31 research outputs found
Evolution and functional plasticity of vertebrate class V POU proteins in pluripotency.
Oct4, a transcription factor belonging to the fifth class of POU proteins (POUV),
plays essential roles in the maintenance of pluripotency, differentiation and the generation of
induced pluripotent stem cells (iPSCs). Oct4 regulates two levels of pluripotency, which are
distinguished by their gene expression profiles and epigenetic status, namely the naĂ¯ve and
primed state of pluripotency. Embryonic stem cells (ESCs) and embryonic germ cells
(EGCs), which are isolated from inner cell mass and primordial germ cells in the embryo,
respectively, are in vitro models in which the naĂ¯ve state is propagated through self-renewal.
Epiblast stem cells (EpiSCs) and traditional human ESCs have gene expression profiles that
are closest to the post-implantation epiblast, which is closer to embryonic differentiation, and
exhibit a primed state of pluripotency. As Oct4 is important for pluripotency in all these cell
types, where it regulates different targets, it appears to have two distinct sets of functions,
namely germ cell/naĂ¯ve ESC-like activity and epiblast/primed pluripotency-like activity.
Based on protein sequences and syntenic gene analysis, Oct4/POUV homologs of jawed
vertebrates can be classified into two subfamilies: POU5F1 and POU5F3, which are thought
to originate from a genome duplication event that occurred in a common ancestor. Most
extant vertebrates have lost one of these paralogs, while a small fraction, including
coelacanths, axolotls, turtles, and marsupials, retains both POUV forms.
In my thesis, I investigated the gene duplication event that underlies divergence of
POU5F1 and POU5F3 in both expression pattern and specialised function. In particular, I
focused on species that have retained both genes and asked whether POUV functional
divergence correlates with ancestral origin. To test the function of POU5F1 and POU5F3, I
substituted endogenous mouse Oct4/Pou5f1 with different POUV proteins using a cell line in
which endogenous Oct4 expression can be silenced with tetracycline (ZHBTc4). Results
showed that POU5F1 proteins had a greater capacity to support naĂ¯ve ESC pluripotency and
self-renewal than POU5F3 proteins. Global transcriptome analysis of the POUV-rescued
ESC lines revealed that coelacanth POU5F1 protein regulates gene expression in a similar
manner to mouse Oct4, in that genes involved in stem cell maintenance, reproduction and
development are upregulated in ESCs rescued by POU5F1, but not POU5F3. Coelacanth
POU5F3 rescued lines, however, expressed genes involved in various cell differentiation
programs, including cell adhesion (e.g. E-cadherin and N-cadherin). This suggests that
POU5F3 plays a role in primed pluripotency, while POU5F1 regulates naĂ¯ve pluripotency.
However, there is one POU5F3 factor that rescues ESCs like Oct4, the Xenopus
gene Xlpou91 (Pou5f3.1). In Xenopus, a further duplication of POU5F3 gene enabled
specialization, and Xlpou91 is expressed specifically in the primordial germ cells. Xlpou25
(Pou5f3.2) exhibits epiblast-specific activities and lacks the capacity to maintain naĂ¯ve ESC
pluripotency, similar to other POU5F3 proteins. This functional distinction between the
different Xenopus POUV paralogs enabled us to address how specific Oct4 functions (germ
cell-like versus epiblast-like activity) are related to the induction of pluripotency. To address
this question, mouse Oct4 was replaced by either Xlpou91 or Xlpou25 in murine cellular
reprogramming using a Nanog-GFP reporter line to monitor iPSC generation. Results
showed that Xlpou91 and mouse Oct4 were required at similar levels to reprogram somatic
cells toward iPSCs and reprogrammed cells emerged with similar kinetics. Conversely,
Xlpou25 was required at higher expression levels and the resulting iPSCs appeared at a later
timepoint, while the pluripotent population in these cultures appeared to be less stable and
more prone to differentiate. I found that this phenotype of enhanced differentiation in
Xlpou25 reprogrammed cultures may be a product of a different set of immediate early
genes induced at the first stages of differentiation. Global transcriptome analysis of the naĂ¯ve
ESC-like pluripotent subpopulation of these iPSC lines confirmed the capacity of all
Xenopus POUVs to drive reprogramming towards the pluripotent state. However, the gene
sets induced by both Xlpou91 and mouse Oct4, but not Xlpou25, were somewhat enriched
for genes involved in reproduction, emphasizing the segregated role of Xlpou91 as a germ
cell specific POUV protein.
