Chapter 10 The Presence of Extralenticular Crystallins and its Relationship with Transdifferentiation to Lens

Clayton, R. M.; Jeanny, Jean-Claude; Bower, D. J.; Errington, L. H.

doi:10.1016/s0070-2153(08)60660-2

Cited by 37 publications

(19 citation statements)

References 36 publications

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“…Northern blot hybridization and western immunoblots indicate that the non-lens 6-crystallin RNA sequences comprise, at least in part, translatable mRNA (Agata et al, 1983;Bower et al, 1983;Ueda and Okada, 1986;Takagi, 1986;Linser and Irvin, 1987;Clayton et al, 1986;Cuthbertson et al, 1992). This is consistent with our finding that the 61-and 62-crystallin PCR products do not contain intron sequences, which are present in the genomic sequences between the primers we have used.…”

Section: Discussionsupporting

confidence: 90%

Differential expression of the two δ‐crystallin genes in lens and non‐lens tissues: Shift favoring δ2 expression from embryonic to adult chickens

Zelenka

Piatigorsky

1993

Developmental Dynamics

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Chicken argininosuccinate lyase (ASL)/G-crystallin, a lens enzyme-crystallin, is encoded in two linked genes (61 and 62); only the 62 polypeptide contains ASL activity. Here we have quantified 61-and $2-crystallin mRNA in the lens, cornea, neural retina, heart, and brain at different stages of embryonic development and in 1-wk-old and 1-yr-old chickens by the polymerase chain reaction using internal 61 and 62 RNA standards. The 61/S2 mRNA ratio differed for every tissue and was regulated during development. In the embryo there was more 61 than 62 mRNA in the lens (5CL100 times), cornea (5-4 times), and neural retina (2-20 times), about equal amounts of $1 and 62 mRNA in the heart, and more 62 mRNA in the brain (15 times). $1-Crystallin mRNA differentially decreased in every tissue after hatching; by contrast, the $2 mRNA remained about the same except for the lens, where it decreased 50-fold between 1 wk and 1 yr after hatching. In the 1-yr-old chicken, the 62/81 mRNA ratios were 7 in the lens, 175 in the cornea, 22 in the neural retina, 107 in the heart, and 136 in the brain, indicating that 62-crystallin is strongly favored in all adult tissues of the chicken. The excess of 61 to 62 mRNA in the embryonic lens, cornea, and neural retina is intriguing, and suggests some connection with developing transparent eye tissues. Finally, we raise the possibility that expression of both 8-crystallin genes may create tetrameric ASL isoenzymes (perhaps with different specific activities). The unexpected predominance of 62 mRNA in the 1-yr-old lens suggests that both the enzymatic and refractive functions of ASL/6-crystallin are operative and spatially separated, with the enzymatic role present in the cortical fibers and the refractive role in the center of the lens.

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Section: Discussionsupporting

confidence: 90%

Differential expression of the two δ‐crystallin genes in lens and non‐lens tissues: Shift favoring δ2 expression from embryonic to adult chickens

Zelenka

Piatigorsky

1993

Developmental Dynamics

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“…A sequence comparison ofthe two chicken S-crystallin genes and of human and yeast ASL is shown in Fig. 5 (44)(45)(46)(47)(48)(49), presumably expressed for enzymatic activity, will help resolve the nature of each 8-crystallin gene.…”

Section: Discussionmentioning

confidence: 99%

Gene sharing by delta-crystallin and argininosuccinate lyase.

Piatigorsky

O’Brien

Norman

et al. 1988

Proc. Natl. Acad. Sci. U.S.A.

254

191

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The lens structural protein -crystallin and the metabolic enzyme argininosuccinate lyase (ASL; Largininosuccinate argine-lyase, EC 4.3.2.1) have striking sequence similarity. We have demonstrated that duck & crystallin has enormously high ASL activity, while chicken 6crystallin has lower but significant activity. The lenses of these birds had much greater ASL activity than other tissues, suggesting that ASL is being expressed at unusually high levels as a structural component. In Southern blots ofhuman genomic DNA, chicken 61-crystallin cDNA hybridized only to the human ASL gene; moreover, the two chicken 8-crystallin genes accounted for all the sequences in the chicken genome able to cross-hybridize with a human ASL cDNA, with preferential hybridization to the 62 gene. Correlations of enzymatic activity and recent data on mRNA levels in the chicken lens suggest that ASL activity depends on expression of the 82-crystallin gene.The data indicate that the same gene, at least in ducks, encodes two different functions, an enzyme (ASL) and a structural protein (&crystallin), although in chickens specialization and separation of functions may have occurred.

