Temperature-dependent sex determination: upregulation of SOX9 expression after commitment to male development.
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In mammals, birds and reptiles the morphological development of the gonads appear to be conserved. This conservation is evident despite the different sex determining switches employed by these vertebrate groups. Mammals exhibit chromosomal sex determination (CSD) where the key sex determining switch is the Y-linked gene, SRY. Although SRY is the trigger for testis determination in mammals, it is not conserved in other vertebrate groups. However, a gene closely related to SRY, the highly conserved transcription factor, SOX9, plays an important role in the testis pathway of mammals and birds. In contrast to the CSD mechanism evident in mammals and birds, many reptiles exhibit temperature dependent sex determination (TSD) where the egg incubation temperature triggers sex determination. Here we examine the expression of SOX9 during gonadogenesis in the American alligator, (Alligator mississippiensis), a reptile that exhibits TSD. Alligator SOX9 is expressed in the embryonic testis but not in the ovary. However, the timing of SOX9 upregulation in the developing testis is not consistent with a role for this gene in the early stages of alligator sex determination. Since SOX9 upregulation in male embryos coincides with the structural organisation of the testis, SOX9 may operate farther downstream in the vertebrate sex differentiation pathway than previously postulated. (+info)
The existence of Merkel cells in the lingual connective tissue of the Surinam caiman, Caiman crocodilus crocodilus (order Crocodilia).
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The tongue of the Surinam caiman (a reptilian species) was studied by light microscopy including immunohistochemistry for protein gene product 9.5 (PGP 9.5), and transmission electron microscopy. The connective tissue immediately under taste buds housed a cluster of cells immunoreactive for PGP 9.5. These cells synapsed on nerves, and their cytoplasm contained characteristic granules of 90 nm in the mean diameter, glycogen particles, and bundles of intermediate filaments. In light of these ultrastructural features, they were identified as Merkel cells. The Merkel cells were also surrounded by Schwann cells. These findings indicate that the present Merkel cell-neurite-Schwann cell complex is comparable to the avian Merkel corpuscle. On the basis of the granule localization in the cytoplasm, the caiman Merkel cell was presumed to be involved in not only mechanoreception but also endocrine or paracrine functions. (+info)
Origin of gene overlap: the case of TCP1 and ACAT2.
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The human acetyl-CoA acetyltransferase 2 gene, ACAT2, codes for a thiolase, an enzyme involved in lipid metabolism. The human T-complex protein 1 gene, TCP1, encodes a molecular chaperone of the chaperonin family. The two genes overlap by their 3'-untranslated regions, their coding sequences being located on opposite DNA strands in a tail-to-tail orientation. To find out how the overlap might have arisen in evolution, the homologous genes of the zebrafish, the African toad, caiman, platypus, opossum, and wallaby were identified. In each species, standard or long polymerase chain reactions were used to determine whether the ACAT2 and TCP1 homologs are closely linked and, if so, whether they overlap. The results reveal that the overlap apparently arose during the transition from therapsid reptiles to mammals and has been retained for >200 million years. Part of the overlapping untranslated region shows remarkable sequence conservation. The overlap presumably arose during the chromosomal rearrangement that brought the two unrelated and previously separated genes together. One or both of the transposed genes found by chance signals that are necessary for the processing of their transcripts to be present on the noncoding strand of the partner gene. (+info)
Identification and characterization of proteins synthesized de novo and secreted by the reproductive tract of the American alligator, Alligator mississippiensis.
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The objectives of this study were to identify, characterize and examine differences in proteins synthesized de novo and secreted by different regions of the reproductive tract of the American alligator, Alligator mississippiensis, during three reproductive (vitellogenic, gravid, post-clutch) and one non-reproductive state. After capture, alligators from lakes in north central Florida were anaesthetized, the reproductive tract excised aseptically, the size of any follicle determined, and different functional regions of the tract dissected out and partitioned for explant culture. Analysis of the biosynthetic activity indicated regional variations within the tract, differences among reproductive groups and region by status interactions. When oviductal regions were considered regardless of reproductive status, the greatest incorporation of [3H]Leu into secreted nondialysable macromolecules was by the anterior and posterior infundibulum and oviductal tube compared with the transition zone and the uterus. When status was included, the biosynthetic activity of the anterior and posterior portion of the tract in non-reproductive alligators was not different, whereas that of the posterior region of the reproductive group (vitellogenic, gravid, post-clutch) was significantly lower than that of the anterior region. This finding indicates that regulation of protein synthesis and secretion by the non-reproductive alligator tract is different from that in the tract of the reproductive group. Explant-conditioned media were analysed by one-dimensional and two-dimensional SDS-PAGE and fluorography. Sixteen major proteins in culture media were identified as de novo synthesized, by relative molecular weight, by isoelectric point and by differences in distribution determined for reproductive status and oviductal region. Six proteins were examined by N-terminal amino acid microsequence analysis. On the basis of a 29 amino acid sequence, the major oviductal protein, alligator protein 1 (aP1: M(r) 55,000, basic), found in the infundibulum and tube of vitellogenic alligators, was identical to the major protein isolated from alligator egg albumen. Four proteins (aP4-aP7) were sequenced and shown to be significantly related to immunoglobulin heavy chains from several species. This study demonstrated that a large number of proteins are synthesized de novo and released by the female alligator reproductive tract and that there are biosynthetic activity differences by reproductive status and region. Six proteins have been identified, several of which may be incorporated into alligator egg albumen and some of which appear to be different from proteins found in the egg albumens of other species. (+info)
What determines the bending strength of compact bone?
