From Science to Writing: A Personal Perspective.

During my journey from scientist to writer, I confronted similar challenges. Scientists gather factual information to investigate Nature, but they also rely on narration and speculation to link discrete data points into a seamless story that fits current perspectives for acceptance; writers link specific events as steppingstones to write internally consistent stories that relate, however tenuously, to common experiences. The historical development of the gene concept exemplifies the narrative quality of science. Both science and writing, including fiction, always remain as works in progress. In addition to similarities, science and writing have complementary differences. Science involves performing experiments to resolve external mysteries of Nature; writing explores experiences to confront internal feelings. Scientists strive for meaningful conclusions, which are continually subject to change; writers, especially novelists, dwell in ambiguity and conflicts, which are never fully resolved. Taken together, I consider my efforts in science and writing as blended forms of creative self-expression.

Assembly of the cnidarian camera-type eye from vertebrate-like components.

Animal eyes are morphologically diverse. Their assembly, however, always relies on the same basic principle, i.e., photoreceptors located in the vicinity of dark shielding pigment. Cnidaria as the likely sister group to the Bilateria are the earliest branching phylum with a well developed visual system. Here, we show that camera-type eyes of the cubozoan jellyfish, Tripedalia cystophora, use genetic building blocks typical of vertebrate eyes, namely, a ciliary phototransduction cascade and melanogenic pathway. Our findings indicative of parallelism provide an insight into eye evolution. Combined, the available data favor the possibility that vertebrate and cubozoan eyes arose by independent recruitment of orthologous genes during evolution.

Conditional deletion of the mouse Klf4 gene results in corneal epithelial fragility, stromal edema, and loss of conjunctival goblet cells.

The Krüppel-like transcription factor KLF4 is among the most highly expressed transcription factors in the mouse cornea (B. Norman, J. Davis, and J. Piatigorsky, Investig. Ophthalmol. Vis. Sci. 45:429-440, 2004). Here, we deleted the Klf4 gene selectively in the surface ectoderm-derived structures of the eye (cornea, conjunctiva, eyelids, and lens) by mating Klf4-LoxP mice (J. P. Katz, N. Perreault, B. G. Goldstein, C. S. Lee, P. A. Labosky, V. W. Yang, and K. H. Kaestner, Development 129:2619-2628, 2002) with Le-Cre mice (R. Ashery-Padan, T. Marquardt, X. Zhou, and P. Gruss, Genes Dev. 14:2701-2711, 2000). Klf4 conditional null (Klf4CN) embryos developed normally, and the adult mice were viable and fertile. Unlike the wild type, the Klf4CN cornea consisted of three to four epithelial cell layers; swollen, vacuolated basal epithelial and endothelial cells; and edematous stroma. The conjunctiva lacked goblet cells, and the anterior cortical lens was vacuolated in Klf4CN mice. Excessive cell sloughing resulted in fewer epithelial cell layers in spite of increased cell proliferation at the Klf4CN ocular surface. Expression of the keratin-12 and aquaporin-5 genes was downregulated, consistent with the Klf4CN corneal epithelial fragility and stromal edema, respectively. These observations provide new insights into the role of KLF4 in postnatal maturation and maintenance of the ocular surface and suggest that the Klf4CN mouse is a useful model for investigating ocular surface pathologies such as dry eye, Meesmann's dystrophy, and Steven's-Johnson syndrome.

Reflections on basic science.

After almost 50 years in science, I believe that there is an acceptable, often advantageous chasm between open-ended basic research-free exploration without a practical destination and in which the original ideas may fade into new concepts-and translational research or clinical research. My basic research on crystalline (proteins conferring the optical properties of the eye lens) led me down paths I never would have considered if I were conducting translational research. My investigations ranged from jellyfish to mice and resulted in the gene-sharing concept, which showed that the same protein can have distinct molecular functions depending upon its expression pattern and, conversely, that different proteins can serve similar functional roles. This essay portrays basic science as a creative narrative, comparable to literary and artistic endeavors. Preserving the autonomy of open-ended basic research and recognizing its artistic, narrative qualities will accelerate the development of innovative concepts, create a rich resource of information feeding translational research, and have a positive impact by attracting creative individuals to science.

Targeted deletion of Dicer disrupts lens morphogenesis, corneal epithelium stratification, and whole eye development.

