Structural and functional comparison of 15S- and 15R-specific cyclooxygenases from the coral Plexaura homomalla.

It has been known for 30 years that the gorgonian coral Plexaura homomalla contains either 15S- or 15R-configuration prostaglandins (PGs), depending on its location in the Caribbean. Recently we showed that the 15R-PGs in the R-variety of P. homomalla are formed by a unique cyclooxygenase (COX) with 15R oxygenation specificity [Valmsen, K., J?rving, I., Boeglin, W.E., Varvas, K., Koljak, R., Pehk, T., Brash, A.R. & Samel, N. (2001) Proc. Natl. Acad. Sci. USA98, 7700]. Here we describe the cloning and characterization of a closely related COX protein (97% amino acid sequence identity) from the S-variety of P. homomalla. Functional expression of the S-variant COX cDNA in Sf9 insect cells followed by incubation with exogenous arachidonic acid resulted in formation of PG products with > 98% 15S-configuration. Mutational analysis was performed on a suggested active site determinant of C-15 oxygenation specificity, position 349 (Val in all S-specific COX, Ile in 15R-COX). The 15S-COX Val349 to Ile mutant formed 35% 15R-PGs, while the reverse mutation in the 15R-COX (Ile349Val) led to formation of 70% 15S-products. This establishes position 349 as an important determinant of the product stereochemistry at C-15. Our characterization of the enzyme variants demonstrates that very minor sequence divergence accounts for the content of epimeric PGs in the two variants of P. homomalla and that the differences do not arise by isomerization of the products.     

Mice carrying a conditional Serca2 allele for the generation of Ca handling-deficient mouse models

Sarco(endo)plasmic reticulum calcium ATPases (SERCA) are cellular pumps that transport Ca²⁺ into the sarcoplasmic reticulum (SR). Serca2 is the most widely expressed gene family member. The very early embryonic lethality of Serca2^null mouse embryos has precluded further evaluation of loss of Serca2 function in the context of organ physiology. We have generated mice carrying a conditional Serca2^flox allele which allows disruption of the Serca2 gene in an organ-specific and/or inducible manner. The model was tested by mating Serca2^flox mice with MLC-2v^wt/Cre mice and with αMHC-Cre transgenic mice. In heterozygous Serca2^wt/floxMLC-2v^wt/Cre mice, the expression of SERCA2a and SERCA2b proteins were reduced in the heart and slow skeletal muscle, in accordance with the expression pattern of the MLC-2v gene. In Serca2^flox/flox Tg(αMHC-Cre) embryos with early homozygous cardiac Serca2 disruption, normal embryonic development and yolk sac circulation was maintained up to at least embryonic stage E10.5. The Serca2^flox mouse is the first murine conditional gene disruption model for the SERCA family of Ca²⁺ ATPases, and should be a powerful tool for investigating specific physiological roles of SERCA2 function in a range of tissues and organs in vivo both in adult and embryonic stages.     

Reindeer antlers: visual indicators of individual quality?

Fluctuating asymmetry (FA) in ornamental characters may reflect developmental stability in the translation from genotype to phenotype. Antlers of reindeer show FA, are visually conspicuous ornaments and are important in intraspecific assessment. We show that there is a negative relationship between size and asymmetry in visual antler characteristics (i.e., antler length and number of tines) among free-ranging male reindeer in rut. This indicates that individuals that develop large ornaments are better able to buffer developmental stress than individuals that develop small ornaments. There is no relationship between asymmetry in antler length and asymmetry in jaw length, suggesting that symmetry in antlers does not reflect overall body symmetry. This difference may be caused by trait-specific sensitivity to developmental stress. Such stress may partly be caused by parasites, which show a positive association with asymmetry in antlers, but no relationship to asymmetry in jaws. Our results indicate that antlers may be exposed to directional selection in a visual signaler-receiver system and that information about parasite burden may be obtained from evaluation of asymmetry in antlers developed under exposure to a multitude of environmental stresses. Received: 8 October 1996 / Accepted: 13 January 1997     

Genetic algebras and time continuous models

It is shown how linear genetic algebras, ordinarily applied in situations with discrete time, will also simplify certain systems of differential equations in time continuous models. These models describe the variation of genotype frequencies in infinite populations in different mating systems. The cases considered include matings between individuals randomly drawn from the population at each moment, a population which is continuously backcrossed to a second, constant population, and a population divided into two age groups, which take part in the matings with different intensities. For the first case the general theory is applied to an example with tetraploids having a mixture of chromatid and chromosome segregation.