Theembryonicmidgutmustrotateinacomplexyetstereotypicalpatterntoassumethefamiliarpositioning within the body cavity. Failure of this process causes malrotation and predisposes to catastrophic midgut volvulus, a strangulation of the gut and associated vasculature. Our research has established the highly conserved molecular mechanisms by which the mechanical rotation of the gut is achieved, orchestrated by the conserved symmetry breaking transcription factor Pitx2. More recently we have shown that the same organasymmetrymechanismspatternthecomplexnetworkofbloodandlymphaticvesselsthatsupplyand drain the vertebrate gut. Thus with one core molecular repertoire, the developing gut assumes early structural, molecular and vascular asymmetries that determine the form and function of the adult organ. In the dorsal mesentery, a bridge of mesodermal tissue that suspends the gut within the body cavity, the arteries and lymphatics that supply the future gut arise downstream of a Pitx2-??Cxcl12 signaling pathway, which directs the progressive assembly of Cxcr4-??positive angioblasts into endothelial cords and patent vessels.WehaveshownthatlossofPitx2,Cxcr4orCxcl12functiondisruptsarteryandlymphaticformation specifically in the gut, and targets a novel population of lymphatic precursors that is distinct from those derived from mesenteric lymph sac. Gut lymphatics have a crucial role in absorption of dietary lipids, a functionthatseparatesthemfromallotherlymphaticnetworksinthebody.Whileourdatahighlightthatthe eventual formation of lymphatics depends on the prior assembly of the arterial network, the specific mechanismsofthisrelationshipremainunclear.
Inour firstaim, weaddressthespecificrolesandtimingof Pitx2 expression during lymphatic patterning and physiology. Using Pitx2 mutant mouse lines, we will connect the earliest embryonic laterality pathways with organ-??intrinsic patterns of lymphatic vasculature in thegut.
Inour secondaim, wetesttherelationshipbetweenPitx2andVegf-??Cinthemousegutandutilizing the accessibility of chicken embryo. In our third aim, we will ablate Cxcr4 in arterial, lymphatic or generalizedendotheliumusingCx40-??,Prox1-??andTie2-??CREdriversoftamoxifen-??inducibleCre.Wewilltest the ability of Cxcr7, a second receptor for Cxcl12, to compensate for Cxcr4 loss using Cxcr7 mutant and reporter mice. Lessons learned from these experiments will change the way we consider and study lymphatics of the mammalian intestine, and will shed new light on potential targets of local lymphatics in diseasesofthegut.
Intestinal lymphatics are the essential channels for absorption and transport of dietary lipids and figure prominently in the pathogenesis of multiple debilitating intestinal metabolic diseases. We have discovered a novel specific population of precursor cells that give rise to gut lymphatics and developed genetic tools to addresshowthisnetworkformsatthemolecularandcellularlevel.Usingthechickeneggandgeneticmouse models, we will reveal specific interactions that separate lymphatics in the gut from elsewhere in the body, highlightingsignalingpathwaysthatmightbetargetedwithnoveltherapies.
