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Left cardiac isomerism in the Sonic hedgehog null mouse

Lookup NU author(s): Dr Victoria Hildreth, Stephen Webb, Dr Bill Chaudhry, Dr Jonathan Peat, Dr Helen PhillipsORCiD, Professor Bob Anderson, Professor Deborah HendersonORCiD


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Sonic hedgehog (Shh) is a secreted morphogen necessary for the production of sidedness in the developing embryo. In this study, we describe the morphology of the atrial chambers and atrioventricular junctions of the Shh null mouse heart. We demonstrate that the essential phenotypic feature is isomerism of the left atrial appendages, in combination with an atrioventricular septal defect and a common atrioventricular junction. These malformations are known to be frequent in humans with left isomerism. To confirm the presence of left isomerism, we show that Pitx2c, a recognized determinant of morphological leftness, is expressed in the Shh null mutants on both the right and left sides of the inflow region, and on both sides of the solitary arterial trunk exiting from the heart. It has been established that derivatives of the second heart field expressing Isl1 are asymmetrically distributed in the developing normal heart. We now show that this population is reduced in the hearts from the Shh null mutants, likely contributing to the defects. To distinguish the consequences of reduced contributions from the second heart field from those of left-right patterning disturbance, we disrupted the movement of second heart field cells into the heart by expressing dominant-negative Rho kinase in the population of cells expressing Isl1. This resulted in absence of the vestibular spine, and presence of atrioventricular septal defects closely resembling those seen in the hearts from the Shh null mutants. The primary atrial septum, however, was well formed, and there was no evidence of isomerism of the atrial appendages, suggesting that these features do not relate to disruption of the contributions made by the second heart field. We demonstrate, therefore, that the Shh null mouse is a model of isomerism of the left atrial appendages, and show that the recognized associated malformations found at the venous pole of the heart in the setting of left isomerism are likely to arise from the loss of the effects of Shh in the establishment of laterality, combined with a reduced contribution made by cells derived from the second heart field.

Publication metadata

Author(s): Hildreth V, Webb S, Chaudhry B, Peat JD, Phillips HM, Brown N, Anderson RH, Henderson DJ

Publication type: Article

Publication status: Published

Journal: Journal of Anatomy

Year: 2009

Volume: 214

Issue: 6

Pages: 894-904

ISSN (print): 0021-8782

ISSN (electronic): 1469-7580

Publisher: Wiley-Blackwell Publishing Ltd.


DOI: 10.1111/j.1469-7580.2009.01087.x


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Funder referenceFunder name
RG/02/004British Heart Foundation
RG/07/086British Heart Foundation