Biomedical subjects

Ann S N Lau

Publications and source records attributed to Ann S N Lau.

3 recordsLinked to original sources

PubMed2005

Crosstalk between Rab GTPases and cell junctions.

For the past several years, studies from other laboratories, as well as ours, have begun to unravel the mechanism of germ cell movement in the testis by using several in vitro and in vivo models of tight and adherens junction assembly and disassembly, two cellular phenomena that confer cell movement. However, for cell movement to be fully appreciated, the importance of "intracellular" cell movements, such as those involving actin and microtubule filaments, must be better understood. Recent research on Rab GTPases has shown that members of this superfamily function in the trafficking of vesicles containing cargo to distinct subcellular sites such as the plasma membrane while utilizing actin and microtubule filaments as tracks. In this mini-review, we provide an overview of Rab GTPase structure, function, and regulation, while placing added emphasis on the role of Rabs in cell junction dynamics in the testis.

Animals↗

PubMed2003

Rab8B GTPase and junction dynamics in the testis.

Throughout spermatogenesis, germ cells migrate from the basal to the adluminal compartment while remaining attached to Sertoli cells via actin-based adherens and intermediate filament-based anchoring junctions. However, the events that trigger deadhesion and adhesion remain largely unknown. As part of our continued effort in elucidating the mechanism of germ cell movement, we have examined the role of Rab8B, a GTPase probably participating in intracellular trafficking events at the site of the adherens junction. By RT-PCR Rab8B mRNA was found in the brain, testis, heart, kidney, and spleen. Immunohistochemical studies revealed that Rab8B was concentrated predominantly in the basal compartment, localizing to a similar site at which immunoreactive E-cadherin was found. Additional experiments demonstrated that Rab8B associated with the actin, intermediate filament, and microtubule cytoskeletal networks. When Sertoli cells were cultured at high density or germ cells were cocultured with Sertoli cells, Rab8B increased significantly during junction assembly. Moreover, inclusion of germ cell-conditioned medium in Sertoli cell cultures resulted in stimulation of Rab8B expression. Conversely, treatment of adult rats with 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide reduced Rab8B mRNA and protein levels, coinciding with the time of germ cell loss from the epithelium. Taken collectively, these studies suggest that Rab8B participates in adherens junction dynamics in the testis.

Adherens Junctions↗

PubMedDate not supplied

Role of tissue inhibitor of metalloproteases-1 in junction dynamics in the testis.

Using multiple high-performance liquid chromatography steps, we have identified and purified a polypeptide to apparent homogeneity from primary Sertoli cell conditioned culture medium that consisted of 2 molecular variants of 31 and 29 kDa when electrophoresed on a sodium dodecyl sulfate-polyacrylamide gel run under reducing conditions. Partial N-terminal amino acid sequence analysis of these 2 proteins revealed a sequence of NH(2)-IKMAKMLKGFDAVGNATG, which is homologous to tissue inhibitor of metalloproteases-1 (TIMP-1). Studies by semiquantitative reverse transcription-polymerase chain reaction using a primer pair specific to rat TIMP-1 demonstrated that both Sertoli and germ cells express TIMP-1. During maturation, the steady-state TIMP-1 mRNA level in the testis increased significantly from 40 to 60 days of age, which suggests its role in the restructuring of the epithelium during spermiation. This increase in testicular TIMP-1 expression was apparently not due to the increase in germ cell number, because TIMP-1 expression decreased approximately fivefold in germ cells isolated from testes of aging rats. Using Sertoli cells cultured at low (0.05 x 10(6) cells/cm(2)) and high (0.5 x 10(6) cells/cm(2)) densities, it was found that TIMP-1 expression increased transiently but significantly during junction assembly. A similar induction of TIMP-1 mRNA was also detected in Sertoli-germ cell cocultures during germ cell adhesion onto Sertoli cells. More important, the inclusion of either alpha(2)-macroglobulin (a protease inhibitor produced by Sertoli cells) or aprotinin (a serine protease inhibitor) into an in vitro germ cell adhesion assay facilitated the attachment of fluorescently labeled germ cells onto the Sertoli cell epithelium when compared to control, which suggests that the assembly of adherens junctions may involve protease inhibitors.

Adherens Junctions↗