Biomedical subjects

M D Franco

Publications and source records attributed to M D Franco.

5 recordsLinked to original sources

PubMed2001

Differential and overlapping expression patterns of X-dll3 and Pax-6 genes suggest distinct roles in olfactory system development of the African clawed frog Xenopus laevis.

In Xenopus laevis, the formation of the adult olfactory epithelium involves embryonic, larval and metamorphic phases. The olfactory epithelium in the principal cavity (PC) develops during embryogenesis from the olfactory placode and is thought to respond to water-borne odorants throughout larval life. During metamorphosis, the PC undergoes major transformations and is exposed to air-borne odorants. Also during metamorphosis, the middle cavity (MC) develops de novo. The olfactory epithelium in the MC has the same characteristics as that in the larval PC and is thought to respond to water-borne odorants. Using in situ hybridization, we analyzed the expression pattern of the homeobox genes X-dll3 and Pax-6 within the developing olfactory system. Early in development, X-dll3 is expressed in both the neuronal and non-neuronal ectoderm of the sense plate and in all cell layers of the olfactory placode and larval PC. Expression becomes restricted to the neurons and basal cells of the PC by mid-metamorphosis. During metamorphosis, X-dll3 is also expressed throughout the developing MC epithelium and becomes restricted to neurons and basal cells at metamorphic climax. This expression pattern suggests that X-dll3 is first involved in the patterning and genesis of all cells forming the olfactory tissue and is then involved in neurogenesis or neuronal maturation in putative water- and air-sensing epithelia. In contrast, Pax-6 expression is restricted to the olfactory placode, larval PC and metamorphic MC, suggesting that Pax-6 is specifically involved in the formation of water-sensing epithelium. The expression patterns suggest that X-dll3 and Pax-6 are both involved in establishing the olfactory placode during embryonic development, but subtle differences in cellular and temporal expression patterns suggest that these genes have distinct functions.

Animals↗

PubMed1994

Regions of the CD8 molecule involved in the regulation of CD2-mediated activation.

The CD8 molecule regulates T cell activation mediated via the CD3 T cell receptor and the adhesion molecule CD2. CD8 mAbs have been found to inhibit early (Ca2+ rise) as well as late events (cytotoxicity, proliferation, and lymphokine secretion) mediated via the CD2 pathway. A panel of eight anti-human CD8 mAbs was tested for inhibition of CD2-mediated Ca2+ rise in a cytotoxic T cell clone. The inhibition ranged from 5 to 53% independently of mAb isotype and affinity measured by half saturation binding. We then characterized these mAbs for their reactivity toward three mutants of the human CD8 alpha carrying amino acid sequence changes in the surface-exposed loops homologous to the immunoglobulin CDR1, 2, and 3. The mutations included replacement of the human CD8 alpha CDR1- and CDR2-like loops by the homologous mouse sequences and the insertion of a glycine in the middle of the CDR3-like loop. Thus, five mAbs were found to be affected by the mutation in the CDR2-like loop but not by alterations in the other CDR-like loops. Conversely, the other two mAbs (8E1.7 and B9.8) were affected only by mutations in the CDR1- and CDR3-like loops, respectively. Cross-inhibition experiments were essentially in agreement with these results. Interestingly, all the mAbs directed against the CDR2-like loop were potent inhibitors of CD2-mediated Ca2+ rise, with one exception probably due to poor affinity. Thus, in addition to being a site of interaction with major histocompatibility complex Class I as recent data have indicated, this region of the CD8 alpha subunit may play a role in regulating T cell activation.

Antibodies, Monoclonal↗

PubMed1993

Signalling through CD28 T-cell activation pathway involves an inositol phospholipid-specific phospholipase C activity.

