Segmentation is a fundamental feature of vertebrate body plans, and variation in vertebral number contributes substantially to morphological diversity. Although sexual dimorphism in vertebral number has been documented in several vertebrate lineages, its developmental basis remains poorly understood. Here, we report pronounced sexual dimorphism in vertebral number in the western Indian endemic ricefish Oryzias setnai, distributed across ~1800 km. Radiographic analyses of individuals collected throughout its range revealed that vertebral number increased with latitude in both sexes, while males consistently possessed more vertebrae than females irrespective of geographic origin. Size-adjusted analyses showed that this dimorphism is associated with sex differences in head size and position-dependent variation in vertebral length. However, positional allometric analyses demonstrated that both the magnitude and direction of these sex differences vary markedly during growth. In particular, among smaller individuals, posterior vertebrae were relatively shorter in males than in females, suggesting reduced somite length in the posterior body axis of male embryos and potentially reflecting sex-specific differences in the dynamics of somitogenesis. Given that this variation arises between males and females within a single species sharing an essentially identical genetic background, O. setnai provides a rare empirical system not only for linking early developmental processes to intraspecific sexual variation in vertebrate body plans but also as a powerful model to investigate the developmental basis of body plan variation across species.
The vertebrate ahsg (alpha 2-HS glycoprotein, also coined fetuin-a) homologs are highly expressed in the liver, and their secreted protein products exert complex systemic effects, including the regulation of biomineralization of soft and skeletal tissues. Here, we report a previously uncharacterized ahsg retrocopy in the allotetraploid frog species Xenopus laevis. We show that this young retrocopy was born from the ahsg.L homeologue less than 10 Mya, and landed in the S subgenome in a locus located between asic2.S and smarcd2.S. The ahsg.L-retrocopy ends with a poly(A) tail, is intronless, and is flanked by target site duplications. While the ahsg.L-retrocopy's ORF is devoid of frameshifts and nonsense mutations, it suffers from a short 5' deletion, eliminating the original start codon and the signal peptide. Remarkably, this truncated ORF lies in frame with an ATG codon contributed by the neighboring genomic sequence, suggesting that the ahsg.L-retrocopy might potentially be expressed and translated into a protein product. Nevertheless, examination of RNA-Seq and proteomic experiments respectively performed on liver and bone tissues did not provide expression evidence for the ahsg.L-retrocopy. We propose that, in spite of its rescued ORF, the ahsg.L-retrocopy is non-functional and can be considered a young pseudogene born from recent retrotransposon activity in the Xenopus laevis lineage.
Homeodomain transcription factors share an ancient helix-turn-helix DNA-binding core yet regulate diverse developmental and reproductive programs across eukaryotes. We curated 355 nonredundant homeodomain structures spanning fungi, animals, and plants, including 118 experimental PDB entries and 237 high-confidence AlphaFold2 models, and performed large-scale structural comparisons using DaliLite5. Structural distances were summarized as a clustering tree visualized in iTOL and interpreted through topology-guided PyMOL superpositions and sequence-logo mapping of conserved positions. Across kingdoms, the canonical three-helix HTH geometry and the recognition-helix framework were strongly conserved, whereas structural diversification was concentrated in interhelical loops, terminal regions, linker segments, and lineage-specific auxiliary modules. Fungal mating-type homeodomains and major animal classes retained conserved recognition-helix architecture despite sequence divergence, while plant WOX, ZF-HD, PHD-associated, and SAWADEE-associated architectures illustrated modular expansion for developmental and chromatin-context integration.
Gcm1 and Gcm2 are paralogous transcription factors in vertebrates that play key roles in the development of pharyngeal-derived epithelia, yet their deployment across vertebrate lineages remains incompletely understood. While Gcm2 shows deeply conserved pharyngeal expression across gnathostomes, Gcm1 has been mainly characterized in mammals, where it exhibits broader expression patterns. How Gcm1 is deployed in non-mammalian vertebrates has remained unexplored. Here, we performed a comparative analysis of Gcm1 expression in cartilaginous fishes, non-teleost actinopterygians, and amphibians. RNA in situ hybridization revealed conserved Gcm1 expression in gill epithelia across these taxa. Parallel analyses showed that Gcm2 is also expressed in gill epithelia, with overlapping but distinct spatial patterns. In addition, Gcm1 showed lineage-specific expression in bichir embryos, including strong expression in external gills and scattered epithelial cells in the yolk-sac membrane. In the external gills, Gcm1-positive cells possess vacuole-like cytoplasmic structures, suggesting a previously unrecognized epithelial cell population. Together, our findings indicate that Gcm1 and Gcm2 share ancestral expression in pharyngeal epithelia but have followed distinct evolutionary trajectories, with Gcm1 exhibiting greater lineage-specific diversification.
Reproductive division of labour is a key feature underlying the remarkable success of ants, where a reproductive queen caste and non-reproductive worker caste develop from a totipotent egg or larva. The number of ovarioles that develop after the egg or larva is determined to be a queen or worker caste ultimately determines their reproductive potential. Yet since very early descriptions of ant larval ovaries made by Ezhikov (1923) and Brian (1950s), the developmental basis of ovariole number dimorphism in ants has received little attention. Here, we revisit their work in light of more recent knowledge from Drosophila melanogaster, where terminal filaments (TFs) in the larval ovary determine ovariole number on a one-to-one basis. Ezhikov and Brian observed that queen and worker larval ovaries develop the same number of TFs, but in the worker caste, they 'bundle' together to form a single ovariole. Using in situ hybridisation chain reaction (HCR) on multiple queen and worker larval stages, we confirm this bundling process is present in two derived ant species with ovariole dimorphism, but is absent in a species that lacks it. Our findings therefore suggest that this terminal filament bundling reflects a mechanism evolved within ants to regulate differences in worker ovariole number between castes independently of overall number of terminal filaments. This work sheds fresh light on historical ant research and sets up future work investigating the origins and regulation of this putative mechanism.
