The Bicuspid Condition of the Aortic Valve Does Not Alter the Incidence of Accessory Coronary Artery Ostia in Syrian Hamsters (Mesocricetus auratus).

In man and Syrian hamsters (Mesocricetus auratus), the prevalence of anomalies in the origin of the coronary arteries is significantly higher in individuals with bicuspid than with normal aortic valves. In hamsters, the incidence of accessory ostia is similar in individuals with normal and anomalous coronary arteries, all of them possessing a normal (tricuspid) aortic valve. In order to evaluate whether or not the presence of bicuspid aortic valves alters the incidence of accessory ostia, 1,050 hearts from hamsters with bicuspid valves were examined. In 594 of them the coronary arteries were normal. The remaining 456 hearts showed coronary artery anomalies characterized by the absence of any artery arising from the left side of the valve. The incidence of accessory ostia was 3.9% in hamsters with normal coronary arteries and 2.2% in those with anomalous coronary patterns. Overall, 3.1% of the accessory ostia were associated with a septal artery and another 0.2% with a conal artery. These data referring to the bicuspid valves were compared with those already published on normal valves. The results of statistical analyses showed that having a bicuspid aortic valve does not alter the incidence of accessory coronary ostia. In the set of tricuspid and bicuspid valves, the incidence of accessory ostia was significantly lower on the left side than on the right side of the valve. This, together with the fact that in the present animal model the coronary anomalies were characterized by the absence of arteries on the left side of the valve, suggests that the embryonic region corresponding to the left side of the aortic valve primordium is particularly associated with preventing the normal development of coronary vessels.

The arrangement of the coronary artery trunks is subject to inheritance factors: A study in Syrian hamsters.

The concept that anatomical variations in the coronary artery tree might be influenced by genes is relatively old. However, empirical evidence on the effect of genotype on the coronary morphology is still scarce. In the Syrian hamster, there is a septal coronary artery which arises from the left or from the right coronary artery and supplies most of the interventricular septum. The aim was to decide whether the anatomical origin of the septal artery is subject to inheritance factors. Overall, 483 internal casts of the heart and coronary arteries were examined. All the hamsters included in this study had normal coronary arteries. The results of 74 crosses were compared statistically to seek for any significant difference between the phenotypes of the offspring and the phenotypes of the parents. The left septal artery was over-represented in the offspring of crosses between parents having both a left septal artery (p < .01), while the right septal artery was over-represented in the offspring of crosses between parents, one with a right and the other with a left septal artery (p < .001), and, more markedly, in the offspring of crosses between parents both with a right septal artery (p < .001). These results are the first to reveal that the coronary artery pattern is influenced by genetic factors, at least in its proximal portion with regard to the aorta.

Dicephalous v. diprosopus sharks: record of a two-headed embryo of Galeus atlanticus and review of the literature.

As far as is known, this paper gives the first description of a two-headed shark embryo belonging to an oviparous species, Galeus atlanticus (Carcharhiniformes: Scyliorhinidae). The specimen was detected among 797 embryos intended for cardiovascular studies, which represents a defect incidence of 0·13%. Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side. The two heads fused behind the gills. On the single body, there were four anticipated dorsal fins, two anterior, right and left and two posterior, right and left. Ventrally, the specimen possessed two pairs of pectoral fins, a pair of pelvic fins and one anal fin. Two adjacent notochords, two neural tubes and two dorsal aortas ran along the body, which bent 180° at its posterior portion. There were two hearts, two oesophaguses, two stomachs, two livers, but a single intestine with a spiral valve. Previous reports of conjoined twins in sharks are scarce and only refer to oviparous and ovoviviparous species. Seven dicephalous sharks reported so far were similar to the specimen described here, namely, with two totally separated heads on one body. Instead, only one case of diprosopus shark has been reported; it had a single body and a single head with partial duplication of the face. Two further cases described in the literature as dicephalous or simply as abnormal sharks should be better regarded as diprosopus, while another three cases, also considered dicephalous, showed a mixture of characteristics of diprosopia and dicephalia.

