Uroporphyrinogen 3 cosynthetase activity in the fox squirrel (Sciurus niger)

Evolutionary physiology at 30+: Has the promise been fulfilled?: Advances in Evolutionary Physiology: Advances in Evolutionary Physiology

Three decades ago, interactions between evolutionary biology and physiology gave rise to evolutionary physiology. This caused comparative physiologists to improve their research methods by incorporating evolutionary thinking. Simultaneously, evolutionary biologists began focusing more on physiological mechanisms that may help to explain constraints on and trade-offs during microevolutionary processes, as well as macroevolutionary patterns in physiological diversity. Here we argue that evolutionary physiology has yet to reach its full potential, and propose new avenues that may lead to unexpected advances. Viewing physiological adaptations in wild animals as potential solutions to human diseases offers enormous possibilities for biomedicine. New evidence of epigenetic modifications as mechanisms of phenotypic plasticity that regulate physiological traits may also arise in coming years, which may also represent an overlooked enhancer of adaptation via natural selection to explain physiological evolution. Synergistic interactions at these intersections and other areas will lead to a novel understanding of organismal biology.

Models for human porphyrias: Have animals in the wild been overlooked?: Some birds and mammals accumulate significant amounts of porphyrins in the body without showing the injurious symptoms observed in human porphyrias

Humans accumulate porphyrins in the body mostly during the course of porphyrias, diseases caused by defects in the enzymes of the heme biosynthesis pathway and that produce acute attacks, skin lesions and liver cancer. In contrast, some wild mammals and birds are adapted to accumulate porphyrins without injurious consequences. Here we propose viewing such physiological adaptations as potential solutions to human porphyrias, and suggest certain wild animals as models. Given the enzymatic activity and/or the patterns of porphyrin excretion and accumulation, the fox squirrel, the great bustard and the Eurasian eagle owl may constitute overlooked models for different porphyrias. The Harderian gland of rodents, where large amounts of porphyrins are synthesized, presents an underexplored potential for understanding the carcinogenic/toxic effect of porphyrin accumulation. Investigating how these animals avoid porphyrin pathogenicity may complement the use of laboratory models for porphyrias and provide new insights into the treatment of these disorders.

Human Colors-The Rainbow Garden of Pathology: What Gives Normal and Pathologic Tissues Their Color?

CONTEXT

- Colors are important to all living organisms because they are crucial for camouflage and protection, metabolism, sexual behavior, and communication. Human organs obviously have color, but the underlying biologic processes that dictate the specific colors of organs and tissues are not completely understood. A literature search on the determinants of color in human organs yielded scant information.

OBJECTIVES

- To address 2 specific questions: (1) why do human organs have color, and (2) what gives normal and pathologic tissues their distinctive colors?

DATA SOURCES

- Endogenous colors are the result of complex biochemical reactions that produce biologic pigments: red-brown cytochromes and porphyrins (blood, liver, spleen, kidneys, striated muscle), brown-black melanins (skin, appendages, brain nuclei), dark-brown lipochromes (aging organs), and colors that result from tissue structure (tendons, aponeurosis, muscles). Yellow-orange carotenes that deposit in lipid-rich tissues are only produced by plants and are acquired from the diet. However, there is lack of information about the cause of color in other organs, such as the gray and white matter, neuroendocrine organs, and white tissues (epithelia, soft tissues). Neoplastic tissues usually retain the color of their nonneoplastic counterpart.

CONCLUSIONS

- Most available information on the function of pigments comes from studies in plants, microorganisms, cephalopods, and vertebrates, not humans. Biologic pigments have antioxidant and cytoprotective properties and should be considered as potential future therapies for disease and cancer. We discuss the bioproducts that may be responsible for organ coloration and invite pathologists and pathology residents to look at a "routine grossing day" with a different perspective.

Advances in understanding the pathogenesis of congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) is a rare genetic disease resulting from the remarkable deficient activity of uroporphyrinogen III synthase, the fourth enzyme of the haem biosynthetic pathway. This enzyme defect results in overproduction of the non-physiological and pathogenic porphyrin isomers, uroporphyrin I and coproporphyrin I. The predominant clinical characteristics of CEP include bullous cutaneous photosensitivity to visible light from early infancy, progressive photomutilation and chronic haemolytic anaemia. The severity of clinical manifestations is markedly heterogeneous among patients; and interdependence between disease severity and porphyrin amount in the tissues has been pointed out. A more pronounced endogenous production of porphyrins concomitant to activation of ALAS2, the first and rate-limiting of the haem synthesis enzymes in erythroid cells, has also been reported. CEP is inherited as autosomal recessive or X-linked trait due to mutations in UROS or GATA1 genes; however an involvement of other causative or modifier genes cannot be ruled out.

Foci of altered hepatocytes in a fox squirrel (Sciurus niger) with haemochromatosis

Numerous minute milky white foci were distributed throughout the dark brown liver in an adult male fox squirrel. Histologically, the hepatic focal lesions were composed of large eosinophilic granular hepatocytes, which were mostly positive for glutathione S-transferase mu antigen and proliferating cell nuclear antigen. Electron microscopy demonstrated an increased number of mitochondria. These features corresponded to those in the eosinophilic type of foci of altered hepatocytes. Berlin blue stain showed severe haemosiderin deposition in hepatocytes, except in the focal lesions. Since the fox squirrel is known to be liable to develop congenital porphyria, it is suggested that the hepatic anomalies described may be closely associated with the development of porphyria.

