Situs Inversus in Dpcd/Poll(-/-), Nme7(-/-), and PkdIII(-/-) Mice

Situs inversus (SI) is a congenital condition characterized by left-right transposition of thoracic and visceral organs and associated vasculature. The usual asymmetrical positioning of organs is established early in development in a transient structure called the embryonic node. The 2-cilia hypothesis proposes that 2 kinds of primary cilia in the embryonic node determine left-right asymmetry: motile cilia that generate a leftward fluid flow, and immotile mechanosensory cilia that respond to the flow. Here, we describe 3 mouse S1 models that provide support for the 2-cilia hypothesis. In addition to having S1, Dpcd/Poll(-/-) mice (for: deleted in a mouse model of primary ciliary dyskinesia) and Nme7(-/-) mice (for: nonmetastatic cells 7) had lesions consistent with deficient ciliary motility: Hydrocephalus, sinusitis, and male infertility developed in Dpcd/Poll(-/-) mice, whereas hydrocephalus and excessive nasal exudates were seen in Nme7(-/-) mice. In contrast, the absence of respiratory tract lesions, hydrocephalus, and male infertility in PkdIII(-/-) mice (for: polycystic kidney disease I like I) suggested that dysfunction of motile cilia was not involved in the development of SI in this line. Moreover, the gene PkdIII has considerable sequence similarity with PkdI (for: polycystic kidney disease I), which encodes a protein (polycystin-I) that is essential for the mechanosensory function of immotile primary cilia in the kidney. The markedly reduced viability of PkdIII(-/-) mice is somewhat surprising given the absence of any detected abnormalities (other than SI) in surviving PkdIII(-/-) mice subjected to a comprehensive battery of phenotype-screening exams. However, the heart and great vessels of PkdIII(-/-) mice were not examined, and it is possible that the decreased viability of PkdIII(-/-) mice is due to undiagnosed cardiovascular defects associated with heterotaxy.