Expression of univin, a TGF-β growth factor, requires ectoderm–ECM interaction and promotes skeletal growth in the sea urchin embryo

Abstract

Pl-nectin is an ECM protein located on the apical surface of ectoderm cells of Paracentrotus lividus sea urchin embryo. Inhibition of ECM-ectoderm cell interaction by the addition of McAb to Pl-nectin to the culture causes a dramatic impairment of skeletogenesis, offering a good model for the study of factor(s) involved in skeleton elongation and patterning. We showed that skeleton deficiency was not due to a reduction in the number of PMCs ingressing the blastocoel, but it was correlated with a reduction in the number of Pl-SM30-expressing PMCs. Here, we provide evidence on the involvement of growth factor(s) in skeleton morphogenesis. Skeleton-defective embryos showed a strong reduction in the levels of expression of Pl-univin, a growth factor of the TGF-beta superfamily, which was correlated with an equivalent strong reduction in the levels of Pl-SM30. In contrast, expression levels of Pl-BMP5-7 remained low and constant in both skeleton-defective and normal embryos. Microinjection of horse serum in the blastocoelic cavity of embryos cultured in the presence of the antibody rescued skeleton development. Finally, we found that misexpression of univin is also sufficient to rescue defects in skeleton elongation and SM30 expression caused by McAb to Pl-nectin, suggesting a key role for univin or closely related factor in sea urchin skeleton morphogenesis.

Nodal/activin signaling establishes oral–aboral polarity in the early sea urchin embryo

“…BMP2/4 signaling acts to repress aboral genes in the oral ectoderm territory; however, BMP2/4 overexpression prevents the expression of only a subset of aboral genes and does not uniformly oralize the embryo (Gross et al, 2003). Univin (Stenzel et al, 1994) has been shown recently to play a role in skeletal rod growth (Zito et al, 2003), whereas BMP5/7 (Ponce et al, 1999) has yet to be assigned a function in this embryo.…”

Stress response gene activation protects sea urchin embryos exposed to X-rays

“…A single-step reverse transcriptionpolymerase chain reaction (RT-PCR) was carried out using SuperScript One-Step RT-PCR kit (Invitrogen). Three cDNA fragments were amplified from total RNA having the following size: 180nt-hsp70, 327nt-p63, and 248nt-S24, with the latter used as internal reference (Zito et al 2003). The primers amplifying hsp70 cDNA fragment were previously described (Bonaventura et al 2006).…”

Afuni, a novel transforming growth factor-β gene is involved in arm regeneration by the brittle star Amphiura filiformis

“…To date, the full-coding sequence for a univin gene has only been isolated from S. purpuratus. A gene fragment of around 250 bases, with high-sequence similarity to part of the C-terminal region of univin, has been isolated from another sea urchin, P. lividis (Zito et al 2003). This gene has been excluded from figures and tables, as only part of the C-terminal sequence is known.…”

“…It therefore seems likely that afuni plays a role in the normal somatic growth of the arm. The microinjection studies conducted by Zito et al (2003) implicated univin as a key factor in the skeletogenesis of P. lividus embryos. It must be considered that afuni may be playing a similar role in ophiuroid arm regeneration.…”

“…At gastrulation, univin expression is restricted to the foregut and ciliated band. In later functional studies, microinjection of synthetic univin mRNA into Paracentrotus lividus embryos rescued defects in skeleton elongation caused by interfering with cell-extracellular matrix (ECM) interactions engineered by blocking nectin with a monoclonal antibody (Zito et al 2003). More recently, members of the BMP2/4 (Angerer et al 2000) and BMP5/8 (Ponce et al 1999) subfamilies have been cloned from sea urchin.…”