Ruffins S W, Ettensohn C A
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Development. 1996 Jan;122(1):253-63. doi: 10.1242/dev.122.1.253.
Previous lineage tracing experiments have shown that the vegetal blastomers of cleavage stage embryos give rise to all the mesoderm and endoderm of the sea urchin larva. In these studies, vegetal blastomers were labeled no later than the sixth cleavage division (60-64 cell stage). In an earlier study we showed that single cells in the vegetal plate of the blastula stage Lytechinus variegatus embryo could be labeled in situ with the fluorescent, lipophilic dye, DiI(C18), and that cells labeled in the central region of the vegetal plate of the mesenchyme blastula primarily gave rise to homogeneous clones consisting of a single secondary mesenchyme cell (SMC) type (Ruffins and Ettensohn (1993) Dev. Biol. 160, 285-288). Our clonal labeling showed that a detailed fate map could be generated using the DiI(C18) labeling technique. Such a fate map could provide information about the spatial relationships between the precursors of specific mesodermal and endodermal cell types and information concerning the movements of these cells during gastrulation and later embryogenesis. We have used this method to construct the first detailed fate map of the vegetal plate of the sea urchin embryo. Ours is a latitudinal map; mapping from the plate center, where the mesodermal precursors reside, through the region which contains the endodermal precursors and across the ectodermal boundary. We found that the precursors of certain SMC types are segregated in the mesenchyme blastula stage vegetal plate and that prospective germ layers reside within specific boundaries. To determine whether the vegetal plate is radially symmetrical with respect to mesodermal cell fates, single blastomeres of four cell stage embryos were injected with lysyl-rhodamine dextran (LRD). The resulting ectodermal labeling patterns were classified and correlated with the SMC types labeled. This analysis indicates that the dorsal and ventral blastomers do not contribute equally to SMC derivatives in L. variegatus.
先前的谱系追踪实验表明，卵裂期胚胎的植物极卵裂球会发育成海胆幼虫的所有中胚层和内胚层。在这些研究中，植物极卵裂球最迟在第六次卵裂时（60 - 64细胞期）被标记。在早期的一项研究中，我们表明，囊胚期的多棘海胆胚胎植物极板中的单个细胞可以用亲脂性荧光染料DiI（C18）进行原位标记，并且在间充质囊胚植物极板中央区域标记的细胞主要产生由单一类型的次生间充质细胞（SMC）组成的同质克隆（鲁芬斯和埃滕索恩（1993年）《发育生物学》160，285 - 288页）。我们的克隆标记表明，使用DiI（C18）标记技术可以生成详细的命运图谱。这样的命运图谱可以提供特定中胚层和内胚层细胞类型前体之间的空间关系信息，以及这些细胞在原肠胚形成和后期胚胎发育过程中的运动信息。我们已经使用这种方法构建了海胆胚胎植物极板的第一张详细命运图谱。我们的图谱是横向图谱；从含有中胚层前体的极板中心开始绘制，穿过包含内胚层前体的区域并跨越外胚层边界。我们发现，某些类型的SMC前体在间充质囊胚期植物极板中是分离的，并且预期的胚层位于特定边界内。为了确定植物极板在中胚层细胞命运方面是否呈径向对称，向四细胞期胚胎的单个卵裂球注射赖氨酰罗丹明葡聚糖（LRD）。对产生的外胚层标记模式进行分类，并与标记的SMC类型相关联。该分析表明，在多棘海胆中，背侧和腹侧卵裂球对SMC衍生物的贡献并不相同。
