Conservation of globin genes in the "living fossil" Latimeria chalumnae and reconstruction of the evolution of the vertebrate globin family.

The (hemo-)globins are among the best-investigated proteins in biomedical sciences. These small heme-proteins play an important role in oxygen supply, but may also have other functions. In addition to well known hemoglobin and myoglobin, six other vertebrate globin types have been identified in recent years: neuroglobin, cytoglobin, globin E, globin X, globin Y, and androglobin. Analyses of the genome of the "living fossil" Latimeria chalumnae show that the coelacanth is the only known vertebrate that includes all eight globin types. Thus, Latimeria can also be considered as a "globin fossil". Analyses of gene synteny and phylogenetic reconstructions allow us to trace the evolution and the functional changes of the vertebrate globin family. Neuroglobin and globin X diverged from the other globin types before the separation of Protostomia and Deuterostomia. The cytoglobins, which are unlikely to be involved in O2 supply, form the earliest globin branch within the jawed vertebrates (Gnathostomata), but do not group with the agnathan hemoglobins, as it has been proposed before. There is strong evidence from phylogenetic reconstructions and gene synteny that the eye-specific globin E and muscle-specific myoglobin constitute a common clade, suggesting a similar role in intracellular O2 supply. Latimeria possesses two α- and two ß-hemoglobin chains, of which one α-chain emerged prior to the divergence of Actinopterygii and Sarcopterygii, but has been retained only in the coelacanth. Notably, the embryonic hemoglobin α-chains of Gnathostomata derive from a common ancestor, while the embryonic ß-chains - with the exception of a more complex pattern in the coelacanth and amphibians - display a clade-specific evolution. Globin Y is associated with the hemoglobin gene cluster, but its phylogenetic position is not resolved. Our data show an early divergence of distinct globin types in the vertebrate evolution before the emergence of tetrapods. The subsequent loss of globins in certain taxa may be associated with changes in the oxygen-dependent metabolism. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.

Bacterial and archaeal globins - a revised perspective.

A bioinformatics survey of putative globins in over 2200 bacterial and some 140 archaeal genomes revealed that over half the bacterial and approximately one fifth of archaeal genomes contain genes encoding globins that were classified into three families: the M (myoglobin-like), and S (sensor) families all exhibiting the canonical 3/3 myoglobin fold, and the T family (truncated myoglobin fold). Although the M family comprises 2 subfamilies, flavohemoglobins (FHbs) and single domain globins (SDgbs), the S family encompasses chimeric globin-coupled sensors (GCSs), single domain Pgbs (protoglobins) and SSDgbs (sensor single domain globins). The T family comprises three classes TrHb1s, TrHb2s and TrHb3s, characterized by the abbreviated 2/2 myoglobin fold. The Archaea contain only Pgbs, GCSs and TrHb1s. The smallest globin-bearing genomes are the streamlined genomes (~1.3Mbp) of the SAR11 clade of alphaproteobacteria and the slightly larger (ca. 1.7Mbp) genomes of Aquificae. The smallest genome with members of all three families is the 2.3Mbp genome of the extremophile Methylacidiphilum infernorum (Verrumicrobia). Of the 147 possible combinations of the eight globin subfamilies, only 83 are observed. Although binary combinations are infrequent and ternary combinations are rare, the FHb+TrHb2 combination is the most commonly observed. Of the possible functions of bacterial globins we discuss the two principal ones - nitric oxide detoxification via the NO dioxygenase or denitrosylase activities and the sensing of oxygen concentration in the environmental niche. In only few cases has a physiological role been demonstrated in vivo. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.

Sex chromosome DSD individuals with mosaic 45,X0 and aberrant Y chromosomes in 46,XY cells: distinct gender phenotypes and germ cell tumour risks§.

