US-GLOBEC: Analysis of short-term growth in copepods and larval fish using molecular markers of cell proliferation

INVESTIGATORS:

John J. Stegeman, Senior Scientist,
Michael J. Moore, Research Specialist,
Bruce R. Woodin, Research Associate,
Michael S. Morss, Guest Student.

Biology Department
Woods Hole Oceanographic Institution
Woods Hole, MA 02543-1049
jstegeman@whoi.edu
mmoore@whoi.edu

GRANT PERIOD: 1 September 1993 to 31 August 1996

STATEMENT OF OBJECTIVES:

This study addresses the following goals of the US-GLOBEC Georges Bank Study:

  1. To measure vital rates of target species relating to population dynamics

  2. To measure the vital rates of target species in the context of the physical processes which influence vertical mixing and seasonal stratification of the water column.

  3. To study how microscale turbulence interacts with micro-patchiness to affect predator-prey interactions and vital rates.

The specific project goals are:

  1. Establish functional molecular markers of cell proliferation in juvenile and adult copepods and larval cod and haddock.

  2. Establish which organs or tissues in the above animals have measurable increases in cell proliferation during body growth that are predictive of growth of the whole organism.

  3. Compare a) the cell proliferation growth index (CPGI) with other commonly used indices of growth such as size, weight, egg production and RNA/DNA ratios by collaborating as necessary, and b) the influence of temperature and food availability on copepod and larval fish growth using the CPGI.

  4. Further optimize the CPGI methodology to establish a robust and rapid shipboard assay for growth in larval fish and copepods.

  5. Utilize the field method to compare growth in larval fish and copepods between areas of low and high productivity, comparing the effects of physical and biological parameters, such as temperature, stratification, mixing, and food availability on the CPGI and compare growth between groups of organisms at the micro-patch scale.

  6. Examine cell proliferation in predators, such as Cyanea sp. to establish the changes in growth rate resulting from altered predation rates, as assessed by dietary studies.

  7. Utilize available histological samples to assess the impact of chemical contaminants and infectious disease on the growth and survival of larval cod and haddock.

STATEMENT OF WORK:

Goal 1. Establish functional molecular markers of cell proliferation in juvenile and adult copepods and larval cod and haddock. We have two immunohistochemical markers for cell proliferation in these organisms.

Quantitation of immunohistochemistry--PCNA and BrdU labelling indices are estimated for each cell type present in each specimen. PCNA expression is either calculated as a ratio of the number of labelled nuclei per 1000 nuclei (labelling index) or estimated as a semi-quantitative index. For the labelling index one thousand nuclei are examined for each cell type in each specimen, except in cases where the total number of nuclei of a particular cell type was less in the available section. In those cases the index is normalized to a fraction of 1000. PCNA expression and BrdU incorporation can also be estimated on a score of 0 (absent) through 4 (very common).

Goal 2. Establish which organs or tissues in copepods and larval fish have measurable increases in cell proliferation during body growth that are predictive of growth of the whole organism.

These methods have shown high levels of proliferation in the pancreas, liver, intestine and integument of larval cod and winter flounder. The intestinal contents appear not to give any reactivity with the PC 10 antibody suggesting that prey items should not interfere with whole organism nuclear extracts as used in the slot blot assay. In copepodites we have seen proliferation in the caudal region of the cephalothorax and the appendages, and in adults gonadal maturation is the most active proliferative event. PCNA expression in C5 and adult females was higher than in males. The low level of PCNA in males as compared to the other two classes is remarkable and presumably reflects the greater growth investment in eggs than sperm.

Goal 3. Compare a) the cell proliferation growth index (CPGI) with other commonly used indices of growth such as size, weight, egg production and RNA/DNA ratios by collaborating as necessary, and b) the influence of temperature and food availability on copepod and larval fish growth using the CPGI.

This goal is still being actively pursued. In collaboration with Scott Gallager and Phil Alatalo here at WHOI Pseudodiaptomus coronatus copepodites were reared at two temperatures, and either fed or starved. Larval codfish were reared on three different diets. Proliferation indices were compared with physical measurements made at the time of sampling. PCNA expression was found to be significantly elevated on a diet of nauplii as compared to a mixed diet, or the initial condition. We have also completed data generation from a series of experiments conducted in parallel with Dr.'s Clarke, Huntley, Lopez and Crawford in Hawaii. PCNA expression does appear to correlate with feeding regime in a manner comparable to citrate synthase, whereas PCNA expression did not correlate with egg productivity. This presumably reflects a mismatch in the timing of PCNA expression during gonadal differentiation vs. the actual shedding of mature eggs.

Goal 4. Further optimize the CPGI methodology to establish a robust and rapid shipboard assay for growth in larval fish and copepods.

We have expended substantial effort in developing this assay with considerable success. For individual larval fish, and 1-5 copepods, depending on size, we have developed an in vitro assay for PCNA content on frozen samples. The method was first established using a western blot technique, and is now routinely run 40 samples at a time, using a slot blot technique, as described above. Samples are homogenized in a buffer, centrifuged to remove cell debris, and applied to a slot blot apparatus. Blots are then visualized using a chemiluminescence method, with digital quantitation. This method has been successfully applied both in larval cod and winter flounder, Pseudodiaptomus coronatus, and a number of copepod species and crab zoae from Hawaii.