Heart pigmentation in the gray bichir, Polypterus senegalus (Actinopterygii: Polypteriformes).

The occurrence of pigment cells in the heart is well documented in amphibians, birds and mammals. By contrast, information on heart pigmentation in fish is extremely sparse. The aim is to report the presence of pigment cells over the entire surface of the heart in the gray bichir, Polypterus senegalus. The sample consisted of 12 hearts, which, after gross anatomical examination, were studied using histochemical and immunohistochemical techniques for light microscopy, and transmission electron microscopy. The pigment cells were located in the subepicardium, showing a regular distribution pattern across the whole heart, except for the anterior end of the outflow tract, where the pigmentation was much more intense. The cells contained dark, ovoid-shaped organelles which was consistent with a melanosome cell identity. As in other vertebrates, the physiological role of the pigment cells in the heart of the gray bichir is unknown. The absence of such cells in hearts of other polypteriforms suggests that cells containing melanin are not essential for normal fish heart function. Basing on literature data concerning tetrapods, it can be inferred that the pigment cells of the heart of the gray bichir derive from the neural crest. If this were true, our findings would provide the first evidence for the presence of neural crest-derived cells in the subepicardium of adult hearts of early actinopterygians.

Ectopic origin of coronary arteries from the aorta in Syrian hamsters (Mesocricetus auratus).

An ectopic origin of the coronary artery from the aorta beyond the sinotubular junction, a condition commonly referred to as 'coronary artery high take-off', has been described in man and C57BL/6 mice. The present paper reports this congenital coronary artery anomaly in the Syrian hamster (Mesocricetus auratus). Hearts from 14 individuals, aged 53-350 days, were examined by means of a corrosion-cast technique, scanning electron microscopy or histological and immunohistochemical techniques. In 11 hamsters, the right coronary artery was the ectopic vessel. In the other three animals there was a solitary coronary ostium in the aorta. In all cases, the ectopic coronary artery originated at an acute angle and a valve-like ridge was in front of the coronary artery ostium. The ectopic arteries examined microscopically showed an intramural trajectory within the aortic wall. In the hearts with a solitary ostium in the aorta, the left main coronary artery coursed between the aorta and the pulmonary artery. In man, all of these anomalous conditions place the individual at risk of myocardial ischaemia and sudden death. However, none of the affected hamsters had clinical signs of disease. Intimal thickenings of increasing size with age were present in the intramural coronary artery segment of eight hamsters aged 106 days or older, examined histologically. The present findings fit with the notion that coronary arteries with acute angle take-off and an intramural course are subjected to unusual wear and tear, leading to tissue changes in the vessel wall.

Intimal thickening of coronary arteries in the rabbitfish, Chimaera monstrosa L. (Chondrichthyes: Holocephali).

This study is the first to report the occurrence of intimal thickening of coronary arteries in a holocephalan, namely the rabbitfish, Chimaera monstrosa. The sample studied consisted of five hearts from rabbitfish with body weights ranging between 12 g and 1116 g. The specimens were fixed in formalin, in methanol:acetone:water (MAW), or in paraformaldehyde and were examined by brightfield and polarization light microscopy. Coronary arteries from three larger animals displayed focal intimal thickenings, which were located in the left main coronary artery trunk, at the level of the cono-ventricular junction, and in several intramyocardial ventricular arteries. The vascular changes were characterized by myointimal proliferation, breakage or absence of the inner elastic lamina, and, in one case, by increased collagen within the myointimal proliferation. Taking into account the severity of the coronary arterial changes, their location, and the body weight of the affected animals, we conclude that (1) these changes are age-related in the rabbitfish and (2) local intense mechanical tension seems to be an important factor in their formation in this species.