Stimulation of the human T-cell line, Jurkat, by a monoclonal antibody (mAb) directed against the CD28 molecule leads to sustained increases in intracellular levels of Ca2+ ([Ca2+]i); the initial rise in Ca2+ comes from internal stores, followed by Ca2+ entry into the cells. The CD28 molecule also appears to activate polyphosphoinositide (InsPL)-specific phospholipase C (PLC) activity in Jurkat cells, as demonstrated by PtdInsP2 breakdown, InsP3 and 1,2-diacylglycerol generation and PtdIns resynthesis. We also observed that interleukin-2 (IL2) production induced via CD28 triggering was sensitive to a selective protein kinase C inhibitor. Of the four other anti-CD28 mAbs (CD28.2, CD28.4, CD28.5, CD28.6) tested, only one (CD28.5) was unable to generate any InsPL-specific PLC or IL2 secretion. However, the cross-linking of cell-bound CD28.5 with anti-mouse Ig antibodies led to an increase in [Ca2+]i. CD28-molecule clustering in itself appears to be a sufficient signal for induction of PLC activity.

Antibodies, Monoclonal↗

PubMed1993

Regulation of CD2-mediated human T cell activation: anti-CD8 monoclonal antibodies inhibit CD2-mediated rise in intracellular calcium.

The human CD8 glycoprotein regulates the function of cytotoxic T cells activated by antigenic peptide as well as via CD3 or CD2 mAbs. Activation of T cells by CD2 mAbs requires two mAbs directed against distinct CD2 epitopes and induces tyrosine phosphorylation, PI-PLC activity generating the second messengers, IP3 and DAG, and finally lymphokine secretion. We have investigated the role of the CD8 alpha molecule in CD2-mediated activation of human cytotoxic T cell clones and CD8+ resting T cells. CD8 alpha-specific mAb inhibited 60% of the allospecific cytotoxicity of the CD8+ clone against its target cell and 86% of the CD2-redirected killing against the HLA Class I-negative Daudi target cell. In addition, CD8 alpha-specific mAb inhibited CD2-mediated TNF alpha and IL2 secretion by the CD8+ clone. Furthermore, CD8 alpha-specific mAb inhibited the increase in intracellular ionized calcium mediated by CD2 mAbs in the CD8+ clone and in purified T cells. Since the [Ca2+]i recruitment from internal stores induced by CD2 mAbs was inhibited, the inhibitory effect induced by the CD8 alpha-specific mAb probably acts on the PI-PLC activation pathway. This inhibition mechanism involves neither a decrease in affinity of CD2 mAb for its target nor a decrease in CD2 cell surface expression or a rise in cAMP known as an inhibitor of the CD2-mediated PI-PLC activity. These results suggest that the inhibitory mechanism induced by the CD8 mAb may prevent the activation of the PI-PLC activity, probably through the CD8 alpha-associated protein tyrosine kinase p56lck.

Antibodies, Monoclonal↗

PubMed1993

Anti-T11.1 and -T11.2 monoclonal antibodies play a different role in CD2-mediated signal transduction.

We comparatively evaluated (Ca2+)i mobilization after triggering with a stimulatory pair of CD2 (CD2.9, anti-T11.1 + CD2.1, anti-T11.2) or CD3 mAbs in the differentiated T-cell line Jurkat, using INDO-1 labeling and cytofluorimetry. The results obtained showed different (Ca2+)i mobilization kinetics following CD2 or CD3 stimulation (the former being slower than the latter), not due to different association kinetics of mAbs. In a nonreciprocal manner, however, preliminary interaction with CD2.1 (anti-T11.2) followed by CD2.9 (anti-T11.1) induces a rapid (Ca2+)i rise, similar to CD3 stimulation, as shown by preincubation experiments. There is no interference between CD2.9 and CD2.1 mAb binding. CD2.1 mAb by itself is unable to induce (Ca2+)i mobilization; in addition, preincubation with CD2.1 mAb did not modify the CD2, CD3, CD45, or CD28 immunoprecipitation patterns. Triggering of the epitope recognized by CD2.1 mAb may favor, possibly via conformational changes of CD2 molecule or (Ca2+)i-unrelated metabolic effect(s), optimal signal transduction.

Antibodies, Monoclonal↗