Figure 2

Huntingtin is required for formation of anterior primitive streak and paraxial mesoderm. Whole mount and section insitu hybridizations of E7.5 embryos shows T (Brachyury) (A-D) is expressed in the primitive streak, node, axial mesoderm and Evx1 (E-F) is expressed in the primitive streak, most strongly in the proximal streak wild-type embryos. However, in mutant embryos, both T (B, D) and Evx1 (F) are ectopically expressed in the extraembryonic region. Wnt3A expression is reduced in mutant embryos (H), although the localization of its expression to the proximal streak is the same as in wild-type embryos (G). Analysis of paraxial mesoderm markers Tbx6 (I,J) and Dll1 (K,L), reveals that these markers are reduced in mutant embryos (J,L), suggesting impaired paraxial mesoderm production in the absence of huntingtin. Embryos in A-H are shown in a lateral view with anterior oriented to the left. Embryos in I-L are shown in a posterior view (I,K) or near posterior (J,L) view with proximal oriented toward the top. In (C,D), al = allantois, a = amnion, ch = chorion, ee = embryonic node(N), em = extraembryonic mesoderm, n = node, ps = primitive streak. Rather than a node, mutant embryos exhibit a region of disorganized cells (*) at the distal extent of the short primitive streak.