Functional evolution of Hox proteins in arthropods

Association of TGIFLX/Y mRNA expression with azoospermia in infertile men

HOX genes are well-known to encode transcriptional regulatory proteins that play essential roles in directing embryonic development. TGIFLX/Y contains two genes, TGIFLX (X-linked) and TGIFLY (Y-linked), which are specifically expressed in human adult testes. The function(s) of these genes in normal and abnormal development are unknown. To investigate the potential role(s) of the TGIFLX/Y gene in infertile males, a nested reverse transcriptase polymerase chain reaction (RT-PCR) was performed on testicular samples from 110 patients with nonobstructive azoospermia. Although the only 51 (46.4%) of the 110 patients had detectable levels of TGIFLY expression, none of the patients with various spermatogenesis defects showed any of the TGIFLX gene expression found in normal testes. These results suggest that the function of TGIFLX may be required for the regulation of spermatogonial stem cell specification and proliferation. While functional similarity has been demonstrated among some homeobox genes, these results may refute the suggestion of redundancy between TGIFLX and TGIFLY. Furthermore, TGIFLX might be a potential biomarker candidate for male infertility assessment.

Insights into the urbilaterian brain: conserved genetic patterning mechanisms in insect and vertebrate brain development

Recent molecular genetic analyses of Drosophila melanogaster and mouse central nervous system (CNS) development revealed strikingly similar genetic patterning mechanisms in the formation of the insect and vertebrate brain. Thus, in both insects and vertebrates, the correct regionalization and neuronal identity of the anterior brain anlage is controlled by the cephalic gap genes otd/Otx and ems/Emx, whereas members of the Hox genes are involved in patterning of the posterior brain. A third intermediate domain on the anteroposterior axis of the vertebrate and insect brain is characterized by the expression of the Pax2/5/8 orthologues, suggesting that the tripartite ground plans of the protostome and deuterostome brains share a common evolutionary origin. Furthermore, cross-phylum rescue experiments demonstrate that insect and mammalian members of the otd/Otx and ems/Emx gene families can functionally replace each other in embryonic brain patterning. Homologous genes involved in dorsoventral regionalization of the CNS in vertebrates and insects show remarkably similar patterning and orientation with respect to the neurogenic region (ventral in insects and dorsal in vertebrates). This supports the notion that a dorsoventral body axis inversion occurred after the separation of protostome and deuterostome lineages in evolution. Taken together, these findings demonstrate conserved genetic patterning mechanisms in insect and vertebrate brain development and suggest a monophyletic origin of the brain in protostome and deuterostome bilaterians.

Convergent evolution of strigiform and caprimulgiform dark-activity is supported by phylogenetic analysis using the arylalkylamine N-acetyltransferase (Aanat) gene

Alternative hypotheses propose the sister order of owls (Strigiformes) to be either day-active raptors (Falconiformes) or dark-active nightjars and allies (Caprimulgiformes). In an effort to identify molecular characters distinguishing between these hypotheses we examined a gene, arylalkylamine N-acetyltransferase (Aanat), potentially associated with the evolution of avian dark-activity. Partial Aanat coding sequences, and two introns, were obtained from the genomic DNA of 16 species: Strigiformes (four species), Falconiformes (four species), Caprimulgiformes (five species), with outgroups: Ciconiiformes (one species), Passeriformes (one species), and Apterygiformes (one species). Phylogenetic trees derived from aligned, evolutionarily conserved Aanat regions did not consistently recover clades corresponding to orders Strigiformes and Falconiformes but did place a caprimulgiform clade more distant from the strigiform and falconiform species than the latter two groups are to each other. This finding was supported by spectral analysis. The taxonomic distribution of seven intronic indels is consistent with the Aanat derived phylogenetic trees and supports conventional family-level groupings within both Strigiformes and Caprimulgiformes. The phylogenetic analyses also indicate that Caprimulgiformes is a polyphyletic grouping. In conclusion the data support, but do not conclusively prove, the proposal that Falconiformes is the sister order to Strigiformes and therefore, that the dark-activity characteristic of Strigiformes and Caprimulgiformes arose by convergent evolution.

The urbilaterian brain: developmental insights into the evolutionary origin of the brain in insects and vertebrates

Classical phylogenetic, neuroanatomical and neuroembryological studies propose an independent evolutionary origin of the brains of insects and vertebrates. Contrasting with this, data from three sets of molecular and genetic analyses indicate that the developmental program of brains of insects and vertebrates might be highly conserved and suggest a monophyletic origin of the brain of protostomes and deuterostomes. First, recent results of molecular phylogeny imply that none of the currently living animals correspond to evolutionary intermediates between protostomes and deuterostomes, thus making it impossible to infer the morphological organization of an ancestral bilaterian brain from living specimens. Second, recent molecular genetic evidence provides support for the body axis inversion hypothesis, which implies that a dorsoventral inversion of the body axis occurred in protostomes versus deuterostomes, leading to the inverted location of neurogenic regions in these animal groups. Third, recent developmental genetic analyses are uncovering the existence of structurally and functionally homologous genes that have comparable and interchangeable functions in early brain development in insect and vertebrate model systems. Thus, development of the anteriormost part of the embryonic brain in both insects and vertebrates depends upon the otd/Otx and ems/Emx genes; development of the posterior part of the embryonic brain in both insects and vertebrates involves homologous control genes of the Hox cluster. These findings, which demonstrate the conserved expression and function of key patterning genes involved in embryonic brain development in insects and vertebrates support the hypothesis that the brains of protostomes and deuterostomes are of monophyletic, urbilaterian origin.

Requirement for two nearly identical TGIF-related homeobox genes in Drosophila spermatogenesis

The genetic analysis of spermatogenesis in Drosophila melanogaster has led to the identification of several genes that control the onset of meiosis, spermatid differentiation, or both. We described two tightly linked and nearly identical homeobox genes of the TGIF (TG-interacting factor) subclass called vismay and achintya that are essential for spermatogenesis in Drosophila. In flies deficient for both genes, spermatogenesis is blocked prior to any spermatid differentiation and before the first meiotic division. This suggests that vismay and achintya function at the same step as two previously characterized meiotic arrest genes, always early and cookie monster. Consistent with this idea, both always early and cookie monster are still expressed in flies deficient in vismay and achintya. Conversely, Vismay and Achintya proteins are present in always early mutant testes. Co-immunoprecipitation experiments further suggest that Vismay and Achintya proteins exist in a complex with Always early and Cookie monster proteins. Because Vismay and Achintya are likely to be sequence-specific DNA binding factors, these results suggest that they help to specify the spermatogenesis program by recruiting or stabilizing Always early and Cookie monster to specific target genes that need to be transcriptionally regulated during testes development.