Temporal-spatial expression of two Paracentrotus lividus cell surface proteins

Bep4 Protein Is Involved in Patterning along the Animal–Vegetal Axis in the Paracentrotus lividus Embryo

In sea urchin embryos, the initial animal-vegetal (AV) axis is specified during oogenesis but the mechanism is largely unknown. By using chemical reagents such as lithium, it is possible to shift the principal embryonic territories toward a vegetal fate. We have investigated the possibility of obtaining the same morphological effect as with lithium by utilizing Fabs against the maternal Bep4 protein that is localized in the animal part of Paracentrotus lividus egg and embryos. Incubation of fertilized eggs with Fabs against Bep4 protein causes exogastrulation at 48 h of development of P. lividus embryos, similar to embryos treated with lithium. This vegetalizing effect was ascertained by utilizing territorial markers such as EctoV, EndoI, and Ig8. The effect of Fabs against Bep4 on gene expression was observed by monitoring spatial expression of the hatching enzyme gene. A decreased expression domain compared to its normal spatial distribution was detected and this effect was again comparable to those obtained with lithium treatment. Association of Bep4 with a cadherin was demonstrated by immunoprecipitation and immunostaining experiments, and an involvement in cell signaling is discussed. In addition, treatment of embryos with anti-Bep4 Fabs causes an enhancement in the level and an expansion in the pattern of nuclear beta-catenin. Moreover, this treatment also provokes a decrease of beta-catenin in adherens junctions. Together, these data indicate that anti-Bep4 Fabs provoke a shift of the animal-vegetal boundary toward the animal pole and suggest an active role of Bep4 protein in patterning along the AV axis.

Asymmetrical localization and segregation of Paracentrotus lividus Bep4 maternal protein

Asymmetric divisions that produce two distinct cells play a fundamental role in generating different cell types during development. Here we investigate the role of the cortex region and mitotic apparatus in asymmetrical localization and segregation of Bep4 protein in Paracentrotus lividus egg. By centrifugation of eggs with or without drugs we established an involvement of the cortex region in localization of Bep4 protein, confirmed by immunohistochemistry of isolated cortex. Association with the mitotic apparatus during cell division permits selective partitioning of Bep4 protein into the daughter cells. Direct association with spindle was also demonstrated both by Western blot and immunohistochemistry after isolation of the mitotic apparatus.