Differential localization of [35S] sulfate within ectodermal basement membrane in relation to initiation of chick limb buds.

This study examined the possible developmental relationship between differential amounts of glycosaminoglycans (GAG) within the ectodermal basement membrane and initiation of limb outgrowth. Chick embryos at stages 11-20 were labeled in ovo with 35SO4 and processed for autoradiography. After exposure to sulfate for 15 min. The label was localized within the surface ectoderm whereas after 3 h the label was localized within the subjacent basement membrane. The label was sensitive to chondroitinase ABC. These experiments suggest that the labeled material was ectodermally derived chondroitin sulfate. At all stages, examined, intense labeling of the basement membrane was associated with relatively undifferentiated, mitotically active tissue, e.g. limb-bud mesoderm. The labeling was less intense in regions with decreased mitotic activity, e.g. the flank. Thus, the labeling pattern of the basement membrane correlated with differential mitotic rates presumed to be associated with limb outgrowth. These observations support the hypothesis that communication between tissues of different origin resulting in altered mitotic behavior of limb and flank mesenchymal cells is facilitated by the ectodermal basement membrane.