Volume 94, Issue 3, Pages 287-297 (August 1998) lefty-1 Is Required for Left-Right Determination as a Regulator of lefty-2 and nodal  Chikara Meno, Akihiko Shimono, Yukio Saijoh, Kenta Yashiro, Kyoko Mochida, Sachiko Ohishi, Sumihare Noji, Hisato Kondoh, Hiroshi Hamada  Cell  Volume 94, Issue 3, Pages 287-297 (August 1998) DOI: 10.1016/S0092-8674(00)81472-5

Figure 1 Targeting of lefty-1 Gene (A) The lefty-1 gene and targeting strategy. The relative positions of lefty-1 and lefty-2 on mouse chromosome 1 are shown at the top, with the direction of transcription indicated by arrows. The 7 kb upstream region of lefty-2 that was used to drive lacZ expression in Figure 7 is also indicated. K; KpnI. After homologous recombination, all the exons of lefty-1 (shaded boxes) are replaced by the neo gene. (B) Southern blot analysis of offspring obtained from the intercrossing of lefty-1+/− heterozygotes. Genomic DNA was digested with KpnI and subjected to hybridization with the probe indicated in (A). Arrows indicate the 10 kb (wild type) and 9 kb (mutant) fragments. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 2 Pulmonary Left Isomerism in lefty-1−/− Mice (A and B) Ventral view of the lungs of lefty-1+/− (A) and lefty-1−/− (B) mice. In the lefty-1+/− mice (A), the lungs are bilaterally asymmetric, with one left lobe and four right lobes (AL, accessory lobe; CaL, caudal lobe; CrL, cranial lobe; H, heart; ML, medial lobe; LL, left lobe; RL, right lobe). In the lefty-1−/− mice (B), both left and right lungs have one lobe. (C–F) Lateral view of the thorax from the left (C and D) and right (E and F), showing the relative positions of the pulmonary artery (pa) and the bronchus. Bronchi are indicated by blue lines. In the lefty-1+/− mice, the left bronchus is located caudal to the left pulmonary artery (C), whereas the right bronchus is positioned dorsal to the pulmonary artery (E). Furthermore, the branching pattern of the bronchi is asymmetric (C and E). In the lefty-1−/− mice, the branching pattern of the bronchi is symmetric and each bronchus is located caudal to the pulmonary artery on the left and right sides (D and F). la, left atrium; pa, pulmonary arteries; pv, pulmonary vein; ra, right atrium. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 3 L-R Positional Defects in lefty-1−/− Mice (A–L) lefty-1+/− (A–E) and lefty-1−/− (F–L) mice. L-R polarity is indicated. (A and F) Frontal view of the thorax. Note the abnormal positions of the aorta (ao) and pulmonary artery (pa), as well as the reduced lobation of the right lung in the homozygous mutant (F). ve, ventricule. (B, C, G, and H) Lateral views of the thorax from the right (B and G) and left (C and H). The azygos vein (az) is reversed to the right side in the mutant (G). CrL, cranial lobe of the lung; LL, left lobe of the lung; RL, right lobe of the lung; svc, superior vena cava. (D and I) The inferior vena cava (IVC, blue arrows) in the thorax. Note the presence of an IVC on each side in the mutant (I). AL, accesory lobe of the lung. (E and J) The IVC in the abdomen, showing the persistence of the azygos vein–IVC connection in the mutant (J). Arrowheads in (E) and (J) indicate the renal veins. ki, kidney. (K) Reversed viscera in the abdomen apparent in one of the mutants (group Z1, Table 1). Note that the stomach (st) and spleen (sp) are located on the right. (L) Reversed arching of the aorta (indicated by yellow arrow) detected in one of the mutants (group X, Table 1); other blood vessels, such as the pulmonary artery, showed abnormal connection and branching. (M) Inversion of the azygos vein and its connection to the IVC in the mutant mice. The aorta is shown in red, the vena cava in light blue, the azygos vein in dark blue, the kidney in pink, and the liver in yellow. The arrows indicate the direction of blood circulation. (N–S) The hearts of lefty-1−/− newborn mice were serially sectioned. (N and O) Sections from a group A mutant (Table 1) showing no obvious anomalies. (P and Q) Sections from a group C mutant showing TGA (transposition of the great arteries), ASD (atrial septal defect), and TAt (tricuspid atresia). (R and S) Sections from a group F mutant showing DORV. la, left atrium; lv, left ventricle; pa, pulmonary artery; ra, right atrium; rv, right ventricle. