Brown J J, Papaioannou V E
Department of Pathology, Tufts University School of Medicine, Boston, MA 02111.
Development. 1993 Feb;117(2):483-92. doi: 10.1242/dev.117.2.483.
The ontogeny of hyaluronan (HA) secretion during early mouse embryogenesis has been investigated using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is first secreted by visceral endoderm cells of the early egg cylinder on day 5.5 post coitum (p.c.), predominantly into the expanding yolk cavity. On day 6.5 p.c., HA is present in both the yolk and proamniotic cavities, but pericellular staining is restricted to the visceral endoderm and a population of embryonic ectoderm cells at the antimesometrial end of the proamniotic cavity. By the primitive streak stage, HA is secreted into the ectoplacental, exocoelomic, amniotic and yolk cavities, whilst the only cells exhibiting pericellular staining are those of the embryonic and extraembryonic mesoderm, including the allantois. Comparisons of HA-staining patterns of cultured whole blastocysts, microdissected trophectoderm fragments and immunosurgically isolated inner cell masses, revealed no trophoblast-associated HA secretion during outgrowth in vitro but significant synthetic activity by the endodermal derivatives of differentiating inner cell masses. To identify the cell lineages responsible for secretion of HA into the embryonic cavities and to investigate the origin of the HA observed around migrating mesoderm cells, day 7.5 p.c. primitive streak stage conceptuses were dissected into their various embryonic and extraembryonic cell lineages. HA secretion was observed after short-term suspension culture of mesoderm, embryonic ectoderm and embryonic endoderm, but was undetectable in fragments of ectoplacental cone, parietal yolk sac (primary giant trophoblast and parietal endoderm), extraembryonic ectoderm or extraembryonic endoderm. The level of synthesis by the HA-positive tissues was markedly enhanced by culture in medium containing serum, compared with that obtained following culture in medium supplemented with a defined serum substitute containing insulin, transferrin, selenous acid and linoleic acid. This suggests that additional growth factors, present in serum but absent from the serum substitute, are required for optimal HA synthesis by the HA-secreting tissues in vitro, and probably also in vivo. The implications of these events for implantation and the development of peri- and early post-implantation mouse embryos are discussed, and a new role for HA in the initial formation and expansion of the embryonic cavities is proposed.
利用来自软骨蛋白聚糖的生物素标记透明质酸（HA）结合复合物，对小鼠胚胎早期发育过程中HA分泌的个体发生进行了研究。在交配后第5.5天（p.c.），HA首先由早期卵柱的脏内胚层细胞分泌，主要进入不断扩大的卵黄腔。在p.c.第6.5天，HA存在于卵黄腔和羊膜腔中，但细胞周围染色仅限于脏内胚层以及羊膜腔反中胚层端的一群胚胎外胚层细胞。到原条期时，HA分泌到外胎盘、胚外体腔、羊膜腔和卵黄腔中，而唯一呈现细胞周围染色的细胞是胚胎和胚外中胚层细胞，包括尿囊。对培养的完整囊胚、显微切割的滋养外胚层片段和免疫外科分离的内细胞团的HA染色模式进行比较，发现在体外生长过程中，滋养层没有HA分泌，但分化的内细胞团的内胚层衍生物具有显著的合成活性。为了确定负责将HA分泌到胚胎腔中的细胞谱系，并研究在迁移的中胚层细胞周围观察到的HA的来源，将p.c.第7.5天原条期的概念胚胎解剖成各种胚胎和胚外细胞谱系。在对中胚层、胚胎外胚层和胚胎内胚层进行短期悬浮培养后，观察到了HA分泌，但在外胎盘锥、壁层卵黄囊（初级巨大滋养层和壁层内胚层）、胚外外胚层或胚外内胚层的片段中未检测到HA分泌。与在添加了含有胰岛素、转铁蛋白、亚硒酸和亚油酸的特定血清替代品的培养基中培养相比，在含有血清的培养基中培养时，HA阳性组织的合成水平明显提高。这表明血清中存在但血清替代品中不存在的其他生长因子是体外（可能在体内也是）HA分泌组织进行最佳HA合成所必需的。讨论了这些事件对小鼠胚胎着床以及着床周围和着床后早期发育的影响，并提出了HA在胚胎腔初始形成和扩大中的新作用。