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The bending strength of a wide variety of bony types is shown to be nearly linearly proportional to Young's modulus of elasticity/100. A somewhat closer and more satisfactory fit is obtained if account is taken of the variation of yield strain with Young's modulus. This finding strongly suggests that bending strength is determined by the yield strain. The yield stress in tension, which might be expected to predict the bending strength, underestimates the true bending strength by approximately 40 %. This may be explained by two phenomena. (1) The post-yield deformation of the bone material allows a greater bending moment to be exerted after the yield point has been reached, thereby increasing the strength as calculated from beam formulae. (2) Loading in bending results in a much smaller proportion of the volume of the specimens being raised to high stresses than is the case in tension, and this reduces the likelihood of a weak part of the specimen being loaded to failure. (+info)
Evolution of the ventricles.
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We studied the evolution of ventricles by macroscopic examination of the hearts of marine cartilaginous and bony fish, and by angiocardiography and gross examination of the hearts of air-breathing freshwater fish, frogs, turtles, snakes, and crocodiles. A right-sided, thin-walled ventricular lumen is seen in the fish, frog, turtle, and snake. In fish, there is external symmetry of the ventricle, internal asymmetry, and a thick-walled left ventricle with a small inlet chamber. In animals such as frogs, turtles, and snakes, the left ventricle exists as a small-cavitied contractile sponge. The high pressure generated by this spongy left ventricle, the direction of the jet, the ventriculoarterial orientation, and the bulbar spiral valve in the frog help to separate the systemic and pulmonary circulations. In the crocodile, the right aorta is connected to the left ventricle, and there is a complete interventricular septum and an improved left ventricular lumen when compared with turtles and snakes. The heart is housed in a rigid pericardial cavity in the shark, possibly to protect it from changing underwater pressure. The pericardial cavity in various species permits movements of the heart-which vary depending on the ventriculoarterial orientation and need for the ventricle to generate torque or spin on the ejected blood- that favor run-off into the appropriate arteries and their branches. In the lower species, it is not clear whether the spongy myocardium contributes to myocardial oxygenation. In human beings, spongy myocardium constitutes a rare form of congenital heart disease. (+info)
Reptilian chemistry: characterization of dianeackerone, a secretory product from a crocodile.
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The major volatile component in the paracloacal glandular secretion of the adult African dwarf crocodile (Osteolaemus tetraspis) was isolated and characterized as a 19-carbon aromatic ketone, dianeackerone (3,7-diethyl-9-phenyl-2-nonanone). This ketone is absent from the secretion of immatures. Careful examination of dianeackerone samples isolated from individual adults revealed that this ketone occurs as both the (3S, 7S) and (3S, 7R) stereoisomers, with different individuals presenting strikingly different ratios of the isomeric forms. Our initial suspicion that the stereoisomeric dianeackerones might be indicators of gender proved untenable, leaving the role of these glandular constituents a challenge for future study. (+info)
Reptilian chemistry: characterization of a family of dianeackerone-related steroidal esters from a crocodile secretion.
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The African dwarf crocodile, Osteolaemus tetraspis (Crocodilidae, Reptilia), possesses a pair of skin glands, the paracloacal glands, the secretion of which is thought to be used to mark nest sites or attract mates. Ten aromatic steroidal esters were isolated from this secretion and characterized on the basis of NMR spectroscopic investigations, electrospray ionization-MS analyses, and chemical degradation. These esters, which account for more than 90% of the paracloacal glandular secretion, are derived from either cholesterol or cholestanol, esterified with a C-20 or C-22 acid closely related to dianeackerone, the only significant volatile compound found in this secretion. (+info)