Activation of Rac1 or Cdc42 during early morphogenesis of eye discs induces ectopic antennae in Drosophila

Promotion of immune and glycaemic functions in streptozotocin-induced diabetic rats treated with un-denatured camel milk whey proteins

T cell mediated autoimmune diabetes is characterized by immune cell infiltration of pancreatic islets and destruction of insulin-producing β-cells. This study was designed to assess the effect of whey proteins (WP) on the responsiveness of lymphocytes in rats after four months of Streptozotocin (STZ)-induced Type 1 diabetes (T1D). A diabetic group was supplemented with WP daily for five weeks at a dose of 100 mg/kg. Ribonucleic acid (RNA) was extracted from stimulated lymphocytes in order to analyse gene expressions using real time PCR and RT-PCR. PCR results were confirmed with ELISA. The proliferation capacity of lymphocytes and their homing to the spleen were studied. Antigen-activated lymphocytes showed that diabetes impaired the mRNA expression of the protein kinase B (Akt1), Cdc42, and the co-stimulatory molecule, CD28, which are important for cell survival, actin polymerization and T cell activation, respectively. Accordingly, proliferation of lymphocytes was found to be suppressed in diabetic rats, both in vivo and in vitro. WP was found to restore Akt1, Cdc42 and CD28 mRNA expression during diabetes to normal levels. WP, therefore, served to activate the proliferation of B lymphocytes in diabetic rats both in vivo and in vitro. Although WP was found to up-regulate mRNA expression of both interleukin (IL)-2 and interferon gamma (IFN-γ), it suppressed the proliferation activity of almost all T cell subsets. This was confirmed by WP normalizing the structure and function of ß cells. Meanwhile, WP was found to down regulate the mRNA expression of Tumor necrosis factor-alpha (TNF-α) and its programmed cell death-receptor (Fas). Taken together, the results of this study provide evidence for the potential impact of WP in the treatment of immune impairment in T1D, suggesting that it serves to reverse autoimmunity by suppressing autoreactive T cells and down regulating TNF-α and Fas, resulting in improved pancreatic ß cell structure and function.

Signaling role of Cdc42 in regulating mammalian physiology

Cdc42 is a member of the Rho GTPase family of intracellular molecular switches regulating multiple signaling pathways involved in actomyosin organization and cell proliferation. Knowledge of its signaling function in mammalian cells came mostly from studies using the dominant-negative or constitutively active mutant overexpression approach in the past 2 decades. Such an approach imposes a number of experimental limitations related to specificity, dosage, and/or clonal variability. Recent studies by conditional gene targeting of cdc42 in mice have revealed its tissue- and cell type-specific role and provide definitive information of the physiological signaling functions of Cdc42 in vivo.

Rac1 modulation of the apical domain is negatively regulated by β (Heavy)-spectrin

Epithelial polarity and morphogenesis require the careful coordination of signaling and cytoskeletal elements. In this paper, we describe multiple genetic interactions between the apical cytoskeletal protein β(H) and Rac1 signaling in Drosophila: activation of Rac1 signaling by expression of the exchange factor Trio, is strongly enhanced by reducing β(H) levels, and such reductions in β(H) levels alone are shown to cause an increase in GTP-Rac1 levels. In contrast, co-expression of a C-terminal fragment of β(H) (βH33) suppresses the Trio expression phenotype. In addition, sustained expression of βH33 alone in the eye induces a strong dominant phenotype that is similar to the expression of dominant negative Rac1(N17), and this phenotype is also suppressed by the co-expression of Trio or by knockdown of RacGAP50C. We further demonstrate that a loss-of-function allele in pak, a Rac1 effector and negative regulator of β(H)' dominantly suppresses larval lethality arising loss-of-function karst (β(H)) alleles. Furthermore, expression of constitutively active Pak(myr) in the larval salivary gland induces expansion of the apical membrane and destabilization of the apical polarity determinants Crumbs and aPKC. These effects resemble a Rac1 activation phenotype and are suppressed by βH33. Together, our data suggest that apical proteins including β(H) are negatively regulated by Rac1 activation, but that Rac1 signaling is also suppressed by β(H) through its C-terminal domain. Such a system would be bistable with either Rac1 or β(H) predominant. We suggest a model for apical domain maintenance wherein Rac1 down-regulation of β(H) (via Pak) is opposed by β(H)-mediated down-regulation of Rac1 signaling.

Light-induced translocation of Drosophila visual Arrestin2 depends on Rac2

Photoreceptor cells are remarkable in their ability to adjust their sensitivity to light over a wide range of intensities. Rapid termination of the photoresponse is achieved in part by shuttling proteins in and out of the light-transducing compartment of the photoreceptor cells. One protein that undergoes light-dependent translocation is the rhodopsin regulatory protein arrestin. However, the mechanisms coupling rhodopsin to arrestin movement are poorly understood. Here we show that light-dependent shuttling of the major arrestin in Drosophila photoreceptor cells, Arrestin2 (Arr2), occurs independently of known elements of the phototransduction cascade. Disruptions of the trimeric G protein, phospholipase Cbeta, the TRP channel, or the Na(+)/Ca(2+) exchanger did not influence Arr2 localization. Rather, we found that loss of the small GTPase Rac2 severely impaired Arr2 movement and prolonged the termination of the photoresponse. Our findings demonstrate that light-induced translocation of Arr2 occurs through a noncanonical rhodopsin/Rac2 pathway, which is distinct from the classical phototransduction cascade.

Transformation of eye to antenna by misexpression of a single gene

In Drosophila, the eye and antenna originate from a single epithelium termed the eye-antennal imaginal disc. Illumination of the mechanisms that subdivide this epithelium into eye and antenna would enhance our understanding of the mechanisms that restrict stem cell fate. We show here that Dip3, a transcription factor required for eye development, alters fate determination when misexpressed in the early eye-antennal disc, and have taken advantage of this observation to gain new insight into the mechanisms controlling the eye-antennal switch. Dip3 misexpression yields extra antennae by two distinct mechanisms: the splitting of the antennal field into multiple antennal domains (antennal duplication), and the transformation of the eye disc to an antennal fate. Antennal duplication requires Dip3-induced under proliferation of the eye disc and concurrent over proliferation of the antennal disc. While previous studies have shown that overgrowth of the antennal disc can lead to antennal duplication, our results show that overgrowth is not sufficient for antennal duplication, which may require additional signals perhaps from the eye disc. Eye-to-antennal transformation appears to result from the combination of antennal selector gene activation, eye determination gene repression, and cell cycle perturbation in the eye disc. Both antennal duplication and eye-to-antennal transformation are suppressed by the expression of genes that drive the cell cycle providing support for tight coupling of cell fate determination and cell cycle control. The finding that this transformation occurs only in the eye disc, and not in other imaginal discs, suggests a close developmental and therefore evolutionary relationship between eyes and antennae.