Dicer, a ribonuclease essential for miRNA processing, is expressed abundantly in developing mouse cornea and lens. We studied the roles of Dicer and miRNAs in eye development by conditionally deleting the Dicer gene in the mouse lens and corneal epithelium. Adult Dicer conditional null (DicerCN) mice had severe microphthalmia with no discernible lens and a poorly stratified corneal epithelium. Targeted deletion of Dicer effectively inhibited miRNA processing in the developing lens at 12.5 day of embryogenesis (E12.5). Lens development initiated normally but underwent progressive dystrophy between E14.5 and E18.5. Microarray analysis revealed activation of P53 signaling in DicerCN lenses at E13.5, consistent with increased apoptosis and reduced cell proliferation between E12.5 and E14.5. Expression of Pax6 and other lens developmental transcription factors were not greatly affected between E12.5 and E14.5 but decreased as the lens degenerated. Our data indicated an indispensible role for Dicer and miRNAs in lens and corneal development.

Differential expression patterns and developmental roles of duplicated scinderin-like genes in zebrafish.

Scinderin, the closest homologue of the actin-severing protein, gelsolin, has two similar paralogs (Scinla and Scinlb) in zebrafish. Scinla is abundant in the adult cornea; Scinlb comprises considerably less corneal protein. Here, we show that scinla is expressed in the nose, lens, brain, cornea and annular ligament of the iridocorneal angle; by contrast, scinlb is expressed in the hatching gland, floor plate, notochord, otic vesicle, brain, pharynx, cartilage, swim bladder and cornea. Activity of scinla and scinlb promoter fragments driving the EGFP reporter gene in transgenic zebrafish resembled scinla or scinlb expression. Previously, we showed that reduction of scinla by injection of antisense morpholino oligonucleotides ventralized embryos; here, specific reduction of scinlb expression led to subtle brain abnormalities associated with increased cell death, decreased shhb expression in the floor plate, and slightly reduced eye distance. Thus, scinla and scinlb have different expression patterns and developmental roles during zebrafish development.

Role of Pax genes in eye evolution: a cnidarian PaxB gene uniting Pax2 and Pax6 functions.

PaxB from Tripedalia cystophora, a cubomedusan jellyfish possessing complex eyes (ocelli), was characterized. PaxB, the only Pax gene found in this cnidarian, is expressed in the larva, retina, lens, and statocyst. PaxB contains a Pax2/5/8-type paired domain and octapeptide, but a Pax6 prd-type homeodomain. Pax2/5/8-like properties of PaxB include a DNA binding specificity of the paired domain, activation and inhibitory domains, and the ability to rescue spa(pol), a Drosophila Pax2 eye mutant. Like Pax6, PaxB activates jellyfish crystallin and Drosophila rhodopsin rh6 promoters and induces small ectopic eyes in Drosophila. Pax6 has been considered a "master" control gene for eye development. Our data suggest that the ancestor of jellyfish PaxB, a PaxB-like protein, was the primordial Pax protein in eye evolution and that Pax6-like genes evolved in triploblasts after separation from Cnidaria, raising the possibility that cnidarian and sophisticated triploblastic eyes arose independently.

Cubozoan crystallins: evidence for convergent evolution of pax regulatory sequences.

Cnidaria is the earliest-branching metazoan phylum containing a well-developed, lens-containing visual system located on specialized sensory structures called rhopalia. Each rhopalium in a cubozoan jellyfish Tripedalia cystophora has a large and a small complex, camera-type eye with a cellular lens containing distinct families of crystallins. Here, we have characterized J2-crystallin and its gene in T. cystophora. The J2-crystallin gene is composed of a single exon and encodes a 157-amino acid cytoplasmic protein with no apparent homology to known proteins from other species. The non-lens expression of J2-crystallin suggests nonoptical as well as crystallin functions consistent with the gene-sharing strategy that has been used during evolution of lens crystallins in other invertebrates and vertebrates. Although nonfunctional in transfected mammalian lens cells, the J2-crystallin promoter is activated by the jellyfish paired domain transcription factor PaxB in co-transfection tests via binding to three paired domain sites. PaxB paired domain-binding sites were also identified in the PaxB-regulated promoters of the J1A- and J1B-crystallin genes, which are not homologous to the J2-crystallin gene. Taken together with previous studies on the regulation of the diverse crystallin genes, the present report strongly supports the idea that crystallin recruitment of multifunctional proteins was driven by convergent changes involving Pax (as well as other transcription factors) in the promoters of nonhomologous genes within and between species as well as within gene families.

