Ovarian cycle in Devario aequipinnatus with emphasis on oogenesis

Craniofacial diversity across Danionins and the effects of TH status on craniofacial morphology of two Danio species

The model zebrafish ( Danio rerio ) belongs to the Danioninae subfamily with a range of informative phenotypes. However, the craniofacial diversity across the subfamily is not fully described. To better understand craniofacial phenotypes across Danioninae we used microCT and 3D geometric morphometrics to capture skull shapes from nine species. The Danio species examined showed largely similar skull shapes, although D. aesculapii , the sister species to D. rerio showed a unique morphology. Two non- Danio species examined, Chela dadiburjori and Devario aequipinnatus showed distinct skull morphologies unique from those of other species examined. Thyroid hormone regulates skeletal development and remodeling, and we asked if changes in developmental thyroid hormone metabolism could underlie some of the craniofacial diversity across Danioninae. We reared two Danio species under altered thyroid profiles, finding that hypothyroid individuals from both species showed corresponding morphological shifts in skull shape. Hypothyroid Danios showed skull morphologies closer to that of Chela and unlike any of the examined wild-type Danio species. We provide an examination of the evolved craniofacial diversity across Danioninae, and demonstrate that alterations to thyroid hormone have the capacity to create unique skull phenotypes.

Oogonial proliferation and early oocyte dynamics during the reproductive cycle of two Clupeiform fish species

Although oogonial proliferation continues in mature females in most teleosts, its dynamics and the transformation of oogonia to early meiotic oocytes during the reproductive cycle have received little attention. In the present study, early oogenesis was examined throughout the reproductive cycle in two Clupeiform fishes, the Mediterranean sardine, Sardina pilchardus, and the European anchovy, Engraulis encrasicolus. Observations using confocal laser scanning microscopy (CLSM) provided extensive information on markers of oogonial proliferation (mitotic divisions, oogonia nests) and meiotic prophase I divisions of oocyte nests (leptotene, zygotene, pachytene, diplotene) in ovaries of different reproductive phases. In sardine, oogonial proliferation persisted throughout the entire reproductive cycle, whereas in anchovy, it was more pronounced prior to (developing ovaries) and after (resting ovaries) the spawning period. Anchovy exhibited a higher rate of meiotic activity in developing ovaries, whereas sardine exhibited a higher rate in resting ovaries. The observed differences between the two species can potentially be attributed to different seasonal patterns of energy allocation to reproduction and the synchronization between feeding and the spawning season.

Reproductive cycle of the tetra Astyanax bimaculatus (Characiformes: Characidae) collected in Amazonian streams

A histological characterization of gonadal development in the tetra Astyanax bimaculatus was performed, aimed at determining its reproductive cycle in streams localized inside the Amazonian forest. Collections were carried out monthly from August 2017 to July 2018 at the Zoobotânica Foundation of Marabá, PA. Collected specimens were weighed and measured, and their gonads and liver were removed and weighed to calculate gonadosomatic and hepatosomatic indexes. Gonads were fixed and treated for routine histology for light microscopy. Materials were stained with toluidine blue and haematoxylin and eosin. The Amazonian A. bimaculatus species presented two reproductive periods in the year, one at the end of the winter season and another during the summer. Females showed an asynchronous development of their oocytes and only two reproductive phases of development were observed during the whole period 'developing' and 'spawning capable'. Males presented cystic spermatogenesis, with an anastomosing tubular testis containing spermatogonia spread along the germinal epithelium (unrestricted spermatogonial). These morphological characteristics are considered phylogenetically more primitive. Male specimens were observed to have five different phases during the period: immature, initial maturation, mid maturation, final maturation and regression. The huge fluctuations in Amazonian streams was observed, in which water volumes varied considerably across seasons, culminating even in total drought. In spite of this, A. bimaculatus could be found during all seasons, showing its impressive reproductive adaptation to its conditions.

Genome-wide DNA methylation analysis of pituitaries during the initiation of puberty in gilts

It has been widely recognized that the early or delayed puberty appears to display harmful effects on adult health outcomes. During the timing of puberty, pituitaries responds to the hypothalamus and then introduce the following response of ovaries in hypothalamic-pituitary-gonadal axis. DNA methylation has been recently suggested to regulate the onset of puberty in female mammals. However, to date, the changes of DNA methylation in pituitaries have not been investigated during pubertal transition. In this study, using gilts as the pubertal model, the genome-scale DNA methylation of pituitaries was profiled and compared across Pre-, In- and Post-puberty by using the reduced representation bisulfite sequencing. We found that average methylation levels of each genomic feature in Post- were lower than Pre- and In-pubertal stage in CpG context, but they were higher in In- than that in Pre- and Post-pubertal stage in CpH (where H = A, T, or C) context. The methylation patterns of CpHs were more dynamic than that of CpGs at the location of high CpG content, low CpG content promoter genes, and differently genomic CGIs. Furthermore, the differently genomic CGIs were likely to show in a similar manner in CpG context but display in a stage-specific manner in the CpH context across the Pre-, In- and Post-pubertal stage. Among these pubertal stages, 5 kb upstream regions of the transcription start sites were protected from both CpG and CpH methylation changes. 12.65% of detected CpGs were identified as the differentially methylated CpGs, regarding 4301 genes which were involved in the fundamental functions of pituitaries. 0.35% of detected CpHs were identified as differentially methylated CpHs, regarding 3691 genes which were involved in the biological functions of releasing gonadotropin hormones. These observations and analyses would provide valuable insights into epigenetic mechanism of the initiation of puberty in pituitary level.