Vainio S, Jalkanen M, Bernfield M, Saxén L
Department of Pathology, University of Helsinki, Finland.
Dev Biol. 1992 Aug;152(2):221-32. doi: 10.1016/0012-1606(92)90130-9.
Induction of the embryonic kidney mesenchyme is followed by formation of cell aggregates which subsequently transform into epithelial tubules. Syndecan, which binds various matrix components and growth factors, is a candidate molecule to be involved in this process. We have analyzed the changes in the expression of syndecan during tubule morphogenesis by using in situ hybridization and slot-blot analysis. The expression pattern of syndecan was compared with the distribution of cell proliferation analyzed by immunohistochemistry. Furthermore, the expression of syndecan during formation of the pretubular aggregates was studied in hanging-drop cultures of experimentally induced mesenchymal cells. Syndecan mRNA was expressed in the metanephric mesenchyme prior to induction, was intensely present during formation of the pretubular cell aggregates, but was lost during maturation of the nephron. Slot-blot analyses of the kidney mesenchymes (11-day kidney) cultured in a transfilter situation with a heterotypic inductor tissue that triggers a complete tubulogenic program in the nephric mesenchyme during the first 24 hr suggested the presence of syndecan mRNA in the uninduced mesenchymes with no change during induction. Expression of mRNA was stimulated later (13-day kidney) followed by subsequent decrease. Immunoisolation of sulfate-labeled syndecan, however, revealed a marked stimulation in the induced kidney mesenchyme during the first 24-hr inductive period when the DNA level still remained constant. In hanging-drop cultures where either induced or uninduced mesenchymal cells were dissociated and reaggregated, syndecan was detected only in the induced and aggregating mesenchymal cells. Double-immunostaining demonstrated a close correlation between syndecan expression and cell proliferation analyzed by bromodeoxyuridine incorporation. Thus, it appears that syndecan expression in the mesenchyme is initially induced post-transcriptionally and later during differentiation at the mRNA level. Syndecan may have a dual function during early kidney morphogenesis; it may be involved in cell aggregation through its adhesive properties, and it may contribute to proliferation of the induced mesenchymal cells by binding growth factors.
胚胎肾间充质诱导后会形成细胞聚集体，这些聚集体随后会转变为上皮小管。Syndecan能结合多种基质成分和生长因子，是参与这一过程的候选分子。我们通过原位杂交和狭缝印迹分析，研究了小管形态发生过程中Syndecan表达的变化。将Syndecan的表达模式与通过免疫组织化学分析的细胞增殖分布进行了比较。此外，在实验诱导的间充质细胞的悬滴培养中，研究了Syndecan在肾小管前聚集体形成过程中的表达。Syndecan mRNA在诱导前的后肾间充质中表达，在肾小管前体细胞聚集体形成过程中大量存在，但在肾单位成熟过程中消失。对在跨滤器条件下与异型诱导组织共同培养的肾间充质（11天龄肾脏）进行狭缝印迹分析，该异型诱导组织在前24小时内触发肾间充质的完整肾小管形成程序，结果表明未诱导的间充质中存在Syndecan mRNA，诱导过程中无变化。mRNA表达随后（13天龄肾脏）受到刺激，随后下降。然而，硫酸化标记的Syndecan的免疫分离显示，在诱导的前24小时诱导期内，诱导的肾间充质中有明显的刺激，此时DNA水平仍保持恒定。在诱导或未诱导的间充质细胞解离并重新聚集的悬滴培养中，仅在诱导和聚集的间充质细胞中检测到Syndecan。双重免疫染色显示，Syndecan表达与通过溴脱氧尿苷掺入分析的细胞增殖密切相关。因此，间充质中Syndecan的表达似乎最初是在转录后诱导的，后来在分化过程中在mRNA水平上诱导。Syndecan在早期肾脏形态发生过程中可能具有双重功能；它可能通过其黏附特性参与细胞聚集，并可能通过结合生长因子促进诱导的间充质细胞增殖。