Uroporphyrinogen-III synthase: molecular cloning, nucleotide sequence, expression of a mouse full-length cDNA, and its localization on mouse chromosome 7

Uroporphyrinogen-III synthase (URO-S; EC 4.2.1.75), the fourth enzyme in the heme biosynthetic pathway, is responsible for the conversion of hydroxymethylbilane to the cyclic tetrapyrrole, uroporphyrinogen III. The deficient activity of URO-S is the enzymatic defect in congenital erythropoietic porphyria (CEP), an autosomal recessive disorder. For the generation of a mouse model of CEP, the human URO-S cDNA was used to screen 2 x 10(6) recombinants from a mouse adult liver cDNA library. Ten positive clones were isolated, and dideoxy sequencing of the entire 1.6-kb insert of clone pmUROS-1 revealed 5' and 3' untranslated sequences of 144 and 623 bp, respectively, and an open reading frame of 798 bp encoding a 265-amino-acid polypeptide with a predicted molecular mass of 28,501 Da. The mouse and human coding sequences had 80.5 and 77.8% nucleotide and amino acid identity, respectively. The authenticity of the mouse cDNA was established by expression of the active monomeric enzyme in Escherichia coli. In addition, the analysis of two multilocus genetic crosses localized the mouse gene on chromosome 7, consistent with the mapping of the human gene to a position of conserved synteny on chromosome 10. The isolation, expression, and chromosomal mapping of this full-length cDNA should facilitate studies of the structure and organization of the mouse genomic sequence and the development of a mouse model of CEP for characterization of the disease pathogenesis and evaluation of gene therapy.

Animal models of inherited hematologic disease

Inherited or acquired hematologic disease is the most prevalent of all human disease when we include the hematologic disorders which are secondary to disease of other systems. It follows that the study of the fundamental mechanisms of the disease processes affecting the hematopoietic system is of prime importance and much remains to be done when one considers that in only 25% of ail hemolytic anemias is the fundamental cause eventually discovered [150]. In the current climate of societal pressures on experimental animal research, animals with spontaneous inherited disease mimicking diseases of the various physiological systems assume proportionately greater importance. These animal models have been extremely valuable in the study of fundamental questions of molecular genetics, metabolic aberrations of the cell and its membrane, synthetic mechanisms of the cell as well as clinical questions of disease manifestations, pathogenetic mechanisms and management. Exploration of differences between normal animal species offer a secondary avenue of investigation into these same fundamental questions. New animal models are being uncovered constantly and this augurs well for the future of biomedical research and the ultimate benefit to humankind and to animals in their own right.

Bovine protoporphyria: the first nonhuman model of this hereditary photosensitizing disease

Protoporphyria, a photosensitizing disease documented only in humans, was transmitted as a recessive trait to seven female calves. Cutaneous lesions were extensive, and erythrocyte and fecal protoporphyrin concentrations exceeded by far those of human protoporphyria. Average ferrochelatase activity was decreased to one-half of normal in the liver of carriers, and to about one-tenth of normal in liver, kidney, heart, spleen, lung, and marrow of protoporphyrics.

The effect of selection for body-weight on the skeletal variation of the mouse

The incidence of many minor skeletal variants in the inbred mouse strain C57BL can be influenced by the diet on which the parents live: in many cases, the effect is mediated by a correlation with body size. This also seems to be true in Falconer's (1973) Q-strain in which body size has been increased or decreased by selection. However, there was so much heterogeneity between replicates within selection lines that variants influenced by body size could be detected as a group, but not identified individually.

The activities of uroporphyrinogen synthetase and cosynthetase in congenital erythropoietic porphyria (CEP)

Normal or increased amounts of series III porphyrins with greater amounts of series I were observed on incubation of PBG in hemolysates of congenital erythropoietic porphyria vs. normal erythrocytes, human or bovine. Correlation with reticulocyte percentage was poor, in the aggregate a general trend toward increased values of both isomers I and III was noted with increasing reticulocytes. When the percent of type III was low the net amount was increased as compared with normal. Hemolysates of non-porphyric, reticulocyte-rich red cells (hemolytic or posthemorrhagic anemia) formed only minute amounts of type I porphyrin but at the same time no more, or even less type III than the porphyric hemolysates, although representing red cells of greater reticulocyte content. No evidence of deficient heme synthesis was observed in porphyric hemolysates incubayed with [14C]-porphobilinogen or 59Fe. Other studies of porphyric hemolysates incubated with and without added mouse spleen synthetase failed to reveal evidence of an absolute UPG-III cosynthetase (Co-S) deficiency. The large increases of type I porphyrin with normal or increased formation of type III, both in the disease and in the hemolysates, are believed due to a primary increase of ALA-S or UPG-S activity rather than a decrease of Co-S. Possible mutations which might be responsible for this increase are considered.