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 4 Bilateral Expression of lefty-2 and nodal in lefty-1 Mutant Embryos Expression of lefty-1 (A and B), lefty-2 (C–F, K and L), and nodal (G–J) in lefty-1+/− and lefty-1−/− embryos was examined by whole-mount in situ hybridization. Genotypes of the embryos are indicated at the top of each panel. (A–E and G–J) Anterior view; (F) distal view. Expression of lefty-2 is left-sided in lefty-1+/− embryos (C) but is bilateral in the lefty-1−/− embryos shown in (D–F). At the four-somite-pair stage (D), up-regulation of lefty-2 in the PFP is evident, but ectopic expression in right LPM is weak. At a slightly later stage (six somite pairs; [E]), the extent of lefty-2 expression in right LPM was increased and similar to that in left LPM. (F) Distal view of the lefty-1−/− embryo shown in (E). Expression of lefty-2 in left LPM extends to the posterior region, whereas the ectopic lefty-2 expression in right LPM does not. Expression of nodal is left-sided in lefty-1+/− embryos (G). However, it is either left-sided, bilateral, or right-sided in lefty-1−/− embryos (H–J), depending on developmental stage; (H) four somite pairs, (I and J) five somite pairs. (K and L) Transverse sections of the embryos shown in (C) and (D), respectively. Expression of lefty-2 in the PFP is weak and left-sided in the lefty-1+/− embryo (K), but it is up-regulated and bilateral in the lefty-1−/− embryo (L). Ectopic sites of lefty-2 expression are indicated by the arrows in (L). (M) the relation between the sites of lefty-2 and nodal expression and developmental stage. Both lefty-1+/− and lefty-1−/− embryos were recovered at E8.0 and their developmental stages determined by counting the number of somites. The expression sites of nodal and lefty-2, which were examined by whole-mount in situ hybridization, are summarized. Gray bars, no expression detected; blue bars, expression in left LPM; red bars, expression in right LPM; purple bars, bilateral expression in LPM. The nine embryos indicated by asterisks also showed up-regulated and bilateral expression of lefty-2 in the PFP. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 5 Bilateral Expression of Pitx2 in lefty-1−/− Embryos Expression of Pitx2 in lefty-1+/− (A and C–E) and lefty-1−/− (B, F, and G) embryos was examined by whole-mount in situ hybridization. (A and B) Anterior view of E8.0 embryos. Expression of Pitx2 in LPM (pink arrowheads), the sinus venosus, and vitelline vein (green arrowheads) is left-sided in the lefty-1+/− embryo (A) but bilateral in the lefty-1−/− embryo (B). (E) Lateral view of an E9.5 embryo. (C, D, and F–H) Transverse sections of E9.5 embryos; the approximate position of each section is indicated in (E). Expression of Pitx2 in the common cardinal vein (ccv), common atrial chamber (cac), and foregut (fg) is left-sided in the lefty-1+/− embryo (C and D) but is bilateral in the lefty-1−/− embryo (F and G). The regions corresponding to future lung bud are indicated by asterisks in (D) and (G). However, Pitx2 expression in the posterior region of the gut dorsal mesentery remained left-sided in the lefty-1−/− embryo (G and H, arrows). ld, liver diverticulum; st, septum transversum; uv, umbilical vein; va, vitelline artery. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 6 Bilateral Expression of a lefty-2–lacZ Transgene in lefty-1−/− Embryos lefty-1+/− mice containing a lefty-2–lacZ transgene (Figure 1A) were mated with lefty-1+/− mice. Expression of the transgene in lefty-1+/− (A–C) and lefty-1−/− (D–H) embryos was examined by X-Gal staining. (A, D, and G) Anterior views. (B and E) Posterior views. (C, F, and H) Transverse sections; the positions of the sections are indicated by the horizontal lines in (A), (D), and (G). Two types of X-gal staining patterns were observed in lefty-1−/− embryos. About two-thirds of lefty-1−/− embryos showed bilateral X-Gal staining in both the PFP and LPM (D–F). The arrows in (F) highlight the ectopic X-Gal staining in the right PFP and right LPM. The ectopic X-Gal staining in right LPM is confined to the anterior portion (E and F); the posterior region of right LPM, indicated by the asterisk in (F), is negative for X-Gal staining. In the remaining one-third of lefty-1−/− embryos (G and H), X-Gal staining in the PFP was up-regulated and bilateral, but X-Gal staining in LPM was left-sided. Anteroposterior (A–P) and left-right (L–R) axes are indicated. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)

Figure 7 A Model for the Role of lefty-1 and the Regulatory Relation among lefty-1, lefty-2, and nodal The hypothetical gene X encodes a long-range signaling molecule that regulates lefty-2 and nodal (X may be Shh, nodal, lefty-2, or an unknown gene). Solid arrows, activation; broken arrows, diffusion; solid bar, inhibition. See text for details. Cell 1998 94, 287-297DOI: (10.1016/S0092-8674(00)81472-5)