Transgenic mice carrying chimeric or mutated type III intermediate filament (IF) genes

Spatially Directed Proteomics of the Human Lens Outer Cortex Reveals an Intermediate Filament Switch Associated With the Remodeling Zone

PURPOSE

To quantify protein changes in the morphologically distinct remodeling zone (RZ) and adjacent regions of the human lens outer cortex using spatially directed quantitative proteomics.

METHODS

Lightly fixed human lens sections were deparaffinized and membranes labeled with fluorescent wheat germ agglutinin (WGA-TRITC). Morphology directed laser capture microdissection (LCM) was used to isolate tissue from four distinct regions of human lens outer cortex: differentiating zone (DF), RZ, transition zone (TZ), and inner cortex (IC). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the plasma membrane fraction from three lenses (21-, 22-, and 27-year) revealed changes in major cytoskeletal proteins including vimentin, filensin, and phakinin. Peptides from proteins of interest were quantified using multiple reaction monitoring (MRM) mass spectrometry and isotopically-labeled internal peptide standards.

RESULTS

Results revealed an intermediate filament switch from vimentin to beaded filament proteins filensin and phakinin that occurred at the RZ. Several other cytoskeletal proteins showed significant changes between regions, while most crystallins remained unchanged. Targeted proteomics provided accurate, absolute quantification of these proteins and confirmed vimentin, periplakin, and periaxin decrease from the DF to the IC, while filensin, phakinin, and brain acid soluble protein 1 (BASP1) increase significantly at the RZ.

CONCLUSIONS

Mass spectrometry-compatible fixation and morphology directed laser capture enabled proteomic analysis of narrow regions in the human lens outer cortex. Results reveal dramatic cytoskeletal protein changes associated with the RZ, suggesting that one role of these proteins is in membrane deformation and/or the establishment of ball and socket joints in the human RZ.

Expression of the HSF4 DNA binding domain-EGFP hybrid gene recreates early childhood lamellar cataract in transgenic mice

PURPOSE

The clinical management of cataracts in infancy involves surgical removal of the lens to ensure transmission of light to the retina, which is essential for normal neural development of the infant. This surgery, however, entails a lifelong follow-up and impaired vision. To our knowledge, no animal models recapitulate human lamellar opacities, the most prevalent form of early childhood cataracts. We present data on the recreation of the human lamellar cataract phenotype in transgenic mice.

METHODS

Mutations in the DNA binding domain (DBD) of the heat shock transcription factor 4 (HSF4) are known to be associated with early childhood autosomal dominant lamellar cataract. We used bacterial artificial chromosome (BAC) transgenesis to express a hybrid gene: Hsf4 (DBD)-enhanced green fluorescent protein (EGFP), by recombineering EGFP sequences into the DBD of the Hsf4 gene, to interfere with the DNA binding properties of Hsf4.

RESULTS

We recapitulated the human lamellar cataract, in its temporal as well as spatial presentation, within the transgenic mouse lens. This phenotype was reproduced faithfully using four different BACs, indicating that EGFP can be used to target transcription factor function in transgenic mice. Molecular and cell biological examination of early postnatal transgenic lens reveals impairment of secondary fiber cell differentiation.

CONCLUSIONS

Recreation of the human lamellar cataract phenotype in mice allows investigation of this human pathology at a level not possible previously and points to the relevance of fiber cell heterogeneity dictated by fiber cell-specific gene activity in the biogenesis of the lamellar cataract.

Molecular characteristics of inherited congenital cataracts

Congenital cataracts are a major cause of induced blindness in children, and inherited cataracts are the major cause of congenital cataracts. Inherited congenital cataracts have been associated with mutations in specific genes, including those of crystallins, gap junction proteins, membrane transport and channel proteins, the cytoskeleton, and growth and transcription factors. Locating and identifying the genes and mutations involved in cataractogenesis are essential to gaining an understanding of the molecular defects and pathophysiologic characteristics of inherited congenital cataracts. In this review, we summarize the current research in this field.

Lens intermediate filaments

The ocular lens assembles two separate intermediate filament systems sequentially with differentiation. Canonical 8-11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific beaded filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.

Synergism between phospholipase D2 and sorbitol accumulation in diabetic cataract formation through modulation of Na,K-ATPase activity and osmotic stress

Phospholipase D (PLD), a highly regulated enzyme that generates the second messenger phosphatidic acid, functions in signal transduction, membrane trafficking and cytoskeletal reorganization. PLD is thought to be involved in the pathogenesis of diabetic complications by activating PKC. Since PKC and PLD are present in the lens we sought to determine if PLD plays a role in diabetic cataract development. We developed transgenic mice that overexpress PLD2, one of the two mammalian isoforms of PLD. These mice developed congenital nuclear cataracts, but not diabetic cataracts. Histological analysis revealed vacuole formation in the fiber cells, mediated potentially by the substantially increased Na,K-ATPase activity. In the presence of the aldose reductase overexpressing transgene that increases lens osmotic pressure, these double transgenic mice developed more severe congenital cataract and became susceptible to develop diabetic cataract. Together, these data suggest that increased PLD2 activity in the lens under hyperglycemic condition might impair its osmoregulatory mechanism and reduce its ability to cope with the osmotic stress triggered by sorbitol accumulation.

