Evolutionary origins of the vertebrate heart: Specification of the cardiac lineage in Ciona intestinalis

Abstract

Here we exploit the extensive cell lineage information and streamlined genome of the ascidian, Ciona intestinalis, to investigate heart development in a basal chordate. Several cardiac genes were analyzed, including the sole Ciona ortholog of the Drosophila tinman gene, and tissue-specific enhancers were isolated for some of the genes. Conserved sequence motifs within these enhancers facilitated the isolation of a heart enhancer for the Ciona Hand-like gene. Altogether, these studies provide a regulatory framework for the differentiation of the cardiac mesoderm, beginning at the 110-cell stage, and extending through the fusion of cardiac progenitors during tail elongation. The cardiac lineage shares a common origin with the germ line, and zygotic transcription is first detected in the heart progenitors only after its separation from the germ line at the 64-cell stage. We propose that germ-line determinants influence the specification of the cardiac mesoderm, both by inhibiting inductive signals required for the development of noncardiac mesoderm lineages, and by providing a localized source of Wnt-5 and other signals required for heart development. We discuss the possibility that the germ line also influences the specification of the vertebrate heart.

Defining the transcriptional redundancy of early bodywall muscle development in C. elegans: evidence for a unified theory of animal muscle development

“…Although orthologs of several vertebrate muscletype-specific structural protein isoforms can be traced to ascidians, there is remarkably little conservation in expression patterns relative to muscle type (Meedel and Hastings 1993). For example, structural protein isoforms indicative of vertebrate cardiac muscle are present in ascidian bodywall muscle and vice versa (Chiba et al 2003), even though the ascidian heart is dependent on factors related to Nkx2.5 and HAND (Davidson and Levine 2003;Satou et al 2004). Coupled with our results, a model emerges in which a single ancestral contractile cell was dependent on a transcriptional hierarchy comprised of factors we now associate with several different muscle types.…”

ATP-binding Cassette Transporter A1 Contains a Novel C-terminal VFVNFA Motif That Is Required for Its Cholesterol Efflux and ApoA-I Binding Activities

“…Thus, the lack of the motif in transporters from the urochordate C. intestinalis and lower invertebrate organisms and its presence in transporters of fish, birds, and mammals indicate that the motif likely arose early in the divergence of the vertebrate lineage. This occurred ϳ450 million years ago, at a time when complex closed circulatory systems first evolved (37)(38)(39). Unlike the PDZ binding motif, the VFVNFA sequence is required for ABCA1 to form a complex with apoA-I and to transfer cholesterol to the apolipoprotein.…”

Early crest animals and the insight they provide into the evolutionary origin of craniates

“…The discovery of the Lower Cambrian tunicate Shankouclava , however, indicates that this animal group had already diverged morphologically from the main evolutionary course of the vertebrates by the Early Cambrian. Despite being departed from the main vertebrate evolutionary course for more than half a billion years and showing no crucial features in either its body plan (Lacalli, 2005) or genome (Holland, 2007) to link it directly to vertebrates in some aspects, tunicates yield many interesting clues that contribute to the dis- cussion of the evolutionary origin of the vertebrates with respect to neural crest cells (Jeffery et al, 2007), brain (Dufour et al, 2006), heart (Davidson and Levine, 2003;Simões-Costa et al, 2005), and eye lens (Shimeld and Purkiss, 2005).…”