A new invertebrate member of the p53 gene family is developmentally expressed and responds to polychlorinated biphenyls.

The cell-cycle checkpoint protein p53 both directs terminal differentiation and protects embryos from DNA damage. To study invertebrate p53 during early development, we identified three differentially expressed p53 family members (p53, p97, p120) in the surf clam, Spisula solidissima. In these mollusks, p53 and p97 occur in both embryonic and adult tissue, whereas p120 is exclusively embryonic. We sequenced, cloned, and characterized p120 cDNA. The predicted protein, p120, resembles p53 across all evolutionarily conserved regions and contains a C-terminal extension with a sterile alpha motif (SAM) as in p63 and p73. These vertebrate forms of p53 are required for normal inflammatory, epithelial, and neuronal development. Unlike clam p53 and p97, p120 mRNA and protein levels are temporally expressed in embryos, with mRNA levels decreasing with increasing p120 protein (R(2) = 0.97). Highest surf clam p120 mRNA levels coincide with the onset of neuronal growth. In earlier work we have shown that neuronal development is altered by exposure to polychlorinated biphenyls (PCBs), a neurotoxic environmental contaminant. In this study we show that PCBs differentially affect expression of the three surf clam p53 family members. p120 mRNA and protein are reduced the most and earliest in development, p97 protein shows a smaller and later reduction, and p53 protein levels do not change. For the first time we report that unlike p53 and p97, p120 is specifically embryonic and expressed in a time-dependent manner. Furthermore, p120 responds to PCBs by 48 hr when PCB-induced suppression of the serotonergic nervous system occurs

Metallothionein mRNA and protein response to arsenite in juvenile winter flounder, {\it Pleuronectes americanus\/}

The metal-inducible protein, metallothionein (MT), plays an important role in metal homeostasis and detoxification in fish and is a good biomarker candidate of metal impact. Long Island Sound (LIS) winter flounder (Pleuronectes americanus) contain elevated levels of potentially toxic metals. A new PCR-based technique was developed which identified differential MT mRNA responses between adult and juvenile winter flounder exposed to water-borne CdCl\sb2. Subcutaneous exposure of juveniles to NaAs\sp{3+} ranging from sublethal doses to the LD40 significantly elevated MT regardless of baseline variation in liver MT and metal content. The reduced variance associated with MT measurements makes it a more sensitive indicator of sublethal NaAs\sp{3+} exposure than liver As accumulation.^ Saturation of the MT response was linked to mortality by correlating the MT dose response maximum to total liver As content. The upper limit of this response ($\sim$200 ug/g liver) provides a framework for evaluating metal-induced stress among juvenile winter flounder. Fish with high levels of pre-existing MT ($\u3e$100 ug/g) exhibited a narrower MT response window such that MT reached a maximum faster than fish with lower levels of pre-existing MT ($\u3c$75 ug/g). Pre-existing MT correlated with liver Zn content while metal-induced MT correlated with the exposed metal (Cd or As). This suggests that stress effects may be separated from metal-induced MT in the field by measuring both liver MT and Zn.^ The potency of MT induction reflects metal toxicity and this was demonstrated by the stronger MT protein response to CdCl\sb 2, than NaAs\sp{3+}. The continued rise in MT mRNA after the MT protein reached a maximum suggests this parameter is a better short-term indicator of high NaAs\sp{3+} exposure. Exposure to sublethal doses of NaAs\sp{3+} did not significantly elevate liver As content and even very high levels of exposure caused only a transient liver As accumulation. More work is needed to determine whether MT protein remains elevated after liver As returns to baseline. The environmental relevance of MT induction by NaAs\sp{3+} and its associations with liver As content can not be determined until liver As is speciated in both baseline and metal-exposed LIS winter flounder.