Synthesis of N-alkyl-beta-D-glucosylamines and their antimicrobial activity against Fusarium proliferatum, Salmonella typhimurium, and Listeria innocua.

In this study, different N-alkyl-beta-D-glucosylamines were evaluated for both antifungal and antibacterial activity against Fusarium proliferatum (INRA, MUCL 1807.7), Listeria innocua (ISTAB, Université Bordeaux 1), and Salmonella typhimurium (Institut Pasteur 5858). The tested glucosylamines were beta-D-glucosylamine (GPA), N-ethyl-beta-D-glucosylamine (EtGPA), N-butyl-beta-D-glucosylamine (BuGPA), N-hexyl-beta-D-glucosylamine (HeGPA), N-octyl-beta-D-glucosylamine (OcGPA), N-dodecyl-beta-D-glucosylamine (DoGPA), N-(2-hydroxyethyl)-beta-D-glucosylamine (HEtGPA), N,N-di(2-hydroxyethyl)-beta-D-glucosylamine (DHEtGPA) and N,N-diethyl-beta-D-glucosylamine (DEtGPA). The effectiveness of N-alkyl length, N-substitution, and N-hydroxyalkyl groups on both antibacterial and antifungal activity were evaluated. Results indicated that these compounds exhibited different biological activities and their effectiveness was highly increased from short to long N-alkyl chains. DoGPA exhibited more potent biological activity against all target strains than other N-alkyl glucosylamines tested. Using a radial growth method, we demonstrated that this compound completely inhibited fungal growth at 0.5 x 10(-4) mol mL(-1), while OcGPA and HeGPA lead to 71% and 43% fungal inhibition, respectively. Using the coating method, we demonstrated that DoGPA completely inhibited bacterial growth at 0.025 x 10(-4) and 0.05 x 10(-4) mol mL(-1) for L. innocua and S. typhimurium, respectively, while at the same concentrations, OcGPA exhibited weaker antibacterial activity of 12% and 27%, respectively, for L. innocua and S. typhimurium. The hole plate method enabled us to estimate the minimum inhibitory concentration (MIC) of DoGPA found to be 0.02 x 10(-4) and 0.025 x 10(-4) mol mL(-1) for L. innocua and S. typhimurium, respectively. Glucosylamines with N-hydroxyalkyl and short N-alkyl chains varying from C-2 to C-4 exhibited weaker antimicrobial activity.

Rudimentary coronary artery in Syrian hamsters (Mesocricetus auratus).

Congenital underdevelopment of one or more main branches of the coronary arteries has been reported in man, but not in non-human mammals. In man, this defective coronary artery arrangement may cause myocardial ischaemia and even sudden death. The main goal of this study was to describe the coronary artery distribution patterns associated with the presence of a markedly underdeveloped (rudimentary) coronary artery in Syrian hamsters. Moreover, an attempt was made to explain the morphogenesis of these patterns, according to current knowledge on coronary artery development. Eleven affected hamsters belonging to a laboratory inbred family were examined by means of internal casts of the heart, great arterial trunks and coronary arteries. The aortic valve was tricuspid (normal) in seven hamsters and bicuspid in the other four. A rudimentary coronary artery arose from the right side of the aortic valve in four specimens, from the left side of the aortic valve in a further three, and from the dorsal aortic sinus in the remaining four. In all cases, a second, well-developed coronary artery provided for all the coronary blood flow. Except for the existence of a rudimentary coronary artery, the present anomalous coronary artery distribution patterns are similar to coronary artery patterns reported in Syrian hamsters, dogs and humans in association with a solitary coronary ostium in aorta. We suggest that an unusual prolonged time interval in the development of the embryonic coronary stems might be a key factor in the formation of coronary arteries displaying significantly dissimilar developmental degrees.

The coronary arteries of the C57BL/6 mouse strains: implications for comparison with mutant models.

