
- Nat Rev Genet. 2: 743-55, 2001. [ Journal Article ]
Dr. Lewandoski received his Ph.D. in Microbiology from The New York University Medical Center in 1988. After completing postdoctoral research as an American Cancer Society Fellow under Dr. Gail R. Martin at the University of California, San Francisco (UCSF), he continued his work as a Research Anatomist in the Anatomy Department at UCSF. In 1999, Dr. Lewandoski established the Genetics of Vertebrate Development Section.
|Matthew J. Anderson, Ph.D.||Staff Scientist|
|Michael Boylan Ph.D.||Postdoctoral Fellow (CRTA)|
|Cynthia M. Elder||Biological Laboratory Technician|
|Salvia Misaghian||Postbaccalaureate Fellow (CRTA)|