Date of Degree

2-2016

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Dr. Nathalia Holtzman

Advisor

Dr. Nathalia Holtzman

Committee Members

Dr. Nathalia Holtzman

Dr. Colin Phoon

Dr. Cathy Savage-Dunn

Dr. Kimara Targoff

Dr. Daniel Weinstein

Subject Categories

Biology | Cell and Developmental Biology | Molecular Biology

Keywords

Heart development, wt1, cardiac contractions, cardiac development, cell migration

Abstract

The outer cardiac layer, the epicardium, coordinates the final steps of vertebrate heart development. This cardiac tissue arises from cells in the proepicardial organ (PEO) that forms around the base of the inflow tract. Its general location is conserved across species despite morphological differences. Cellular mechanisms of migration differ across species. Three strategies of PEO migration are described: 1) The floating cyst model - PEO cells released into the pericardial cavity are directed by fluid movements to migrate onto the myocardium; 2) Villi transfer - cardiac contractions may mediate multicellular PEO villi contact to the myocardium; and 3) Tissue bridge-mediated transfer - PEO cells migrate along a bridge to contact the myocardium. All currently described mechanisms suggest the same strategies for coverage of both cardiac chambers. Using zebrafish, we demonstrate distinct mechanisms of atrial and ventricular PEO migration. We introduce a novel concept of chamber-specific epicardium formation. This concept opens new avenues to investigate chamber-specific epicardium regulation and epicardial-derived cell fate.

In addition, we discovered PEO villi in close proximity to the ventricular myocardium surface. To demonstrate the cardiac contractility requirement for villi-mediated PEO migration, cardiac contractions were inhibited using two chemicals and one genetic mechanism and assayed for migrated cells. Cardiac contractions are required for ventricular epicardium formation. Surprisingly, we found atrial epicardium in embryos with inhibited cardiac contractions.

Our results indicate chamber-specific PEO cell migration mechanisms: Atrium-specific migration is independent of cardiac contractions as cells migrate directly on the atrial myocardium surface. Ventricle-specific migration is dependent on cardiac contractions. Our identification of chamber-specific PEO subpopulations and chamber-specific migration mechanisms establish a new chamber-specific perspective to investigate regulation of epicardium formation and regulation of epicardial-derived cells.

Supplemental Movie 1.mov (22310 kB)
Villous moving with beat of the ventricular myocardium surface

Supplemental Movie 2.mov (39872 kB)
tcf21-positive proepicardial cysts in the pericardial cavity

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