There are few detailed descriptions of the coronary arterial patterns in the mouse. Some recent reports on coronary anomalies in mutant mouse models have uncovered the importance of several genes (i.e. iv and connexin43) in coronary morphogenesis. These mutations spontaneously appeared (iv) or were generated (connexin43) in a C57BL/6 background, which is widely used for the development of mutant mice. We have studied the origin and course of the main coronary arteries of two C57BL/6 mouse strains. Unusual anatomical coronary arterial patterns were found, including: solitary ostium in aorta, accessory ostium, high take-off, aortic intramural course, slit-like ostium, sinus-like ostium and origin of a septal artery from the left coronary artery. In humans, some of these conditions are clinically relevant. Most of these patterns, which differ from those observed in wild mice and Swiss albino mice, coincide with those previously found in iv/iv and connexin43 knockout mice. The results indicate that there is variability in the coronary arterial arrangement of the laboratory mouse. Care should be taken when analysing coronary phenotypes of mutant mouse models.

Number of coronary ostia in Syrian hamsters (Mesocricetus auratus) with normal and anomalous coronary arteries.

Little attention is being paid to the presence of accessory coronary artery ostia in man and non-human mammals due to their limited clinical relevance. However, information about their frequency and the cardiac territories irrigated by the vessels arising from them is of interest to obtain an accurate survey of the establishment of the coronary artery system in each species. The aim here was to compare the incidence and significance of the accessory coronary ostia in Syrian hamsters with normal coronary arteries and several coronary anomalies characterized by the absence of a left coronary artery originating from the left aortic sinus. The hearts from 2829 hamsters were examined using a corrosion-cast technique, micro-dissection, histochemical techniques, and scanning electron microscopy. Overall, 148 specimens displayed accessory ostia. A limited number of them belonged to the conal artery which supplies the wall of the right ventricular outflow tract. The other accessory ostia led to the septal artery, a vessel which irrigates the most part of the interventricular septum. The incidence of accessory ostia in normal and anomalous coronary artery patterns was quite similar. This suggests that the morphogenetic deviations producing the coronary artery anomalies reported in this study do not alter the connections of the septal and conal arteries to the aorta. The present observations lead to the notion that in the Syrian hamster, the septal artery should be regarded as a third coronary artery.

Water and moisture susceptibility of chitosan and paper-based materials: structure-property relationships.

Environmentally friendly and potentially bioactive food packaging based on chitosan-coated papers were elaborated. The morphology and the microstructure of these new materials were characterized by infrared spectroscopy and scanning electron microscopy. These observations suggested that the chitosan penetrated deeply into the paper, embedding the cellulose fibers, instead of forming a layer as expected. Through the barrier properties against moisture, the liquid water sensitivity, and NMR-relaxometry measurements, the water interactions were evaluated on the chitosan films and the chitosan-coated papers. They revealed that the coating by a chitosan film forming solution improved the paper moisture barrier properties but the surface hydrophilicity remained high. Relaxometry studies showed that, due to its hydrophilic character, chitosan controlled the interaction with water, despite the very low amount of deposit. On the other hand, the mechanical properties of papers were unmodified by the chitosan coating, which did not fundamentally affect the solid structure of the papers.

Separate origin of the main components of the left coronary artery in Syrian hamsters (Mesocricetus auratus).

This study describes a rare congenital coronary artery anomaly in the Syrian hamster; namely, the separate origin of the obtuse marginal and left circumflex arteries which are the main components of the left coronary artery. The hearts of nine affected animals were examined by means of a corrosion-cast technique and histology. The hamsters belonged to a laboratory inbred family with a high incidence of coronary artery anomalies and bicuspid aortic valve. The aortic valve was tricuspid in three hamsters and bicuspid in the other six hamsters. In all cases, the right coronary artery was normal, whereas the left coronary artery main trunk was absent. The present anomalous coronary artery patterns could be classified into two main entities: (i) ectopic origin of the obtuse marginal artery from the right aortic sinus or from the right coronary artery, with the left circumflex artery arising from the left side of the aortic valve; and (ii) ectopic origin of both the obtuse marginal artery from the right aortic sinus or from the right coronary artery and left circumflex artery from the dorsal aortic sinus. In all cases, the obtuse marginal artery coursed to the right side of the heart through the ventral wall of the right ventricular outflow tract. When the left circumflex artery arose from the dorsal aortic sinus, it formed an acute angle with the aortic wall. This report seems to be the first to describe the separate origin of the main components of the left coronary artery in a non-human mammalian species. In man, the congenital coronary artery and aortic valve defects reported herein may entail the risk of clinical complications. However, none of the affected hamsters showed signs of disease.

