The Michael M. Shen Lab - Research Interests

Role of Cripto in anterior-posterior patterning:
In our initial studies, we examined the effects of a null mutation for Cripto in mice, and found that Cripto is required for the correct orientation of the anterior-posterior (A-P) axis in the early embryo. In detailed in situ hybridization studies, we observed that the expression of Cripto during pre-gastrulation and gastrulation stages is highly dynamic, and is associated with early signs of overt A-P asymmetry. Homozygous Cripto^-/-embryos generated by targeted gene disruption die shortly after gastrulation at embryonic day 8.5, and display severe defects in formation of the primitive streak and embryonic mesoderm. These homozygous mutants are mostly comprised of anterior neuroectoderm, and lack posterior structures, thus resembling a head without a trunk. To determine the basis for these defects, we analyzed the expression of markers for the A-P axis. Notably, we found that markers of the prospective anterior side are located in the distal visceral endoderm, while early markers of the posterior primitive streak are localized in the proximal epiblast. Our results indicated that Cripto signaling is essential for the conversion of a proximal-distal asymmetry into an orthogonal A-P axis.

Expression of Cripto and phenotype of null mutants. Nature 395: 702-707 (1998)

Requirement for Cryptic in left-right axis specification:
We have also found that the EGF-CFC gene Cryptic is required for formation of the L-R axis. In particular, we showed that the expression of Cryptic is L-R symmetric in the lateral plate mesoderm, node, notochordal plate, and prospective floor plate, and precedes the asymmetric expression of several regulatory factors in the L-R pathway, including Nodal, Lefty2, and Pitx2 in the lateral plate mesoderm, and of Lefty1 in the prospective floor plate. We have found that null mutation for Cryptic results in L-R laterality defects, including randomized abdominal situs, pulmonary right isomerism, severe cardiac defects, and vascular heterotaxia, as well as randomized embryo turning and cardiac looping. In Cryptic mutant embryos, L-R asymmetric expression does not occur in the lateral plate mesoderm, while Lefty1 expression is absent from the prospective floor plate. Notably, L-R asymmetric expression of Nodal at the lateral edges of the node is still observed in Cryptic mutants, suggesting that L-R specification has occurred in the node but not the lateral plate mesoderm. We proposed that a signaling pathway mediated by EGF-CFC activities is essential for transfer of L-R positional information from the node. In addition, these results support the idea that EGF-CFC proteins act as essential co-factors for the TGFβ related factor Nodal.

Asymmetric expression of Nodal around the node in Cryptic mutants. Genes Dev. 13: 2527-2537 (1999)