Within the mammalian testis, specialized tight junctions between somatic Sertoli cells create basal and apical polarity within the cells, restrict movement of molecules between cells, and separate the seminiferous epithelium into basal and adluminal compartments. These tight junctions form the basis of the blood-testis barrier, a structure whose function and dynamic regulation is poorly understood. In this study, we used microarray gene expression profiling to identify genes with altered transcript levels in a mouse model for conditional androgen insensitivity. We show that testosterone, acting through its receptor expressed in Sertoli cells, regulates the expression of claudin 3, which encodes a transient component of newly formed tight junctions. Sertoli cell-specific ablation of androgen receptor results in increased permeability of the bloodtestis barrier to biotin, suggesting claudin 3 regulates the movement of small molecules across the Sertoli cell tight junctions. These results suggest that androgen action in Sertoli cells regulates germ cell differentiation, in part by controlling the microenvironment of the seminiferous epithelium. Our studies also indicate that hormonal strategies for male contraception may interfere with the blood-testis barrier.androgen receptor ͉ testosterone ͉ tight junctions

Androgen receptor function is required for male embryonic sexual differentiation, pubertal development and the regulation of spermatogenesis in mammals. During spermatogenesis, this requirement is thought to be mediated by Sertoli cells and its genetic and pharmacological disruption is manifested in spermatocytes as meiotic arrest. Through studies of a hypomorphic and conditional allele of the androgen receptor (Ar) gene, we have uncovered a dual post-meiotic requirement for androgen receptor activity during male germ cell differentiation. Observations in Ar hypomorphic animals demonstrate that terminal differentiation of spermatids and their release from the seminiferous epithelium is AR dependent and maximally sensitive to AR depletion within the testis. Cell-specific disruption of Ar in Sertoli cells of hypomorphic animals further shows that progression of late-round spermatids to elongating steps is sensitive to loss of Sertoli cell AR function, but that progression through meiosis and early-round spermatid differentiation are surprisingly unaffected.

Our group has shown that mechanical stimulation increases the stiffness of stem cell-collagen sponge constructs at 14 days in culture and subsequent rabbit patellar tendon repairs at 12 weeks postsurgery. What remains unclear is which genes might be responsible for this increase in stiffness. Therefore, the objective of this study was to determine how a tensile stimulus affects the gene expression of stem cell-collagen sponge constructs used to repair rabbit central patellar tendon defects. Tissue-engineered constructs were created by seeding mesenchymal stem cells (MSCs) from 10 adult rabbits at 0.14 x 10(6) cells/construct in type I collagen sponges. Half of the constructs were mechanically stimulated once every 5 min for 8 h/d to a peak strain of 2.4% for 2 weeks. The other half remained in an incubator without mechanical stimulation for 2 weeks. After 14 days in culture, half of the stimulated and nonstimulated constructs were prepared to determine the expression of collagen type I, collagen type III, decorin, fibronectin, and glyceraldehyde-3-phosphate dehydrogenase genes using real-time quantitative reverse transcriptase polymerase chain reaction. The remaining constructs were mechanically tested to determine their mechanical properties. Two weeks of in vitro mechanical stimulation significantly increased collagen type I and collagen type III gene expression of the stem cell-collagen sponge constructs. Stimulated constructs showed 3 and 4 times greater collagen type I (p = 0.0001) and collagen type III gene expression (p = 0.001) than nonstimulated controls. Stimulated constructs also had 2.5 times the linear stiffness and 4 times the linear modulus of nonstimulated constructs. However, mechanical stimulation did not significantly increase decorin or fibronectin gene expression (p = 0.2) after 14 days in culture. This study shows that mechanical stimulation of cell-sponge constructs produces similar increases in the expression of 2 structural genes, as well as linear stiffness and linear modulus.

SummaryProper functioning of the mammalian testis is dependent upon an array of hormonal messengers acting through endocrine, paracrine, and autocrine pathways. Within the testis, the primary messengers are the gonadotrophins, follicle stimulating hormone and luteinizing hormone, and the androgens. Abundant evidence indicates that the role of the gonadotrophins is to maintain proper functioning of testicular somatic cells. It is the androgens, primarily testosterone, which act through the somatic cells to regulate germ cell differentiation. Despite extensive research in this area, little is known about the cellspecific requirements for androgens and even less is understood about the downstream effectors of androgen signalling. However, recent work using cell-specific ablation of androgen receptor function has demonstrated a clear requirement for androgen signalling at multiple, discrete time points during spermatogenesis. These models also provide useful tools for identifying the targets of androgen receptor activity. The purpose of this review is to provide a brief overview of recent advances in our understanding of hormonal regulation of spermatogenesis, with an emphasis on the role of testosterone within the testis, and to pose important questions for future research in this field.

following correction should be noted. In Fig. 1b, the designed sequence of amino acids S 36 contains a typographical error in that only 35 of its 36 monomers appear. The missing amino acid is of type R and should be located between amino acids E (sixth) and G (seventh). The correct sequence is:Although this typographical error does not change the results presented in the paper because they were obtained with the correct number and sequence of amino acids, it constitutes a nuisance for anybody interested in reproducing our results, and we apologize for the inconvenience. We want to thank Prof. H. S. Chan, of the University of Toronto, for calling our attention to this error.Cell Biology. In the article "Quantitative analysis of biological membrane lipids at the low picomole level by nanoelectrospray ionization tandem mass spectrometry" by B. Brügger, G. Erben, R. Sandhoff, F. T. Wieland, and W. D.Lehmann, which appeared in number 6, March 18, 1997, of Proc. Natl. Acad. Sci. USA (94,(2339)(2340)(2341)(2342)(2343)(2344), Table 1