Anomalous origin of the left coronary artery from the right side of the aortic valve in Syrian hamsters (Mesocricetus auratus).

This study describes the coronary artery distribution patterns associated with the anomalous origin of the left coronary artery from the right side of the aortic valve in Syrian hamsters. The hearts of 15 affected animals were examined by means of a corrosion-cast technique, histology and scanning electron microscopy. The hamsters belonged to a laboratory inbred colony with a high incidence of coronary artery anomalies and bicuspid aortic valves. The aortic valve was tricuspid in eight hamsters and bicuspid in the other seven. In all cases, the right coronary artery was normal, whereas the left main coronary artery trunk arose from the right aortic sinus or from the right side of the ventral aortic sinus when the aortic valve was bicuspid. In 12 specimens, the left main trunk crossed the infundibular septum and then divided into the left circumflex branch and the obtuse marginal branch. In another specimen, the course of the left main trunk was ventral to the right ventricular outflow tract; in the remaining two, it surrounded the aorta dorsally. In man, some of these distribution patterns may cause myocardial ischaemia and sudden death. The present findings prove that the origin of the left coronary artery from the right aortic sinus occurs in primitive mammals such as the Syrian hamster, suggesting that the defect may occur in other mammalian species. Its possible occurrence should be borne in mind in domestic animals, especially in those with signs of myocardial ischaemia after strenuous activity.

Formation of cartilage in congenital bicuspid aortic valves of Syrian hamsters (mesocricetus auratus).

The formation, topographical location and calcification of cartilage in congenital bicuspid aortic valves of 235 Syrian hamsters aged 0--173 days were studied by histological, histochemical and immunohistochemical techniques. In all animals the aortic valve was bicuspid; it had two leaflets, ventral and dorsal, each supported by its own aortic sinus. In 141 valves, a more or less developed raphe was located in the ventral sinus. The remaining 94 valves were devoid of any raphe. The first sign of valvular chondrogenesis was the presence of small groups of cells embedded in a type II collagen-positive extracellular matrix. These cellular groups, which appeared as early as 2 days after birth, became converted into hyaline cartilage or fibrocartilage. A considerable proportion (67%) of the valvular cartilages developed within the first 6 weeks of life. The cartilaginous tissue was capable of forming anywhere along the attachments of the valve leaflets to their supporting sinuses. However, statistical analyses substantiated the observation that the bases of the sinuses and raphes were the valvular regions particularly prone to the development of cartilage. At these sites, the cartilage was usually hyaline and often became calcified. The findings were consistent with the assumption that intense mechanical stimulation plays an important role in the formation of the valvular cartilage. Moreover, these findings supplied new evidence that in the cardiac semilunar valves of Syrian hamsters, cartilage formation does not involve the aggregation of large numbers of cells before their differentiation into chondrocytes. The valvular hyaline cartilages appear to act as competent pivots, resisting mechanical tensions generated during the cardiac cycle. Deposition of calcium in the matrix can be regarded as a reinforcement process of the cartilaginous tissue. Finally, it is hypothesized that the formation of cartilage in the aortic valves of hamsters prevents dystrophic calcification of the valve, a pathological change that causes aortic stenosis in man, especially in patients with a bicuspid aortic valve.