Gene expression of the mouse corneal crystallin Aldh3a1: activation by Pax6, Oct1, and p300.

PURPOSE: Aldehyde dehydrogenase 3a1 (Aldh3a1) represents approximately 50% of the water-soluble protein of the mouse corneal epithelial cells and thus, by analogy with the abundant lens crystallins, is considered a corneal crystallin. This study was conducted to examine the developmental pattern and transcriptional activation of Aldh3a1 gene expression in the mouse cornea. METHODS: Aldh3a1 mRNA and protein were analyzed by quantitative (Q)-PCR and Western immunoblot analysis. Functional promoter analysis was examined by cotransfecting plasmids containing variable portions of the Aldh3a1 promoter fused to the luciferase reporter gene into COS-7 cells with selected transcription factors. Transcription factor binding sites were identified by electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation assays (ChIP). In situ hybridization and immunohistochemistry were used to assess expression of Aldh3a1, Pax6, and Oct1 in the cornea. RESULTS: Aldh3a1 expression is temporally regulated in the cornea beginning at birth and increasing 100-fold by 6 weeks of age. Pax6, Oct1, and p300 synergistically activate the Aldh3a1 promoter approximately 116-fold. One Pax6 and two Oct1 binding sites were identified in vitro and in vivo in the Aldh3a1 promoter fragment analyzed. Pax6 and Oct1 are both present in the nuclei of corneal epithelial cells of the 6-week-old mouse. Finally, a reduction of Aldh3a1 correlated with reduced Pax6 in the corneas of heterozygous Small eye Pax6(+/-) mice. CONCLUSIONS: Pax6, Oct1, and p300 activate gene expression of the corneal crystallin Aldh3a1 in the mouse. These transcription factors are also implicated in the high expression of crystallin genes in the lens, consistent with the "refracton hypothesis" unifying many aspects of the lens and cornea.

Duplicated gelsolin family genes in zebrafish: a novel scinderin-like gene (scinla) encodes the major corneal crystallin.

We have previously identified a gelsolin-like protein (C/L-gelsolin) as a corneal crystallin in zebrafish. Here we show by phylogenetic analysis that there are at least six genes encoding gelsolin-like proteins based on their gelsolin domains in zebrafish: gsna and gsnb group with the vertebrate gelsolin gene, scina and scinb group with the scinderin (adseverin) gene, and scinla (C/L-gelsolin) and scinlb are novel scinderin-like genes. RT-PCR showed that scinla, scinlb, and gsnb are preferentially expressed in the adult cornea whereas gsna is expressed to a similar extent in cornea, lens, brain, and heart; scina and scinb expression were detectable only in whole zebrafish and not in these adult tissues. Quantitative RT-PCR and 2-dimensional polyacrylamide gel electrophoresis followed by MALDI/TOF mass spectroscopy confirmed high expression of beta-actin and scinla, moderate expression of scinlb, and very low expression of gsna and gsnb in the cornea. Finally, transgenic zebrafish carrying a green fluorescent protein reporter transgene driven by a 4 kb scinla promoter fragment showed expression in the cornea, snout, dorsal fin, and tail fin of 3-day-old zebrafish larvae. Our data suggest that scinla and scinlb are diverged paralogs of the vertebrate scinderin gene and show that scinla encodes the zebrafish corneal crystallin previously called C/L-gelsolin.

Regulation of the mouse alphaB-crystallin and MKBP/HspB2 promoter activities by shared and gene specific intergenic elements: the importance of context dependency.