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“…One could imagine that aA-crystallin fulfills some as yet unknown role as a minor but essential protein in cells outside the lens. Crystallins and their mRNAs have indeed been detected in trace amounts in nonlens tissues (37). In this connection, the relation of a-crystallin with the small heat shock proteins may also be recalled, although there is no indication that aEvolution: Hendriks et al…”

Section: Discussionmentioning

confidence: 99%

The lens protein alpha A-crystallin of the blind mole rat, Spalax ehrenbergi: evolutionary change and functional constraints.

Hendriks¹,

Leunissen²,

Nevo³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

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The complete structure of the single-copy aA-crystallin gene of the blind mole rat (Spalax ehrenbergi) has been determined in order to elucidate the evolutionary effects of the loss of vision on a lens-specific protein and its gene. The aA-crystallin gene appears to have all the necessary transcriptional and translational signal sequences to be expressed in the rudimentary lens of the mole rat and gives rise to probably two protein products by means of alternative splicing, as in rodents with normal vision. Comparisons of the blind mole rat aAcrystallin sequence with aA sequences from other rodents reveal a considerable acceleration of the substitution rate at nonsynonymous positions in the mole rat lineage, which reflects a relaxation of selective constraints, but the acceleration is not to the extent that might be expected if the gene were now without any function. The remaining evolutionary constraints still imposed upon the mole rat aA-crystallin gene may possibly reflect the need for a-crystallin expression as an indispensable component in the developmental program of the atrophied eye.Functional constraints working at the protein level are recognized as a major determinant of the rate of molecular evolution (1-3). Although several well-known examples clearly seem to illustrate this principle, such as the fastevolving fibrinopeptides versus the conserved histones (4), the structure-function relationships of most proteins are, in fact, not understood in sufficient detail to reliably correlate functional constraint with rate of evolution. This difficulty may also hamper the clear distinction of other types of constraints, such as amino acid composition (5), transcriptional and translational requirements (6), and developmental programs (7,8). The existence and importance of these additional selective forces might be revealed by studying genes whose protein products have lost their normal principal function in the course of evolution. The substitution rate of such a gene would be expected to increase and might eventually become as fast as in pseudogenes unless other constraints interfere. A unique opportunity for such a study is offered by the rudimentary eyes of blind vertebrate species. The eye-specific genes of these animals are no longer subject to the selective constraints associated with the maintenance of vision.The eye lens protein a-crystallin is very suitable for this purpose because much comparative and evolutionary data are available (9-11). a-Crystallin is a slowly evolving protein (10), and, thus, relaxation of constraints should be readily detectable. An important advantage, too, is the fact that the atA and aB subunits, of which at-crystallin is composed, are both encoded by single-copy genes located on different chromosomes (12). The aA and aB chains have =57% sequence homology, due to an ancient gene duplication (10), and conspicuous sequence similarity with the small heat shock proteins indicates that the ancestral ca-crystallin gene originated from this protein family (13,14). aA-Cry...

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Chapter 10 The Presence of Extralenticular Crystallins and its Relationship with Transdifferentiation to Lens

Cited by 37 publications

References 36 publications

Differential expression of the two δ‐crystallin genes in lens and non‐lens tissues: Shift favoring δ2 expression from embryonic to adult chickens

Differential expression of the two δ‐crystallin genes in lens and non‐lens tissues: Shift favoring δ2 expression from embryonic to adult chickens

Gene sharing by delta-crystallin and argininosuccinate lyase.

The lens protein alpha A-crystallin of the blind mole rat, Spalax ehrenbergi: evolutionary change and functional constraints.

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