Lastly, I explored the evolutionary origin of these two POUV paralogs and
attempted to identify a POUV-related gene in jawless vertebrate (cyclostomes). Based on in
silico analysis of genomic and transcriptome databases, my collaborators and I were able to
identify a single POUV gene in the Japanese/arctic lamprey, thus providing the first insight
into the origin of gnathosome POUV genes
Histological organization of tephritid fruit flies (Diptera, Tephriridae) from Thailand
The structural evidence of tephritids, notably Bactrocera albistrigata, B. dorsalis, B. umbrosa, Zeugodacus cucurbitae,
and Z. tau complex were explored using histology. These tephritids' male reproductive organs comprised two testes, ducts with
deferent ducts, seminal vesicles, and tubular exocrine glands. The testicular follicle was investigated as a cyst during four stages
of spermatogenesis (spermatogonium, spermatocyte, spermatid, and spermatozoa). Similarly, the female reproductive systems of
these fruit flies were morphologically identical, with a pair of ovaries containing seven meroistic ovariole types. There was also a
spermatheca, two lateral oviducts, a common oviduct, and a genital chamber identified. Tephritids have digestive systems
(foregut, midgut, and hindgut), excretory systems (malpighian tubules), neural systems, integumentary systems (cuticle and
epidermis), and adipose tissue. These data are not only significant and publicly available, but they can also be used in future
studies such as on histopathology, ecotoxicological assays, and phylogenic characteristics
Histopathological observation and health status of the zebra-snout seahorse Hippocampus barbouri Jordan & Richardson, 1908 in captivity
The health status of the zebra-snout seahorse, Hippocampus barbouri in captivity has been required for approval for aquaculture. In this study, we investigated the histopathological appearance of three vital organs including gill, kidney and liver in captive H. barbouri during its juvenile and adult stages, by using histological techniques. In juveniles from stage 14-days (100% prevalence) towards stage 30-days adults (100% prevalence), the gills exhibited intraepithelial edema and necrosis while hepatic tissue showed evidence of intracytoplasmic vacuoles. In addition, histological alteration to renal tissues was observed the degeneration of renal tubules, the presence of melanomacrophage, and the infection of trematode parasites. The parasites were found in stage 30-days adult fish in the kidney (33.3 % prevalence). Taken together, this study highlights the issue of health in captive rearing of H. barbouri, in particular histopathological alterations in gill, liver and kidney tissues, suggesting that aquaculture of this seahorse species requires improved methods and protocols for maintenance and preventing infection
The diversity of acorn barnacles (Cirripedia, Balanomorpha) across Thailand’s coasts: The Andaman Sea and the Gulf of Thailand
The acorn barnacle is a sessile crustacean, inhabiting the intertidal areas of tropical and temperate regions worldwide. According to current practices on Cirripedia morphology, shell, opercular valves, and arthropodal characters including cirri and mouthparts are used as a tool for taxonomic classification, and using these characteristics the present study aimed to provide better resolution for the barnacle diversity and geographical distribution within coastlines of Thailand: the Andaman Sea and the Gulf of Thailand. A total of ten species belonging to three families (Chthamalidae, Tetraclitidae, and Balanidae) were identified in this study. Subsequently, five species were newly recorded for the first time from Thailand’s coasts: Newmanella spinosus Chan & Cheang, 2016, Euraphia hembeli Conrad, 1837, Euraphia depressa (Poli, 1795), Tetraclita kuroshioensis Chan, Tsang & Chu, 2007, and Tetraclita singaporensis Chan, Tsang & Chu, 2007. The others, already mentioned in previous records, include: Tetraclita squamosa (Bruguière, 1789), Chthamalus malayensis Pilsbry, 1916, Amphibalanus amphitrite (Darwin, 1854), Amphibalanus reticulatus (Utinomi, 1967), and Megabalanus tintinnabulum (Linnaeus, 1758). Interestingly, acorn barnacles along the Andaman Sea occur abundantly, and are much higher in number of species (up to 8 species) than those found in the Gulf of Thailand’s coast (up to 6 species). This biased trend of species’ preferences is possibly due to the differences in oceanographic nature between two coastlines and the history of barnacle colonization
The diversity of acorn barnacles (Cirripedia, Balanomorpha) across Thailand’s coasts: The Andaman Sea and the Gulf of Thailand
The acorn barnacle is a sessile crustacean, inhabiting the intertidal areas of tropical and temperate regions worldwide. According to current practices on Cirripedia morphology, shell, opercular valves, and arthropodal characters including cirri and mouthparts are used as a tool for taxonomic classification, and using these characteristics the present study aimed to provide better resolution for the barnacle diversity and geographical distribution within coastlines of Thailand: the Andaman Sea and the Gulf of Thailand. A total of ten species belonging to three families (Chthamalidae, Tetraclitidae, and Balanidae) were identified in this study. Subsequently, five species were newly recorded for the first time from Thailand’s coasts: Newmanella spinosus Chan & Cheang, 2016, Euraphia hembeli Conrad, 1837, Euraphia depressa (Poli, 1795), Tetraclita kuroshioensis Chan, Tsang & Chu, 2007, and Tetraclita singaporensis Chan, Tsang & Chu, 2007. The others, already mentioned in previous records, include: Tetraclita squamosa (Bruguière, 1789), Chthamalus malayensis Pilsbry, 1916, Amphibalanus amphitrite (Darwin, 1854), Amphibalanus reticulatus (Utinomi, 1967), and Megabalanus tintinnabulum (Linnaeus, 1758). Interestingly, acorn barnacles along the Andaman Sea occur abundantly, and are much higher in number of species (up to 8 species) than those found in the Gulf of Thailand’s coast (up to 6 species). This biased trend of species’ preferences is possibly due to the differences in oceanographic nature between two coastlines and the history of barnacle colonization