Laminin alpha5 chain is required for intestinal smooth muscle development

Laminins (comprised of alpha, beta, and gamma chains) are heterotrimeric glycoproteins integral to all basement membranes. The function of the laminin alpha5 chain in the developing intestine was defined by analysing laminin alpha5(-/-) mutants and by grafting experiments. We show that laminin alpha5 plays a major role in smooth muscle organisation and differentiation, as excessive folding of intestinal loops and delay in the expression of specific markers are observed in laminin alpha5(-/-) mice. In the subepithelial basement membrane, loss of alpha5 expression was paralleled by ectopic or accelerated deposition of laminin alpha2 and alpha4 chains; this may explain why no obvious defects were observed in the villous form and enterocytic differentiation. This compensation process is attributable to mesenchyme-derived molecules as assessed by chick/mouse alpha5(-/-) grafted associations. Lack of the laminin alpha5 chain was accompanied by a decrease in epithelial alpha3beta1 integrin receptor expression adjacent to the epithelial basement membrane and of Lutheran blood group glycoprotein in the smooth muscle cells, indicating that these receptors are likely mediating interactions with laminin alpha5-containing molecules. Taken together, the data indicate that the laminin alpha5 chain is essential for normal development of the intestinal smooth muscle and point to possible mesenchyme-derived compensation to promote normal intestinal morphogenesis when laminin alpha5 is absent.     

Integrin alpha5beta1 supports the migration of Xenopus cranial neural crest on fibronectin

During early embryonic development, cranial neural crest cells emerge from the developing mid- and hindbrain. While numerous studies have focused on integrin involvement in trunk neural crest cell migration, comparatively little is known about mechanisms of cranial neural crest cell migration. We show that fibronectin, but not laminin, vitronectin, or type I collagen can support cranial neural crest cell migration and segmentation in vitro. These behaviors require both the RGD and "synergy" sites located within the central cell-binding domain of fibronectin. While these two sites are sufficient for cranial neural crest cell migration, we find that the second Heparin-binding domain of fibronectin can provide additional support for cranial neural crest cell migration in vitro. Finally, using a function blocking monoclonal antibody, we show that cranial neural crest cell migration on fibronectin requires the integrin alpha5beta1.     

Allometric and nonallometric components of Drosophila wing shape respond differently to developmental temperature

Phenotypic plasticity of wing size and shape of Drosophila simulans was analyzed across the entire range of viable developmental temperatures with Procrustes geometric morphometric method. In agreement with previous studies, size clearly decreases when temperature increases. Wing shape variation was decomposed into its allometric (24%) and nonallometric (76%) components, and both were shown to involve landmarks located throughout the entire wing blade. The allometric component basically revealed a progressive, monotonous variation along the temperature. Surprisingly, nonallometric shape changes were highly similar at both extremes of the thermal range, suggesting that stress, rather than temperature per se, is the key developmental factor affecting wing shape.     

The cytosolic chaperonin CCT associates to cytoplasmic microtubular structures during mammalian spermiogenesis and to heterochromatin in germline and somatic cells

Spermiogenesis, the haploid phase of spermatogenesis, is characterised by a dramatic cytodifferentiation of spermatids. The two major steps, nuclear shaping and cytoplasmic reorganisation of the organelles, rely on an extensive remodelling of the microtubule cytoskeleton. Folding of alpha- and beta-tubulin is mediated by the cytoplasmic chaperonin containing TCP-1 (CCT), highly expressed in testis. We studied CCT cellular distribution throughout spermatogenesis by immunofluorescence and immunoelectron microscopy. We unveil two main cytoplasmic localisations for CCT: at the centrosome and at the microtubules of the manchette, a structure unique to male germ cells. Both structures are essential for spermatid differentiation and may require CCT function. Although CCT is essentially cytoplasmic, a few reports suggest that a subset may have a nuclear localisation. We demonstrate that in the nucleus of germline and somatic cells, part of CCT associates to heterochromatin. In interphase cells, CCT seems generally confined to constitutive heterochromatin. Nevertheless, in condensing nucleus of future spermatozoon, it is also associated with chromatin undergoing compaction. Finally, in fully-condensed mitotic chromosomes, CCT is located all along the chromosomes. Our finding that CCT is associated with constitutive heterochromatin and to compacting chromatin raises the possibility that it may be implicated in maintenance and remodelling of heterochromatin.     