"Differences of Sexual Development (DSD)," individuals with rearranged Y chromosome breaks in their 46,XY cells are reported with male and female gender phenotypes and differences in germ cell tumour (GCT) risk. This raised the question of whether male or female gender and GCT risk depends on the site of the break and/or rearrangement of the individual´s Y chromosome. In this paper, we report molecular mapping of the breakpoint on the aberrant Y chromosome of 22 DSD individuals with a 45,X/46,XY karyotype reared with a different gender. Their Y chromosome breaks are found at different sites on the long and short Y arms. Our data indicate that gender rearing is, neither dependent on the site of Y breakage, nor on the amount of 45,X0 cells in the individuals' leukocytes. Most prominent are secondary rearrangements of the Y chromosome breaks forming di-centric Y-structures ("dic-Y"). Duplications of the short Y arm and the proximal part of the long Y arm are the results. A putative GCT risk has been analysed with immunohistochemical experiments on some dysgenetic gonadal tissue sections. With specific antibodies for OCT3/4 expression, we marked the pluripotent germ cell fraction being potential tumour precursor cells. With specific antibodies for DDX3Y, TSPY, and UTY we analyzed their putative Gonadoblastoma Y (GBY) tumour susceptibility function in the same specimen. We conclude GBY expression is only diagnostic for GCT development in the aberrant germ cells of these DSD individuals when strong OCT3/4 expression has marked their pluripotency.

AZFa candidate gene UTY and its X homologue UTX are expressed in human germ cells.

The Ubiquitous Transcribed Y (UTY a.k.a. KDM6C) AZFa candidate gene on the human Y chromosome and its paralog on the X chromosome, UTX (a.k.a. KDM6A), encode a histone lysine demethylase removing chromatin H3K27 methylation marks at genes transcriptional start sites for activation. Both proteins harbour the conserved Jumonji C (JmjC) domain, functional in chromatin metabolism, and an extended N-terminal tetratricopeptide repeat (TPR) block involved in specific protein interactions. Specific antisera for human UTY and UTX proteins were developed to distinguish the expression of both proteins in human germ cells by immunohistochemical experiments on appropriate tissue sections. In the male germ line, UTY was expressed in the fraction of A spermatogonia located at the basal membrane, probably including spermatogonia stem cells. UTX expression was more spread in all spermatogonia and in early spermatids. In female germ line, UTX expression was found in the primordial germ cells of the ovary. UTY was also expressed during fetal male germ cell development, whereas UTX expression was visible only at distinct gestation weeks. Based on these results and the conserved neighboured location of UTY and DDX3Y in Yq11 found in mammals of distinct lineages, we conclude that UTY, such as DDX3Y, is part of the Azoospermia factor a (AZFa) locus functioning in human spermatogonia to support the balance of their proliferation-differentiation rate before meiosis. Comparable UTY and DDX3Y expression was also found in gonadoblastoma and dysgerminoma cells found in germ cell nests of the dysgenetic gonads of individuals with disorders of sexual development and a Y chromosome in karyotype (DSD-XY). This confirms that AZFa overlaps with GBY, the Gonadoblastoma susceptibility Y locus, and includes the UTY gene. LAY SUMMARY: AZFa Y genes are involved in human male germ cells development and support gonadoblastoma (germ cell tumour precursor cells) in the aberrant germ cells of the gonads of females with genetic disorders of sexual development. The AZFa UTY gene on the male Y chromosome is equivalent to UTX on the female X chromosome. These genes are involved in removing gene regulators to enable activation of other genes (i.e. removal of histone methylation known as epigenetic modifications). We wanted to learn the function of UTY and UTX in developing sperm and eggs in human tissues and developed specific antibodies to detect both proteins made by these genes. Both UTY and UTX proteins were detected in adult and fetal sperm precursor cells (spermatogonia). UTX was detected in egg precursor cells (primordial germ cells). UTY was detected in gonadoblastoma and dysgerminoma tumour cells (germ cell tumours originating from genetic disorders of sexual development due to having a Y chromosome). Based on our study, we conclude that UTY is not only part of AZFa, but also of GBY the overlapping gonadoblastoma susceptibility Y region.

Prophylactic Bilateral Gonadectomy for Ovotesticular Disorder of Sex Development in a Patient With Mosaic 45,X/46,X,idic(Y)q11.222 Karyotype.

Ovotesticular disorder of sex development is historically thought to confer a relatively low risk of germ cell malignancy relative to other disorders of sex development. This is likely due in part to the high prevalence of a normal 46,XX karyotype in these patients. However, disorders of sex development represent a broad phenotypic spectrum, and often patients cannot be neatly categorized with a single diagnosis. We report an atypical case of ovotesticular disorder of sex development in a child with ambiguous genitalia and 45,X/46,XY mosaic karyotype. Prophylactic bilateral gonadectomy was performed at age 14 months.