General utility of the chicken betaB1-crystallin promoter to drive protein expression in lens fiber cells of transgenic mice

Transgenic mouse technology has been very valuable for the study of lens fiber cells since they can not be propagated in cell culture. The targeting of transgenes to the lens has traditionally been done with the alphaA-crystallin promoter. However, while lens-specific, transgenic lines made with the alphaA-crystallin promoter express the transgene at levels 100-300-fold lower than endogenous alphaA-crystallin. Here we propose an alternative, the chicken betaB1-crystallin promoter (-432/+30). Transgenic mice made with this promoter have successfully expressed CAT, d/n m-calpain, Weel, and betaB2-crystallin mRNA at levels comparable to the endogenous betaB1-crystallin gene and no eye abnormalities such as cataracts, have resulted. All of the transgenic lines made with the chicken betaB1-crystallin promoter have expressed the transgene in the lens fiber cells, and the best lines express at levels close to endogenous betaB1-crystallin. While RNA expression is very high, only moderate protein expression has been achieved, implying that the high protein expression of the crystallins is partially controlled at the level of translation. Thus, the chicken betaB1-crystallin promoter directs high level RNA expression to lens fiber cells, which may be especially useful for the expression of ribozyme and anti-sense RNAs in addition to ectopic proteins.

Mapping of the human CP49 gene and identification of an intragenic polymorphic marker to allow genetic linkage analysis in autosomal dominant congenital cataract

The CP49 protein is an intermediate filament protein expressed specifically in the lens fibre cells of the lens, where it is an important cytoplasmic structural component. Dominant-negative mutations in other intermediate filament proteins, such as keratins, cause disorders characterised by dense cytoplasmic aggregates in specific cell types. The CP49 gene is therefore a good candidate for dominantly inherited forms of cataract. To allow genetic linkage analysis of families with autosomal dominant cataract with respect to CP49, a highly polymorphic intragenic microsatellite marker for this gene has been developed. In addition, both low and high resolution radiation hybrid mapping of the CP49 gene has been completed, placing it very close to microsatellite marker D3S1290 on human chromosome 3q. Furthermore, using the intragenic CP49 microsatellite, linkage was excluded in four families with genetically uncharacterized forms of autosomal dominant congenital cataract.

The eye lens cytoskeleton

During lens cell differentiation there are a number of very characteristic morphological changes that occur. These include a 50- to 100-fold increase in cell length as the equatorial lens epithelial cells differentiate into fibre cells and the loss of the cellular organelles such as mitochondria, nuclei, Golgi apparatus and endoplasmic reticulum. Coincident with these changes are dramatic alterations in the organisation of the lens fibre cell cytoskeleton and in particular the lens-specific intermediate filament network comprising CP49 and filensin. Cell shape and cell polarisation as well as tissue integrity are all processes that depend upon the cytoskeleton and are therefore important to the lens. The unique aspects of the lenticular cytoskeleton are the subject of this review.

Reciprocal effect of optical isomerism of EW-dipeptides on immune response

Dipeptides of the EW-sequence, consisting of D-amino acids, were shown to inhibit spleen colony formation both after in vitro treatment of bone marrow and after the peptide injection to the donor 2-48 h prior to bone marrow taking. The inhibiting effect of D-(EW) peptides can be eliminated by injection of thymic cells to the recipient. L-(EW) peptides have no influence on colony forming activity of intact bone marrow cells but stimulate regeneration of colony formation by irradiated (1 Gy) bone marrow. Unlike L-(EW), the D-(EW) peptides suppress the development of hemopoietic stem cells into the S-phase. Supposedly, D-(EW) represent a new generation of immunoactive peptides possessing of inhibiting activity.

Zebrafish vimentin: molecular characterization, assembly properties and developmental expression

To provide a basis for the investigation of the intermediate filament (IF) protein vimentin in one of the most promising experimental vertebrate systems, the zebrafish (Danio rerio), we have isolated a cDNA clone of high sequence identity to and with the characteristic features of human vimentin. Using this clone we produced recombinant zebrafish vimentin and studied its assembly behaviour. Unlike other vimentins, zebrafish vimentin formed unusually thick filaments when assembled at temperatures below 21 degrees C. At 37 degrees C few filaments were observed, which often also terminated in aggregated masses, indicating that its assembly was severely disturbed at this temperature. Between 21 and 34 degrees C apparently normal IFs were generated. By viscometry, the temperature optimum of assembly was determined to be around 28 degrees C. At this temperature, zebrafish vimentin partially rescued, in mixing experiments, the temperature-dependent assembly defect of trout vimentin. Therefore it is apparently able to "instruct" the misorganized trout vimentin such that it can enter normal IFs. This feature, that assembly is best at the normal body temperature of various species, puts more weight on the assumption that vimentin is vital for some aspects of generating functional adult tissues. Remarkably, like in most other vertebrates, zebrafish vimentin appears to be an abundant factor in the lens and the retina as well as transiently, during development, in various parts of the central and peripheral nervous system. Therefore, promising cell biological investigations may now be performed with cells involved in the generation of the vertebrate eye and brain, and, in particular, the retina. Moreover, the power of genetics of the zebrafish system may be employed to investigate functional properties of vimentin in vivo.