Formation of cartilaginous foci in the central fibrous body of the heart in Syrian hamsters (Mesocricetus auratus).

The formation of cartilage in the mammalian heart has been studied in the aortic and pulmonary valves. The chondrogenetic process that takes place in the cardiac skeleton is still unknown. The present study was designed to illustrate the ontogeny of cartilaginous foci occurring in the central fibrous body of the Syrian hamster (Mesocricetus auratus) heart. Hearts from 472 animals aged 0-708 days were examined using histological, histochemical and immunohistochemical techniques. Cartilage was present in the central fibrous body of 118 (25%) specimens. A further 104 hamsters were used for the detection of calcific deposits in the central fibrous body. Six (5.8%) showed calcified cartilage. The first sign related to chondrogenesis was the presence of small groups of cells embedded in a type II collagen-positive extracellular matrix. These cellular groups, which can appear as early as 2 days after birth, differentiate into hyaline cartilage or, less frequently, into fibrocartilage. The highest production of cartilaginous foci takes place between days 40 and 80. Thereafter, formation of new foci is uncommon. This indicates that appearance of cartilage in the central fibrous body of the heart is not a consequence of cardiac aging. The cartilaginous foci seem to act as pivots resisting mechanical tensions generated during the cardiac cycle. Deposition of calcium in the extracellular matrix of the foci can be regarded as a reinforcement of the cartilaginous tissue.

Formation of cartilage in aortic valves of Syrian hamsters.

The formation of cartilage in aortic valves of Syrian hamsters was studied using histological, histochemical and immunohistochemical techniques. The sample consisted of 281 specimens aged 0-363 days, all of which had a normal (tricuspid) aortic valve. The first sign of valvular chondrogenesis is the presence of small groups of cells embedded in a type II collagen-positive matrix. These groups of cells, which can appear as early as one day after birth, increase in size and differentiate into hyaline cartilage or fibrocartilage. From the fourth day of life, all hamsters examined displayed cartilaginous foci in the aortic valve. They were located along the fibrous attachments of the valve leaflets to their respective sinuses, including the valve commissures. A considerable proportion (76%) of cartilages formed within the first 40 days of life, that is during the period of time in which the histogenesis of the valve takes place. The present observations are consistent with the assumption that in mammals, the precursors of the aortic valve chondrocytes are neural crest-derived cells. Results of a statistical analysis substantiate that the incidence is significantly higher in (1) the territory that comprises the collagenous condensation of the ventral commissure and the ventro-lateral and proximal fibrous attachments of the right leaflet to its sinus, and (2) the proximal fibrous attachment of dorsal leaflet to its sinus. These findings together with data in the literature concerning the distribution of stress in each leaflet-sinus assembly of the valve during the cardiac cycle, suggest that mechanical action might play an inductive role in the formation of the cartilaginous tissue in the aortic valve of mammals. In addition, they point to the possibility that locally intense mechanical stimulation is responsible for the differentiation of the anticipated cartilaginous tissue into hyaline cartilage.

The conus valves of the adult gilthead seabream (Sparus auratus).

The conus (bulbo-ventricular) valves of teleosts perform a key function in the control of blood backflow during ventricular diastole. However, the structural characteristics of these valves are almost unknown. This paper presents a systematic anatomical, histological and structural study of the conus valves of the adult gilthead seabream (Sparus auratus). S. auratus shows two major left and right valves consisting of the leaflet and the supporting sinus. Each valvar leaflet can be divided into a stout proximal body and a flap-like distal region. The proximal body is structured into three layers: a luminal fibrosa, a dense cellular core and a parietal fibrosa. The luminal fibrosa is a collagenous structure extending the entire length of the leaflet, while the parietal fibrosa is restricted to the most proximal area. The dense cellular core consists of fibroblastic cells and a matrix rich in glycoconjugates, collagen and elastin. The histochemical and structural data suggest that the luminal fibrosa bears most of the force associated with valvar closure, while the cellular core acts as a cushion dampening vibrations and absorbing the elastic recoil. The sinus wall is a fibrous layer which shows proximal-distal differences in thickness. It also shows compositional differences that can be related to mechanical function. We describe the presence of a fibrous cylinder formed by the sinus wall, the fibrous interleaflet triangles and the fibrous layer that covers the inner surface of the conus myocardium. This fibrous cylinder constitutes the structural nexus between the ventricle, the conus and the bulbus arteriosus, provides support for the conus valves and separates the valvar complex from the surrounding tissues. The structure of the conus valves in S. auratus is different from that found in other vertebrates. Anatomical similarities between the conus valves and the mammalian arterial valves are emphasized. Each phyletic group appears to have developed specific structures in order to perform similar functions.