The closely linked (863 bp), divergently arranged mouse myotonic dystrophy kinase binding protein (Mkbp)/HspB2 and small heat shock protein (shsp)/alphaB-crystallin genes have different patterns of tissue-specific expression. We showed previously that an intergenic enhancing region (-436/-257 relative to alphaB-crystallin transcription start site) selectively activates the alphaB-crystallin promoter in an orientation-dependent manner (Swamynathan, S.K. and J. Piatigorsky 2002. J. Biol. Chem. 277:49700-6). Here we show that cis-elements alphaBE1 (-420/-396) and alphaBE3 (-320/-300) functionally interact with glucocorticoid receptor (GR) and Sp1, respectively, both in vitro and in vivo. alphaBE1:GR regulates both the HspB2 and alphaB-crystallin promoters, while alphaBE3:Sp1 selectively regulates the alphaB-crystallin promoter, as judged by mutagenesis and co-transfection tests. Enhancer blocking assays indicate that the -836/-622 fragment can act as a negative regulator in transfection tests, raising the possibility that it contributes to the differential expression of the proximal HspB2 promoter and distal alphaB-crystallin promoter. Finally, experiments utilizing transiently transfected cells and transgenic mice show that two conserved E-box elements (-726/-721 and -702/-697) bind nuclear proteins and differentially regulate the HspB2 and alphaB-crystallin promoters in a tissue-specific manner. Taken together, our results indicate that the linked, differentially expressed HspB2 and alphaB-crystallin genes have evolved shared and promoter-preferred cis-control elements within the intergenic sequence. The context-dependency of cis-elements provides multiple opportunities for evolutionary novelty by small sequence changes.

Transketolase haploinsufficiency reduces adipose tissue and female fertility in mice.

Transketolase (TKT) is a ubiquitous enzyme used in multiple metabolic pathways. We show here by gene targeting that TKT-null mouse embryos are not viable and that disruption of one TKT allele can cause growth retardation ( approximately 35%) and preferential reduction of adipose tissue ( approximately 77%). Other TKT(+/-) tissues had moderate ( approximately 33%; liver, gonads) or relatively little ( approximately 7 to 18%; eye, kidney, heart, brain) reductions in mass. These mice expressed a normal level of growth hormone and reduced leptin levels. No phenotype was observed in the TKT(+/-) cornea, where TKT is especially abundant in wild-type mice. The small female TKT(+/-) mice mated infrequently and had few progeny (with a male/female ratio of 1.4:1) when pregnant. Thus, TKT in normal mice appears to be carefully balanced at a threshold level for well-being. Our data suggest that TKT deficiency may have clinical significance in humans and raise the possibility that obesity may be treated by partial inhibition of TKT in adipose tissue.

Structurally normal corneas in aldehyde dehydrogenase 3a1-deficient mice.

We have constructed an ALDH3a1 null mouse to investigate the role of this enzyme that comprises nearly one-half of the total water-soluble protein in the mouse corneal epithelium. ALDH3a1-deficient mice are viable and fertile, have a corneal epithelium with a water-soluble protein content approximately half that of wild-type mice, and contain no ALDH3a1 as determined by zymograms and immunoblots. Despite the loss of protein content and ALDH3a1 activity, the ALDH3a1(-/-) mouse corneas appear indistinguishable from wild-type corneas when examined by histological analysis and electron microscopy and are transparent as determined by light and slit lamp microscopy. There is no evidence for a compensating protein or enzyme. Even though the function of ALDH3a1 in the mouse cornea remains unknown, our data indicate that its enzymatic activity is unnecessary for corneal clarity and maintenance, at least under laboratory conditions.

Serial analysis of gene expression (SAGE) in the rat limbal and central corneal epithelium.

PURPOSE: To identify genes preferentially expressed in the stem-cell-rich limbal epithelium of the rat cornea. METHODS: The limbal and central corneal epithelial cells of 6-week-old rats were isolated by microdissection. Serial analysis of gene expression (SAGE) libraries were constructed and analyzed, and in situ hybridization, reverse transcription-polymerase chain reaction (RT-PCR) and cDNA cloning were conducted by conventional procedures. RESULTS: The rat limbal and central corneal epithelial SAGE libraries consisted of 41,894 and 40,691 tags, respectively. After annotation, this was reduced to 759 transcripts specific for the limbal library and 844 transcripts specific for the central corneal library; 2292 transcripts overlapped. Transcripts encoding proteins with metabolic functions comprised the major functional category in both libraries. In situ hybridization and/or RT-PCR results of 12 of the most abundant, highly enriched transcripts in the limbal epithelium were in general agreement with the SAGE data and showed that these proteins are also expressed in the conjunctival epithelium. Interesting limbal-enriched transcripts encode WDNM1-like protein (similar to WDNM1/Expi, a putative secreted proteinase and inhibitor of metastasis), mesothelin (a cancer marker), marapsin (a trypsin-like serine protease that may control cell growth and migration), K4 and K15 (both cytokeratins), and membrane-spanning four-domain subfamily A member 8B. WDNM1-like protein was cloned and confirmed as a member of the four-disulfide core family. CONCLUSIONS: The SAGE results extend the database of genes expressed in the rodent cornea and suggest an association between several genes preferentially expressed in the limbal epithelium with cellular proliferation and migration.

