Formation Of Head Structures Research Articles

Expression and regulation of Noggin4 gene in chicken ovarian follicles and its role in the proliferation and differentiation of granulosa cells

As a member of Noggin family, Noggin4 is reported to play an important role in the formation of head structure during the embryo development of Xenopus laevis and chicken. We previously detected an increase of Noggin4 transcript in the granulosa cells of chicken hierarchal follicles (Post-GCs) compared to pre-hierarchal follicles (Pre-GCs) by ONT transcriptome sequencing. To further clarify the role of Noggin4 in chicken follicle selection, in this study, we investigated its expression, regulation and function in follicles and granulosa cells. The mRNA expression of chicken Noggin4 exhibited dynamic changes during follicle development. It was significantly higher in the small yellow follicles than in the small white, F6, F5 and F4 follicles, and also increased in Post-GCs than in Pre-GCs. The Noggin4 mRNA could be stimulated by follicle stimulating hormone (FSH) and bone morphogenetic protein 4 (BMP4) in both Pre-GCs and Post-GCs. However, the estrogen and progesterone could exert opposing transcriptional regulations on Noggin 4 mRNA in both Pre- and Post-GCs. In chicken Post-GCs, knockdown of Noggin4 by siRNA reduced the mRNA expression of steroidogenic acute regulatory protein (STAR), cytochrome P450 family 11 subfamily A member 1 (CYP11A1), but increased that of Wnt family member 4 (Wnt4), while overexpression of Noggin4 significantly decreased the mRNA expression of Wnt4 but had no marked effects on that of STAR and CYP11A1. Moreover, Noggin4 significantly decreased the mRNA expression of BMP4 in both Pre-GCs and Post-GCs. Overexpression of Noggin4 inhibited the proliferation of both Pre-GCs and Post-GCs. These data collectively suggest an important role of Noggin4 in chicken follicle selection, especially on the proliferation of granulosa cells.

Secreted protein Noggin4 participates in the formation of forebrain structures in Xenopus laevis by inhibiting the Wnt/beta-catenin signaling pathway

Noggin proteins are important regulators of the early development of the vertebrate neural system. Previously, it has been traditionally thought that vertebrates have only one noggin gene (Noggin1), whose main function is the inhibition of BMP signaling pathway during the formation of dorsoventral polarity in embryos. Then other proteins of this family were discovered, and the studies of Noggin2 protein showed that noggin proteins also participate in the modulation of Nodal/Activin and Wnt/beta-catenin signaling pathways in the early development of amphibian head structures. The purpose of this study is to investigate the properties of another noggin protein, Noggin4. We proved that Noggin4 plays an important role in the formation of head structure in clawed frog, since it inhibits the activity of Wnt/beta-catenin signaling pathway. At the same time, unlike Noggin1 and Noggin2, Noggin4 does not inhibit the activity of TGF-beta signaling pathways (BMP and Nodal/Activin).

Temporal and spatial expression analysis of peripheral myelin protein 22 (Pmp22) in developing Xenopus

Peripheral myelin protein 22 (Pmp22), a member of the junction protein family Claudin/EMP/PMP22, contributes to the formation and maintenance of myelin sheaths in the peripheral nervous system. Apart from the establishment and maintenance of peripheral nerves, Pmp22 and its family member have also participated in a broad range of more general processes including cell cycle regulation and apoptosis during development. Pmp22 has been identified from several vertebrate species including mouse, human and zebrafish. However, Pmp22 has not been identified from Xenopus embryos yet. In this paper, we cloned Pmp22 from Xenopus laevis and evaluated its expression during embryogenesis. We found that Pmp22 was initially expressed in the mesoderm and cement gland during the neurula stage. At early tailbud stage, strong expression of Pmp22 was detected in the trigeminal and profundal ganglia as well as developing somites and branchial arches. Later in development, Pmp22 was expressed specifically in cranio-facial cartilage, roof plate and floor plate of the developing brain, otic vesicle and lens. Pmp22 is also strongly expressed in the developing trachea and lungs. Based on its expression in facial tissues, we propose that Pmp22 may be involved in the formation of head structure in addition to the maintenance of functional peripheral nerves in Xenopus embryos.

The zinc finger transcriptional repressor Blimp1/Prdm1 is dispensable for early axis formation but is required for specification of primordial germ cells in the mouse

Blimp1, a zinc-finger containing DNA-binding transcriptional repressor, functions as a master regulator of B cell terminal differentiation. Considerable evidence suggests that Blimp1 is required for the establishment of anteroposterior axis formation and the formation of head structures during early vertebrate development. In mouse embryos, Blimp1 is strongly expressed in axial mesendoderm, the tissue known to provide anterior patterning signals during gastrulation. Here, we describe for the first time the defects caused by loss of Blimp1 function in the mouse. Blimp1 deficient embryos die at mid-gestation, but surprisingly early axis formation, anterior patterning and neural crest formation proceed normally. Rather, loss of Blimp1 expression disrupts morphogenesis of the caudal branchial arches and leads to a failure to correctly elaborate the labyrinthine layer of the placenta. Blimp1 mutant embryos also show widespread blood leakage and tissue apoptosis, and, strikingly, Blimp1 homozygous mutants entirely lack PGCs. At the time of PGC allocation around 7.25 days post coitum, Blimp1 heterozygous embryos exhibit decreased numbers of PCGs. Thus Blimp1 probably acts to turn off the default pathway that allows epiblast cells to adopt a somatic cell fate, and shifts the transcriptional program so that they become exclusively allocated into the germ cell lineage.

Network of gene function and its modification by environmental factors and epigenetic events in the formation of head structures

A few important aspects when considering the etiology and pathogenesis of congenital anomalies are reviewed and discussed using examples related to morphogenesis of the head and craniofacial structures. Namely, the network and cascade of gene functions, modification by environmental or exogenous factors, and morphogenetic characteristics (epigenetic events) of each body part as the result of a genetic program.

Designation of the Anterior/Posterior Axis in Pregastrula Xenopus laevis

A new fate map for mesodermal tissues in Xenopus laevis predicted that the prime meridian, which runs from the animal pole to the vegetal pole through the center of Spemann's organizer, is the embryo's anterior midline, not its dorsal midline (M. C. Lane and W. C. Smith, 1999, Development 126, 423–434). In this report, we demonstrate by lineage labeling that the column 1 blastomeres at st. 6, which populate the prime meridian, give rise to the anterior end of the embryo. In addition, we surgically isolate and culture tissue centered on this meridian from early gastrulae. This tissue forms a patterned head with morphologically distinct ventral and dorsal structures. In situ hybridization and immunostaining reveal that the cultured heads contain the anterior tissues of all three germ layers, correctly patterned. Regardless of how we dissect early gastrulae along meridians running from the animal to the vegetal pole, both the formation of head structures and the expression of anterior marker genes always segregate with the prime meridian passing through Spemann's organizer. The prime meridian also gives rise to dorsal, axial mesoderm, but not uniquely, as specification tests show that dorsal mesoderm arises in fragments of the embryo which exclude the prime meridian. These results support the hypothesis that the midline that bisects Spemann's organizer is the embryo's anterior midline.