Faculty Bibliography

Sequential expression of the K3/K12 keratin pair was studied during epithelial corneal differentiation, using monoclonal antibodies coupled with electrophoretic analysis. In the chick embryo, K12 appears on day 12, while K3 is present at least from day 11. By contrast, in the rabbit embryo, the expression of K12 (at 17 days) precedes that of K3 (at 21 days). In the adult rabbit, K3 is expressed without K12 in part of the limbus. Thus, within the corneal-type keratin pair, either the acidic or the basic partner appears first, according to the developmental stage or the species

The differentiation of mammalian urothelium culminates in the formation of asymmetrical unit membrane (AUM). Using gradient centrifugation and detergent wash, we purified milligram quantities of AUMs which, interestingly, contained three major proteins (15, 27, and 47 kDa) that appeared to be identical to the three immunoaffinity purified, putatively AUM-associated proteins that we described earlier (Yu, J., Manabe, M., Wu, X.-R., Xu, C., Surya, B., and Sun, T.-T. (1990) J. Cell Biol., 111, 1207-1216). Peptide mapping and immunoblotting established that these three proteins were distinct molecules. Using monospecific antibodies to these three proteins, we showed that they were all restricted to the superficial urothelial cells and were AUM-associated. The 27- and 15-kDa proteins were detected exclusively on the luminal side of mature, apical AUMs. In contrast, epitopes of the 47-kDa protein were detected on both sides of apical AUMs suggesting a transmembranous configuration. These results (i) provide the strongest evidence thus far that AUM contains three major proteins (the 27-kDa uroplakin I, 15-kDa uroplakin II, and 47-kDa uroplakin III) which form an extremely insoluble complex, (ii) suggest that uroplakin II, like uroplakin I (Yu, J., Manabe, M., Wu, X.-R., Xu, C., Surya, B., and Sun, T.-T. (1990) J. Cell. Biol. 111, 1207-1216), translocates from one side of the membrane to another during AUM maturation, (iii) indicate that uroplakin III may play a different structural role than uroplakins I and II in AUM formation, and (iv) establish the three uroplakins as markers for an advanced stage of urothelial differentiation

Although significant progress has recently been made in culturing mammalian urothelial cells, relatively little is known about their biochemical differentiation. In this paper, we assessed the differentiation state of cultured bovine urothelial cells by analyzing their keratins and a cell surface marker, uroplakin I. Urothelial cells were serially cultured either in a serum-free medium, or in a serum-containing medium in the presence of 3T3 feeder cells, with similar results. Despite their stratified appearance, both normal urothelium and cultured urothelial cells synthesize mainly K8, K18 and K19, keratins that are typically seen in simple epithelia. However, cultured urothelial cells synthesize a greatly increased amount of K5 and K6 keratins, which are usually expressed by stratified epithelia but present only in trace amounts in normal urothelium. These data indicate that, as far as keratin synthesis is concerned, cultured urothelial cells undergo an altered pattern of differentiation towards a more 'stratified phenotype'; this unusual finding has interesting implications for urothelial evolution. In the meantime, many superficial cells in cultured urothelial colonies make uroplakin I, a 27 x 10(3) Mr protein subunit of the asymmetrical unit membrane (AUM) characteristic of urothelial (superficial) umbrella cells. These results indicate that cultured urothelial cells undergo, at least in part, AUM biogenesis. Cultured urothelial cells thus provide a useful experimental model system for studying certain early steps of AUM formation

The luminal surface of mammalian urothelium is covered with numerous plaques (also known as the asymmetric unit membrane or AUM) composed of semi-crystalline, hexagonal arrays of 12-nm protein particles. Despite the presumed importance of these plaques in stabilizing the urothelial surface during bladder distention, relatively little is known about their protein composition. Using a mouse mAb, AE31, we have identified a 27-kD protein that is urothelium-specific and is differentially expressed in superficial umbrella cells. This protein (pI approximately 5.8) partitions into the detergent phase during Triton X-114 phase separation. Pulse-chase experiments using cultured bovine urothelial cells showed that this protein is synthesized as a 32-kD precursor that is processed through a 30-kD intermediate, to the mature 27-kD form. In cytoplasmic vesicles containing immature AUM, the AE31 epitope is detected in patches on the cytoplasmic side, but in mature, apical AUM it is detected exclusively on the luminal side. This suggests an unusual translocation of the AE31 epitope during AUM maturation; more data are required, however, to substantiate this interpretation. Immunoaffinity purification of the 27-kD protein results in the copurification in approximately molar ratio of a 15-kD protein, as well as a small and variable amount of a 47-kD protein. Immunoblotting data indicate that these three proteins are immunologically distinguishable. This copurified 15-kD protein is relative basic (pI approximately 8.0). Like the 27-kD protein, it is urothelium-specific and is present mainly in the umbrella cells. Together, our data indicate that a 27-kD protein is urothelial plaque-associated (uroplakin I). Based on complex formation data, we provisionally name the 15-kD protein uroplakin II; additional data will be required to determine whether this and the 47-kD protein are integral parts of AUM. The identification of these AUM-associated and -related proteins, plus the availability of a culture system capable of synthesizing and processing some of these molecules, offer new opportunities for studying the detailed structure, assembly, and function of asymmetrical unit membrane

Inconsistent with the view that hair follicle stem cells reside in the matrix area of the hair bulb, we found that label-retaining cells exist exclusively in the bulge area of the mouse hair follicle. The bulge consists of a subpopulation of outer root sheath cells located in the midportion of the follicle at the arrector pili muscle attachment site. Keratinocytes in the bulge area are relatively undifferentiated ultrastructurally. They are normally slow cycling, but can be stimulated to proliferate transiently by TPA. Located in a well-protected and nourished environment, these cells mark the lower end of the 'permanent' portion of the follicle. Our findings, plus a reevaluation of the literature, suggest that follicular stem cells reside in the bulge region, instead of the lower bulb. This new view provides insights into hair cycle control and the possible involvement of hair follicle stem cells in skin carcinogenesis

Destruction of corneal surface was created in one eye of 24 rabbits by n-heptanol corneal epithelial debridement and surgical removal of limbal zone. One month later, the animals were equally subdivided into three groups of eight for limbal transplantation, conjunctival transplantation, and control without transplantation. During a 6-month postoperative follow-up, all corneas in the control group showed progressive vascularization and conjunctivalization. All corneas with limbal transplantation showed progressive decrease of vascularity, verified by fluorescein angiography. In contrast, all but one of the eight corneas of conjunctival transplantation showed progressive vascularization (P = 0.01). More important, the resultant epithelia showed corneal phenotype in limbal transplantation, but remained conjunctival in conjunctival transplantation, as verified by monoclonal antibodies AM-3, APSM-1, and AE-5. These results support the concept of the limbal location of corneal epithelial stem cells, and indicate that complete destruction of the limbal zone resulted in corneal vascularization and conjunctivalization, and that limbal transplantation has a better efficiency than conjunctival transplantation in restoring such destroyed corneal surface