Role of aldehyde dehydrogenase isozymes in the defense of rat lens and human lens epithelial cells against oxidative stress.

PURPOSE: 4-Hydroxynonenal (HNE), a metastable lipid peroxidation product, is highly toxic to various cell types if not detoxified. Because of its constant exposure to light, the ocular lens continuously generates reactive oxygen species which, under conditions of oxidative stress, may lead to excessive lipid peroxidation and consequent formation of lipid-derived aldehydes (LDAs) such as HNE. The contribution of various isozymes of aldehyde dehydrogenase (ALDH) to the oxidation of LDAs has never been systematically investigated in the lens. The present study was undertaken to ascertain the role of ALDH1A1 and -3A1 in HNE metabolism and HNE-induced toxicity in cultured human lens epithelial cells (HLECs) and in rat and mouse lenses. METHODS: The metabolism of 3H-HNE was studied in ALDH3A1-knockout mouse lens and in HLECs transfected with ALDH1A1- or -3A1-specific antisense RNA and short interfering (Si)RNA. Appropriate controls were used, including wild-type mouse lens, scrambled oligonucleotides, and a transfection reagent. Transfected HLECs were exposed to oxidative stress (Fenton reaction) or HNE (30 microM) for 3 hours. Toxicity parameters, such as cell viability, apoptosis, and protein-HNE adducts and oxidation of exogenously added 3H-HNE were measured. Rat lenses were transfected with the SiRNA specific to ALDH1A1, and oxidation of 3H-HNE and the susceptibility of the transfected lenses to oxidation-induced opacification were measured. RESULTS: Rat lenses transfected with ALDH1A1-specific SiRNA, or cultured in the presence of the ALDH inhibitor cyanamide/disulfiram and subjected to oxidative stress displayed accelerated loss of transparency and a diminished capacity to oxidize HNE. Similarly, inhibition of ALDH1A1 in HLECs by ALDH1A1-specific antisense RNA or SiRNA was associated with decreased oxidation of 3H-HNE and increased susceptibility of the cells to oxidative damage, including apoptosis. Furthermore, 3H-HNE metabolism and HNE-induced toxicity were not affected in ALDH3A1-specific SiRNA- or antisense RNA-treated rat lenses, HLECs, or ALDH3A1-null mouse lenses. CONCLUSIONS: The results suggest that, under oxidative stress, HNE produced in the lens epithelium can cause toxicity and thus contribute to oxidation-induced cataractogenesis. Furthermore, the studies indicate that ALDH1A1 is a critical isozyme for maintaining clarity in human, rat, and mouse lenses.

Adaptive differences in the structure and macromolecular compositions of the air and water corneas of the "four-eyed" fish (Anableps anableps).

The water meniscus bisects the eyes of the "four-eyed" fish Anableps anableps, resulting in simultaneous vision in air and water. We compare the structure and macromolecular compositions of the Anableps dorsal (air) and ventral (water) corneas with the fully aquatic zebrafish cornea. The Anableps dorsal corneal epithelium is thicker (>20 cell layers), flatter (approximately 1.94 mm radius of curvature), and contains approximately 15-fold more glycogen (0.16 microg/microg water-soluble protein) than the ventral corneal epithelium (5-7 cell layers; approximately 1.63 mm radius of curvature; 0.01 microg glycogen/microg water-soluble protein), which resembles the zebrafish corneal epithelium. Gelsolin is the major water-soluble protein in the zebrafish (approximately 50%) and Anableps dorsal (approximately 38%) and ventral (approximately 21%) corneal epithelia, suggesting that gelsolin was recruited for high corneal expression before these two species diverged at least 100 million years ago and that abundant corneal gelsolin is not limited to aquatic vision. Anableps gelsolin, deduced from its cDNA, is 57% identical to zebrafish gelsolin. Paucity of Anableps corneal F-actin (consistent with high gelsolin) was confirmed by the absence of rhodamine-phalloidin staining. We suggest amphibious refraction and protection from UV irradiation and desiccation in air as selective constraints for the specializations of the Anableps dorsal cornea.

Cubozoan jellyfish: an Evo/Devo model for eyes and other sensory systems.