We are also currently evaluating other cell cycle associated proteins for potential application in this project. In particular we will determine which proteins might have a shorter half life than PCNA and thus be sensitive to short term changes in environmental conditions.

Goal 5. Utilize the field method to compare growth in larval fish and copepods between areas of low and high productivity, comparing the effects of physical and biological parameters, such as temperature, stratification, mixing, and food availability on the CPGI and compare growth between groups of organisms at the micro-patch scale.

We participated in three US-GLOBEC cruises aboard the R/V Seward Johnson in the Spring of 1995 (SJ-9503, SJ-9505, SJ-9507). A total of 1457 individual samples of larval cod and haddock, and adult female Calanus finmarchicus were preserved in either liquid nitrogen or formalin for slot blot and immunohistochemical analysis respectively. These analyses are underway at present.

Goal 6. Examine cell proliferation in predators, such as Cyanea sp. to establish the changes in growth rate resulting from altered predation rates, as assessed by dietary studies.

This goal will be pursued as time allows in the coming year.

Goal 7. Utilize available histological samples to assess the impact of chemical contaminants and infectious disease on the growth and survival of larval cod and haddock.

This important question has not been addressed to date in the two target species, but we can report some important observations in another Georges Bank groundfish species, the winter flounder (Pleuronectes americanus). In other studies we have shown a strong correlation between exposure to persistent halogenated hydrocarbons, and the presence of hydropically vacuolated cells in the liver of this species. These cells have been shown to have increased proliferative activity. In a comparison of cell proliferation, chemical exposure, prevalence of vacuolation and water temperature at the time of collection, it appeared the strongest correlation was between cell proliferation and water temperature. Thus climate change as evidenced by changes in water temperature has the potential to be a significant factor in the physiology and pathology of this species at least, even in areas where chemical exposure is also of known significance.

PUBLICATIONS

We have a paper describing the BrdU technique (Moore et al., 1994), and we have a manuscript in revision describing use of BrdU and PCNA in copepodites, and will be preparing a manuscript describing the relationship between feeding and PCNA expression shortly.

SUMMARY OF KEY FINDINGS:

We have completed the majority of our goals through analysis of experimental material generated at WHOI and of field material in collaboration with a number of GLOBEC projects at the copepod workshop held at the Hawaii Institute of Marine Biology in May 1994. We have also made substantive progress in the major field aim of the project through participation in 3 US-GLOBEC cruises on Georges Bank in March, April and May 1995. The markers we have developed are applicable to a broad spectrum of marine life. We have found that cell proliferation is in general increased with improved nutrition in copepods and larval fish. We have observed that copepodites put most of their growth into the growing caudal segment, whereas adults appear to invest more in gonadal maturation, even in periods of relative starvation. We have found that water temperature appears to be a greater determinant of cell proliferation activity than chemical exposure. We therefore believe we have developed a short term index that reflects both somatic growth in larval fish and subadult copepods and reproductive effort in mature copepods. This is an important development for our capacity to directly assess biological productivity in the ocean. Tools such as these that detect cells undergoing division are central to the study of the effects of alterations in temperature, UV light exposure, food availability and other climatically influenced variables in many if not all organisms in the oceans of the world.

ACKNOWLEDGMENTS

We are grateful to Carolyn Miller, Phil Alatalo, Scott Gallager, Mark Huntley, Mai Lopez and Greg Lough.

REFERENCES CITED

Kloepper-Sams, P.J., Park, S.S., Gelboin, H.V., Stegeman, J.J. 1987. Specificity and cross-reactivity of monoclonal and polyclonal antibodies against cytochrome P450E of the marine fish scup. Arch. Biochem. Biophys. 253: 268-278.

Smith, P.K., Krohn, R.I., Hermanson, G.T., Mallia, A.K., Gartner, F.H., Provenzano, M.D., Fujimoto, E.K., Goeke, N.M., Olson, B.J., Klenk, D.C. 1985. Measurement of protein using bicinchoninic acid. Anal. Biochem. 150: 76-85.

Ortego, L., Hawkins, W., Walker, W., Krol, R., Benson, W. In press. Detection of proliferating cell nuclear antigen (PCNA) in tissues of 3 small fish species. Biotechnic and Histochemistry

Ellwart, J., Dormer, P. 1985. Effect of 5-fluoro-2'-deoxyuridine (FdUrd) on 5-bromo-2'-deoxyuridine (BrdUrd) incorporation into DNA measured with a monoclonal BrdUrd antibody and by the BrdU/Hoechst quenching effect. Cytometry 6: 513-520.

Moore, M.J., Stegeman, J.J. 1992. Bromodeoxyuridine uptake in hydropic vacuolation and neoplasms in winter flounder liver. Marine Environmental Research 34: 13-18.

Moore, M.J., Leavitt, D.F., Shumate, A.M., Alatalo, P., Stegeman, J.J. 1994. A cell proliferation assay for small fish and aquatic invertebrates using bath exposure to bromodeoxyuridine. Aquat Toxicol 30: 183-188.