crabp and maf highlight the novelty of the amphioxus club‐shaped gland

Abstract

 Abstract Jackman, W. R., Mougey, J. M., Panopoulou, G. D. and Kimmel, C. B. 2004. crabp and maf highlight the novelty of the amphioxus club-shaped gland. -Acta Zoologica (Stockholm) 85 : 91-99The club-shaped gland (csg) is a prominent organ during the development of amphioxus. However, the evolutionary significance of this pharyngeal structure has been a mystery because of the lack of an obvious corollary in vertebrates or other close relatives. To address the homology of the csg by molecular means, we report the cloning and expression patterns of two amphioxus genes expressed during its development, crabp and maf . Amphioxus maf is a bzip transcription factor expressed early in csg formation in the forming of the ventral duct of the gland. crabp encodes a cellular retinoic acid binding protein and is expressed widely in the csg later in its development. We compare these genes to the expression of AmphiKrox , a zinc-finger transcription factor previously reported to be expressed during csg development. Together these genes mark different spatial and temporal aspects of csg formation. However, we find little evidence to suggest homology of the csg with other organs in amphioxus or other chordates. We therefore propose that the csg can be viewed as an evolutionary novelty that probably arose within the amphioxus lineage.

Phylogenomic analysis and expression patterns of large Maf genes in Xenopus tropicalis provide new insights into the functional evolution of the gene family in osteichthyans

“…The only difference between these species is that, in the chick, the signal is restricted to the caudal half of each labeled somite, a regionalisation that is not observed in amphibians and teleosts. A large Maf expression in the somites was probably already present in the common ancestor of cephalochordates and vertebrates, since the unique Amphioxus large Maf gene shares this expression territory with its vertebrate MafA and MafB counterparts (Jackman et al 2004). Taken together, these data strongly suggest that this expression territory has been retained in amphibians and actinopterygians by the MafA and MafB, but not the c-Maf and Nrl classes, and subsequently lost by the MafB class in the lineage of amniotes (Fig.…”

From carrot to clinic: an overview of the retinoic acid signaling pathway

“…CRABP-like proteins of invertebrates, such as ascidian tunicates, amphioxus, annelids, nematodes or arthropods (Fig. 4), are members of the greater FABP family [56] without exhibiting a strong phylogenetic association with vertebrate CRABPs [17]. It is hence conceivable that RA binding of FABPs was acquired specifically in the lineage leading to extant vertebrates.…”

The club‐shaped gland of amphioxus: export of secretion to the pharynx in pre‐metamorphic larvae and apoptosis during metamorphosis

“…None of the morphology-based homologies listed in Table 1 has been widely accepted (the comparisons with the chordate mouth/ foregut or a chordate gill slit remain the best of an inconclusive lot). Finally, a recent review of developmental genetic data (Jackman et al 2004) gave no clear insights into homologies between the club-shaped gland and structures in other animals, and the authors suggested that the amphioxus club-shaped gland might be an evolutionary novelty that has arisen within the cephalochordate lineage.…”