Genetics of alcohol dehydrogenase and aldehyde dehydrogenase fromMonodelphis domesticacornea: further evidence for identity of corneal aldehyde dehydrogenase with a major soluble protein

Abstract

A didelphid marsupial, the gray short-tailed opossum (Monodelphis domestica), was used as a model species to study the biochemical genetics of alcohol dehydrogenases (ADHs) and aldehyde dehydrogenase (ALDH) in corneal tissue. Isoelectric point variants of corneal ALDH (designated ALDH3) and a major soluble protein in corneal extracts were observed among eight families of animals used in studying the genetics of these proteins. Both phenotypes exhibited identical patterns following PAGE-IEF and were inherited in a normal Mendelian fashion, with two alleles at a single locus (ALDH3) showing codominant expression. The data provided evidence for genetic identity of corneal ALDH with this major soluble protein, and supported biochemical evidence, recently reported for purified bovine corneal ALDH, that this enzyme constitutes a major portion of soluble corneal protein (Abedinia et al. 1990). Isoelectric point variants for corneal ADH were also observed, with patterns for the two major forms (ADH3 and ADH4) and one minor form (ADH5) being consistent with the presence of two ADH subunits (designated gamma and delta), and variant phenotypes existing for the gamma subunit. The genetics of this enzyme was studied in the eight families, and the results were consistent with codominant expression of two alleles at a single locus (designated ADH3). It is relevant that a major detoxification function has been proposed for corneal ADH and ALDH, in the oxidoreduction of peroxidic aldehydes induced by available oxygen and UV-B light (Holmes & VandeBerg, 1986a). In addition, a direct role for corneal ALDH as a UV-B photoreceptor in this anterior eye tissue has also been proposed (Abedinia et al. 1990).

Taxon-specific recruitment of enzymes as major soluble proteins in the corneal epithelium of three mammals, chicken, and squid.

“…As expected from previous studies (11)(12)(13)(14)(15)(16)(17)32), peptide sequencing indicated that the abundant 54-kDa proteins in the corneal epithelial cells of the three mammalian species that we examined are all identical to, or homologues of, (Fig. 4).…”

“…This does not exclude them also serving enzymatic (or other) functions in the cornea, although the abundance of some of the corneal epithelial enzymes appears to exceed what might be expected for strictly enzymatic needs. This has been already noted for the corneas of the rat (12,13), cow (15,16), opossum (14), and baboon (17), where class 3 ALDH makes up between 5% (baboon) and 40% (bovine) of the soluble protein. It has been suggested that the high concentration of baboon ALDH may function to protect the cornea by absorption of UV irradiation and by oxidizing aldehydes generated by light-induced peroxidation (17).…”

“…Although the stroma makes up the bulk of the cornea and is primarily responsible for its physical properties, it is possible that the thinner epithelial layer on the anterior surface of the cornea requires a sufficiently high concentration of structural proteins to minimize concentration fluctuations so that transparency will be assured (10). In this connection, we have been impressed by the fact that the tumor-inducible (class 3) aldehyde dehydrogenase (ALDH; EC 1.2.1.3) isoenzyme (11,12) is a major component of the cornea in the rat (13), opossum (14), cow (15,16), and baboon (17). Although the reasons for the striking accumulation of this enzyme in the cornea are not established, it appears reminiscent of the recruitment of enzymes in the lens to act as crystallins (see above).…”

Transketolase Is a Major Protein in the Mouse Cornea

“…The bovine and rabbit cornea epithelium exhibit high levels of PP activity (42,43,45), and PP activity can be stimulated in rabbit and chicken corneas upon exposure to oxidizing agents (42,60). Also consistent with this idea is the abundant expression of similarly protective enzymes in the cornea epithelium of various species (9,11,12,47,(61)(62)(63)(64)(65)(66).…”

Severely reduced recombination in females of the South American marsupial <i>Monodelphis domestic</i><i>a</i>

“…Monodelphis domestica is an especially well-suited spe cies on which to concentrate a major marsupial gene-mapping effort because of its significance as a model species for biomedi cal research (Ley et al, 1989;VandeBerg. 1990;Kusewitt et al, 1991) , its favorable husbandry and reproductive characteristics (VandeBerg, 1990), and its genetic diversity (van Oorschot et al, 1990, and unpublished data). Furthermore, genetic mapping using family studies would be expedited in this species because the chromosome number is low (2n = 18) and because chiasmata are fewer in females than in males and are located mainly in the telomeric regions .…”