The masking effect of sialic acid on Con A, PNA and SBA ectoderm binding sites during neurulation in the bantam chick embryo

Abstract

The masking effect of sialic acid on cell surface carbohydrates localized on the ectoderm in stage 6-11 bantam embryos was examined using fluorescein isothiocyanate-labeled Con A, PNA, SBA, LFA, and LPA before and after neuraminidase treatment. The results showed selective lectin binding on both the neuroectoderm and the surface ectoderm. In general, these lectin-binding sites increased or were at least expressed on neuroectoderm during neurulation. On the apical surfaces of the developing neuroectoderm, masked Con A-binding sites were evident from the earliest stage and rapidly increased. These sites coexisted with unmasked binding sites which gradually increased. Masked PNA sites were rarely observed but became abundant in later stages, even though coexistent unmasked sites also rapidly increased. Masked SBA sites were poorly observable in the early stage and gradually increased thereafter, whereas unmasked sites were expressed at later stages. On the basal surfaces masked Con A sites were evident in the early stages but gradually decreased in later stages, whereas unmasked sites were relatively abundant and increased thereafter. Masked PNA sites were evident and increased very rapidly, whereas unmasked sites became observable up to the latest stage. Masked SBA sites were minimal in all three stages, and unmasked sites expressed themselves slightly at later stages. The change in composition of carbohydrates on the developing neuroectoderm was obviously different from that on the developing surface ectoderm. On the contact surface of the neural ridge, the number of masked sites of penultimate sugars was large at Con A sites, slight at PNA and SBA sites, which coexisted with unmasked sugar chain terminals in the areas where Con A sites were moderate and where PNA and SBA sites were poor. Finally, the role of masking on binding sites for Con A, PNA and SBA during neural tube closure is discussed, and the observation that the apparent masking effect on three lectin binding sites did not correspond to the content of sialic acid detected by LFA and LPA is a subject for further study.

Combined Bacteria Microarray and Quartz Crystal Microbalance Approach for Exploring Glycosignatures of Nontypeable Haemophilus influenzae and Recognition by Host Lectins

“…Conversely, the absence of sialic acid residues masking Gal or GalNAc groups might explain the significant increase in the binding of SBA, RCA, and VAA. A similar shielding effect of sialic acid on the binding of SBA was reported in cell binding and histochemical studies. , Moreover, it is known that substitutions at position 3 of Gal, as found in NTHi375 LOS, abolish RCA and VAA binding because this is a key position for recognition. , In contrast, MAL-I tolerates substitutions at position 3, sialylation or sulfation even increasing the binding affinity, thus explaining that no increase in the binding to Δ siaB was observed for this lectin, a behavior also exhibited by WFA. Of note, mono- and disialylated species have been reported to represent 9% and 5%, respectively, of the total LOS species in wild type NTHi375, whereas the majority of LOS molecules are expected to display a terminal Gal residue that could be potentially targeted by Gal-specific lectins.…”

“…The strain-binding pattern of ConA was also complex, with enhanced recognition of Δ siaB , Δ lic2A , and Δ lgtF and similar or slightly decreased binding to the strains with shorter LOS versions (Δ lpsA , Δ lgtF Δ lpsA , and Δ opsX ). Increased ConA binding following desialylation was previously reported in histochemical studies, while Δ lic2A and Δ lgtF display terminal Glc and Hep moieties, respectively, that could serve as docking points for ConA, thereby explaining the increased binding to these strains. On the other hand, the small differences in ConA binding to the most truncated strains compared to wild type NTHi375 suggest that other surface carbohydrate structures, besides the LOS, are recognized by ConA.…”

The Lex Carbohydrate Sequence Is Recognized by Antibody to L5, a Functional Antigen in Early Neural Development

“…Appearance of the neural plate coincides with the loss of long-chain linear and branched type 2 antigens i (Den) and I (Step) (Thorpe et al, 1988) and the type 1 structure recognized by FCIO.2 (Loveless et al, 1990); whereas, at the same time, short branched chains such as sialosyl I (Ma) appear to accumulate in the presumptive neural plate. In a similar manner, lectin binding properties of the neuroectoderm change dramatically during neurulation (Curnie et al, 1984;Takahashi and Howes, 1986;Takahashi, 1988Takahashi, , 1992.…”

Glycoconjugate Expression and Cartilage Development of the Cranial Skeleton

“…After enzymatic pretreatment other groups detect PNA-reactive glycoconjugates throughout the mesenchymal tissue ( fig.¤16), displaying a high degree of binding homogeneity [Slack, 1985;Louryan and Glineur, 1991;Zschäbitz et al, 1995a, b]. The most convincing model to interpret these morphological discrepancies is the sialic acid gradient hypothesis [Takahashi, 1992]. Low levels in condensation centers, increasing amounts in 'other areas such as prospective tendons' [Louryan and Glineur, 1991] and high concentrations in loose mesenchymal tissue could explain a corresponding reduction in the sensitivity to neuraminidase pretreatment.…”