Cnidaria are the most basal phylum containing a well-developed visual system located on specialized sensory structures (rhopalia) with eyes and statocyts. We have been exploring the cubozoan jellyfish, Tripedalia cystophora. In addition to containing simple photoreceptive ocelli, each rhopalium in Tridedalia has a large and small complex, camera-type eye with a cellular lens containing three distinct families of crystallins which apparently serve non-lenticular functions. Thus, Tridpedalia recruited crystallins by a gene sharing strategy as have mollusks and vertebrates. Tripedalia has a single Pax gene, PaxB, which encodes a structural and functional Pax 2/5/8-like paired domain as well as an octapeptide and Pax6-like homeodomain. PaxB binds to and activates Tripedalia crystallin promoters (especially J3-crystallin) and the Drosophila rhodopsin rh6 gene in transfection tests and induces ectopic eyes in Drosophila. In situ hybridization showed that PaxB and crystallin genes are expressed in the lens, retina and statocysts. We suggest from these results that an ancestral PaxB gene was a primordial gene in eye evolution and that eyes and ears (mechanoreceptors) may have had a common evolutionary origin. Thus, the numerous structural and molecular features of Tridpalia rhopalia indicate that ancient cubozoan jellyfish are fascinating models for evo/devo insights into eyes and other sensory systems.

Postnatal gene expression in the normal mouse cornea by SAGE.

PURPOSE: To provide a detailed gene expression profile of the normal postnatal mouse cornea. METHODS: Serial analysis of gene expression (SAGE) was performed on postnatal day (PN)9 and adult mouse (6 week) total corneas. The expression of selected genes was analyzed by in situ hybridization. RESULTS: A total of 64,272 PN9 and 62,206 adult tags were sequenced. Mouse corneal transcriptomes are composed of at least 19,544 and 18,509 unique mRNAs, respectively. One third of the unique tags were expressed at both stages, whereas a third was identified exclusively in PN9 or adult corneas. Three hundred thirty-four PN9 and 339 adult tags were enriched more than fivefold over other published nonocular libraries. Abundant transcripts were associated with metabolic functions, redox activities, and barrier integrity. Three members of the Ly-6/uPAR family whose functions are unknown in the cornea constitute more than 1% of the total mRNA. Aquaporin 5, epithelial membrane protein and glutathione-S-transferase (GST) omega-1, and GST alpha-4 mRNAs were preferentially expressed in distinct corneal epithelial layers, providing new markers for stratification. More than 200 tags were differentially expressed, of which 25 mediate transcription. CONCLUSIONS: In addition to providing a detailed profile of expressed genes in the PN9 and mature mouse cornea, the present SAGE data demonstrate dynamic changes in gene expression after eye opening and provide new probes for exploring corneal epithelial cell stratification, development, and function and for exploring the intricate relationship between programmed and environmentally induced gene expression in the cornea.

Serum albumin in mammalian cornea: implications for clinical application.

PURPOSE: To compare the abundance and spatial distribution of serum albumin in the mouse and bovine cornea. METHODS: Serum albumin from cornea was separated from transketolase by SDS-PAGE (+/-dithiothreitol [DTT]) and identified by peptide sequencing and immunoblot analyses. The fractional content of serum albumin was determined in water-soluble extracts of cornea by imaging analyses after SDS-PAGE. Serum albumin was localized in cornea by immunohistochemistry and by SDS-PAGE analyses of samples from separated epithelium and stroma. RESULTS: SDS-PAGE (-DTT) resolved mouse serum albumin and transketolase and indicated that serum albumin was 13% of the water-soluble protein in whole mouse corneas. By contrast, corneal epithelial fractions contained little (<1%) serum albumin. Immunohistochemistry indicated that mouse serum albumin was present throughout the stroma between collagen lamellae. Immunohistochemical analyses of bovine cornea yielded similar results. In addition, immunohistochemistry for serum albumin revealed positive staining in a small number of basal epithelial cells next to Bowman's membrane, and greater staining in the anterior-peripheral stroma as well as immediately adjacent to Descemet's membrane. CONCLUSIONS: Mouse and bovine cornea have a similar content and spatial distribution of serum albumin. The appreciable serum albumin in the cornea documented here and elsewhere raise the possibility that it contributes to the physiological or optical functions of the cornea. Moreover, serum albumin's ability to bind drugs suggests that mice corneas could be exploited to study drug-serum albumin interactions in vivo and to test the usefulness of serum albumin as a drug carrier for corneal disorders.