MMPs are required for embryonic heart development and lumen formation.

<p>(A) In stage 16 wildtype embryos labelled with MEF-2 antibody, CBs form bilateral rows and migrate collectively towards the dorsal midline (arrow). (A’) At stage 17, contralateral CBs align at the midline and form a lumen (arrow). (B-B’) In <i>mmp1</i>^<i>Q112</i><i>/ mmp1</i>^<i>Q112</i> null mutants (from here on referred to as <i>mmp1</i>), organization of CB rows is uneven and delayed migration of CBs is observed (asterisk), however they reach the midline and form a reduced size lumen (arrow). (C-D’) In <i>mmp2</i>^<i>w307</i><i>/ mmp2</i>^<i>w307</i> and <i>mmp1</i>^<i>q112</i>, <i>mmp2</i>^<i>w307</i><i>/ mmp1</i>^<i>q112</i>, <i>mmp2</i>^<i>w307</i> null mutants (from here on referred to as <i>mmp2</i> and <i>mmp1</i>,<i>mmp2</i>, respectively), organization of CBs along the bilateral rows is disrupted and CB migration is delayed (asterisk). The CBs in the heart region do not reach the midline by stage 17 (arrow). (E-H) Cross sectional views of stage 17 hearts labelled with α-Mef-2, α-Dg and α-Dlg are visualised (E-H). (E) In wildtype, Dg localises to the CB luminal domain (arrowhead) and pericardial cells (asterisk) while Dlg localises to the junctional domains (arrow). (F) In <i>mmp1</i> mutants, a reduced Dg labeled lumen forms (arrowhead) and Dlg labels the enlarged junctional domain (arrow). (G) In <i>mmp2</i> and <i>mmp1</i>,<i>mmp2</i> mutants, CBs fail to adhere to contralateral partners (arrowhead). CBs exhibit rounded morphology and Dg localises along an extended apical domain (arrowhead). (E’-H’) Representation of CBs at stage 17 in wildtype and <i>mmp1</i>, <i>mmp2</i> and <i>mmp1</i>,<i>mmp2</i> mutants summarising distribution of Dg (green), Dlg (red) and Mef2 (blue). Posterior is to the right in dorsal view images (A-D). Scales—25 μm in A-D’ and 10 μm in E-H’.