Microinjection of lectins, hyaluronidase, and hyaluronate fragments interferes with cleavage delay and mesoderm induction in embryos of Patella vulgata.

In embryos of Patella vulgata at the 32-cell stage, one of the four vegetally located macromeres makes contacts with overlying animal micromeres. As a result, this macromere (designated 3D) divides significantly later than the other macromeres and forms the mesodermal stem cell 4d. Shortly before and during this interaction two types of extracellular matrix are present: a basal lamina-like layer on the tips of the micromeres and a loose fibrillar meshwork in the blastocoel. In this paper we examine the role of the matrix in cleavage delay and mesoderm determination. The microinjection of extracellular matrix-binding lectins, or of hyaluronidase, or of decasaccharide fragments of hyaluronate into the blastocoel results in embryos in which either no or two macromeres are delayed in cleavage and are presumably determined as mesodermal stem cells. We suggest that the fibrillar meshwork is needed for macromere elongation toward the micromeres and that the basal lamina-like layer is involved in the determination process itself.

Composition of the nucleotides pool in a morphogenetic compartment in eggs of Nassarius reticulatus (Mollusca) analysed by capillary isotachophoresis.

The spectrum of low molecular weight compounds, in particular of ribonucleotides, within first cleavage stage embryos of the polar lobe-forming mollusc Nassarius reticulatus and the distribution of the compounds within the embryo at the trefoil stage of first cleavage are analysed by means of capillary isotachophoresis after 0.5 M PCA extraction. The compounds which are found in the whole trefoil embryo (T), the lobeless part (LL), and the polar lobe (PL) respectively, and the mean quantities (nmol. microliter-1; n = 6) are: UTP (11.5, 4.8, 5.6), ITP (8.5, 3.6, 5.0), GTP (10.3, 3.0, 9.0), ATP (29.8, 13.4, 18.8), UDP (11.8, 3.4, 8.7), CTP (8.0, 3.1, 4.5), GDP (5.3, 2.6, 3.4), ADP (16.5, 6.1, 11.6), CDP (4.0, 1.4, 2.6), GMP (4.7, 2.7, 4.3), glucose-6-phosphate (G6P) (53.5, 38.8, 13.0). These compounds appear to be localized in the non-yolk cytoplasmic pool. As the volume ratio of PL/LL for total volume and for non-yolk cytoplasmic volume is about 0.74 and 0.60 respectively, the concentration of all nucleotides in PL as compared to LL is significantly higher (HO, p less than 0.001), both relative to the total volume and to the non-yolk cytoplasmic volume. The G6P concentration is considerably higher in the lobeless part. The morphogenetic role of the vegetal pole compartment of the egg apparently is correlated with a relatively high level of its nucleotide contents.