Intracellular maturation and transport of tumor necrosis factor alpha converting enzyme

The tumor necrosis factor alpha converting enzyme (TACE) activity is required for the shedding of a variety of biologically active membrane bound precursors. The activation of TACE necessitates the proteolytic cleavage of its prodomain, a process that was suggested to be catalyzed by the proprotein convertase furin. However, the involvement of furin in this activation process has never been experimentally demonstrated. We have shown that the furinlike cleavage site (R-V-K-R(214)) localized between the prodomain and the metalloprotease domain of TACE is the sole site that can be in vitro cleaved by furin. In Cos7 cells, the release of TACE-processed substrates was reduced by the overexpression of the furin-specific proprotein convertase inhibitor Portland alpha1-antitrypsin inhibitor, but the release of TACE-processed substrates was increased by overexpression of furin in LoVo cells (deficient in furin activity) in which a mature form of TACE was identified. The immature form of TACE was detected at the surface of LoVo cells and at the surface of Cos7 and HT29 cells upon proprotein convertase inhibition. These results suggest that furin is the major proprotein convertase involved in the maturation/activation of TACE which is not a prerequisite for its cell-surface expression.     

Telomeric transgenes and trans-silencing in Drosophila

Autonomous P elements, inserted in heterochromatic telomeric associated sequences (TAS) at the X chromosome telomere (site 1A) have strong P element regulatory properties that include repression of P-induced hybrid-dysgenesis and of P-lacZ expression in the germline. P-lacZ insertions or defective P elements at 1A in TAS can also repress in trans a euchromatic P-lacZ in the germline. This property has been called a trans-silencing effect (TSE). It requires some sequence-homology between the telomeric insertion and the euchromatic transgene. When repression is partial, variegating lacZ expression is observed, suggesting a chromatin-based component. TSE is observed only when the silencer transgenes are maternally inherited and occurs only in the female germline. We have evidence that this silencing also works in the presence of homologous non-P element sequences suggesting that homology-dependent silencing could be a general phenomenon in the female germline; such a system might have been subsequently adopted by the P element family, allowing its own repression.     

Microsatellite allele sizes: a simple test to assess their significance on genetic differentiation

The mutation process at microsatellite loci typically occurs at high rates and with stepwise changes in allele sizes, features that may introduce bias when using classical measures of population differentiation based on allele identity (e.g., F(ST), Nei's Ds genetic distance). Allele size-based measures of differentiation, assuming a stepwise mutation process [e.g., Slatkin's R(ST), Goldstein et al.'s (deltamu)(2)], may better reflect differentiation at microsatellite loci, but they suffer high sampling variance. The relative efficiency of allele size- vs. allele identity-based statistics depends on the relative contributions of mutations vs. drift to population differentiation. We present a simple test based on a randomization procedure of allele sizes to determine whether stepwise-like mutations contributed to genetic differentiation. This test can be applied to any microsatellite data set designed to assess population differentiation and can be interpreted as testing whether F(ST) = R(ST). Computer simulations show that the test efficiently identifies which of F(ST) or R(ST) estimates has the lowest mean square error. A significant test, implying that R(ST) performs better than F(ST), is obtained when the mutation rate, mu, for a stepwise mutation process is (a) >/= m in an island model (m being the migration rate among populations) or (b) >/= 1/t in the case of isolated populations (t being the number of generations since population divergence). The test also informs on the efficiency of other statistics used in phylogenetical reconstruction [e.g., Ds and (deltamu)(2)], a nonsignificant test meaning that allele identity-based statistics perform better than allele size-based ones. This test can also provide insights into the evolutionary history of populations, revealing, for example, phylogeographic patterns, as illustrated by applying it on three published data sets.