The conus arteriosus of the adult gilthead seabream (Sparus auratus).

This paper reports on the presence of the conus arteriosus in the heart of the adult gilthead seabream, Sparus auratus (Perciformes, Teleostei). The junctional region between the single ventricle and the bulbus arteriosus has been studied by conventional light microscopy, and by scanning and transmission electron microscopy. In addition, fluorescent phalloidin and antibodies against the muscle myosin heavy chains, laminin and collagen type IV have been used. The conus arteriosus is a distinct muscular segment interposed between the ventricle and the bulbus arteriosus. It is clearly different from the bulbus arteriosus due to its myocardial nature. It can also be distinguished from the ventricular myocardium because: (1) it has a conus shape; (2) it is formed by compact, well-vascularized myocardium; (3) it is surrounded on its inner and outer faces by fibrous layers rich in collagen and elastin; (4) it constitutes the anatomical support of the so-termed conus valves; (5) it shows intense staining for laminin and type-IV collagen; and (6) the myocardial cells located close to the inner fibrous layer are helicoidally arranged. By contrast, the ventricular myocardium is highly trabecular, lacks a compacta, shows no vessels, and presents barely detectable amounts of laminin and collagen type IV. The presence of a distinct conus arteriosus in the heart of an evolutionary advanced teleost species indicates that the conus is not a vestigial segment from the evolutionary or embryological points of view. The characteristic spatial arrangement of the conus myocytes strongly suggests that the conus is implicated in the mechanical performance of the conus valves.

Species-specific differences of myosin content in the developing cardiac chambers of fish, birds, and mammals.

Key morphogenetic events during heart ontogenesis are similar in different vertebrate species. We report that in primitive vertebrates, i.e., cartilaginous fishes, both the embryonic and the adult heart show a segmental subdivision similar to that of the embryonic mammalian heart. Early morphogenetic events during cardiac development in the dogfish are long-lasting, providing a suitable model to study changes in pattern of gene expression during these stages. We performed a comparative study among dogfish, chicken, rat, and mouse to assess whether species-specific qualitative and/or quantitative differences in myosin heavy chain (MyHC) distribution arise during development, indicative of functional differences between species. MyHC RNA content was investigated by means of in situ hybridisation using an MyHC probe specific for a highly conserved domain, and MyHC protein content was assessed by immunohistochemistry. MyHC transcripts were found to be homogeneously distributed in the myocardium of the tubular and embryonic heart of dogfish and rodents. A difference between atrial and ventricular MyHC content (mRNA and protein) was observed in the adult stage. Interestingly, differences in the MyHC content were observed at the tubular heart stage in chicken. These differences in MyHC content illustrate the distinct developmental profiles of avian and mammalian species, which might be ascribed to distinct functional requirements of the myocardial segments during ontogenesis. The atrial myocardium showed the highest MyHC content in the adult heart of all species analysed (dogfish (S. canicula), mouse (M. musculus), rat (R. norvegicus), and chicken (G. gallus)). These observations indicate that in the adult heart of vertebrates the atrial myocardium contains more myosin than the ventricular myocardium.