PubMed · 6765831
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L Saxen. Neural induction.. https://pubmed.ncbi.nlm.nih.gov/6765831/
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A study of the sequences of the rhodopsin-encoding genes (Rh) in eight fish species from two of the major subdivisions of the teleosts reveals that no introns are present in the coding region. This contrasts with the opsin-encoding genes of all other vertebrates where either four or five introns are invariably found. Phylogenetic analysis shows that this intronless teleost Rh is homologous to the intron-containing Rh of amphibia, birds and mammals. Possible mechanisms for intron loss are discussed, including replacement by homologous conversion of Rh with a processed cDNA.
Ferritin is a highly conserved multisubunit protein in animals, plants and microbes which assembles with cubic symmetry and transports hydrated iron ions and protons to and from a mineralized core in the protein interior. We report here the high resolution structures of recombinant amphibian red-cell L ferritin and two mutants solved under two sets of conditions. In one mutant, Glu56, 57, 58 and 60 were replaced with Ala, producing a lag phase in the kinetics of iron uptake. In the second mutant, His25 was replaced with Tyr with, at most, subtle effects on function. A molecule of betaine, used in the purification, is bound in all structures at the 2-fold axis near the recently identified heme binding site of bacterioferritin and horse spleen L ferritin. Comparisons of the five amphibian structures identify two regions of the molecule in which conformational flexibility may be related to function. The positions and interactions of a set of 10 to 18 side-chains, most of which are on the inner surface of the protein, are sensitive both to solution conditions and to the Glu-->Ala mutation. A subset of these side-chains and a chain of ordered solvent molecules extends from the vicinity of Glu56 to 58 and Glu60 to the 3-fold channel in the wild type protein and may be involved in the transport of either iron or protons. The "spine of hydration" is disrupted in the Glu-->Ala mutant. In contrast, H25Y mutation shifts the positions of backbone atoms between the site of the mutation and the 4-fold axis and side-chain positions throughout the structure; the largest changes in the position of backbone atoms are in the DE loop and E helix, approximately 10 A from the mutation site. In combination, these results indicate that solvation, structural plasticity and cooperative structural changes may play a role in ferritin function. Analogies with the structure and function of ion channel proteins such as annexins are noted.
Limb regeneration is a phenomenon occurring only in some urodeles. The process seems to be initiated by the dedifferentiation of the terminally differentiated cells. These cells differentiate, subsequently, to the tissues that comprise the limb, thus reconstructing the pattern of the missing limb part. In this paper we review and present evidence that certain cell types of the limb have the capacity to differentiate to different cell types than their original one by cellular metaplasia. This switch is called transdifferentiation. The focus of this review is the process of dedifferentiation which is the necessary prerequisite for differentiation, and the possible mechanisms involved.