The dynamic nature of mollusc egg surface architecture and its relation to the microtubule network

Abstract

Dynamic changes in the surface architecture pattern of embryos of the slipper limpet (Crepidula fornicata, Mollusca) were found in this study to correlate with the dynamic activity and pattern of the underlying mitotic spindle microtubule network, revealed by fluorescent labelling and confocal imaging techniques. Examination of a series of optical sections indicate that this network appears to be spatially co-ordinated together as a whole throughout the embryo. The microtubule pattern also associated with abnormal multipolar spindles resulting from an applied static magnetic field, indicating that the pattern may be generated by a natural endogenous field source. The patterning characteristics of the surface and microtubule network together provide further morphological evidence for a primary morphogenetic or developmental field system which organises the primary body axis and co-ordinates the pattern of cleavage.

Doubly Uniparental Inheritance of Mitochondria As a Model System for Studying Germ Line Formation

“…In this context, M-type mitochondria may be recognized by specific motor proteins that would carry them to the central spindle, where the cleavage furrow of the 2-cell stage forms. The midbody appears to have a role in positioning M-type mitochondria in a stable zygote area on the a-v axis, avoiding a complete dispersal in the blastomeres: in spiral segmentation this central zone is not directly involved in the cleavages, which take place around it [103], so that the mitochondrial aggregation can be maintained. As clearly shown in 4-blastomere embryos of R. philippinarum , the new spindles form in tangential directions, far from the region on the a-v axis where the aggregate of M-type mitochondria is located (Figures 9 and 10).…”

Allocation of cytoplasm to macromeres in embryos of annelids and molluscs is positively correlated with egg size

“…Second, during early asymmetric cleavages in spiralians, one aster of the spindle is positioned immediately adjacent to the cell cortex at the animal pole; indeed, that aster is apparently tightly attached to the cortex. This is true for maturation divisions (Conklin ; Lutz et al ; Dan and Tanaka ), as well as 3rd cleavage (Tyler and Kimber ). Close association of one aster with the animal pole cell cortex may be a basic feature of 3rd–6th cleavages in spiralians.…”