Myogenic Determination and Differentiation of the Mouse Palatal Muscle in Relation to the Developing Mandibular Nerve

Abstract

The vertebrate palatal muscles are derived from the cranial paraxial mesoderm and start myogenesis by the expression of myogenic regulatory factors (MRFs). Predetermined myogenic cells migrate from the cranial paraxial mesoderm into the branchial arches, followed by myogenic differentiation. The objective of this study was to elucidate whether the determination, migration, and differentiation of myogenic cells during the myogenesis of the palatal muscles, particularly the tensor veli palatini (TVP), are related to the extending mandibular nerve in mouse embryos. By immunohistochemical staining at embryonic day (E) 9.5, MyoD1 and myogenin have been expressed in the mandibular arch, into which the mandibular nerve had not yet extended. At E11.5, these myogenic cells encircled the extending mandibular nerve and were distributed from the distal and lateral to the trigeminal ganglion and into the mandibular arch to form the muscle plate, a girdle-like structure. By E12.5, these myogenic cells lost their girdle-like pattern, vacated the trunk area of the mandibular nerve, and were separated into several incompletely divided masses encircling the collateral branches of the mandibular nerve. The TVP started differentiation at E13.5 with the appearance of myofilaments and acetylcholinesterase (AchE), whereas the other palatal muscles began differentiation at E14.5. We defined the differentiation process of mouse palatal muscles into five stages based on the present findings. These results suggest that the determination and initial migration of the palatal myogenic cells into the mandibular arch occur before the mandibular nerve extends out of the trigeminal ganglion, whereas the myogenic cells migrating into the final sites of differentiation intimately relate to the extending nerve.

Two upstream enhancers collaborate to regulate the spatial patterning and timing of MyoD transcription during mouse development

“…Rather, expression of Ϫ24lacZ at E9.5 likely reflects cooperation between regulatory sequences in fragment 3 and the DRR (and perhaps other, unknown regulatory elements) combined with the greater sensitivity and resolution of ␤-gal histochemistry, and probably approximates the actual time at which MyoD transcription is initiated. This is consistent with detection of MyoD mRNA (whole embryos) and protein (somites and branchial arches) at E9.5 by RT-PCR (Hannon et al, 1992) and immunohistochemistry (Smith et al, 1994;Zhang et al, 1999), respectively. In addition, the early expression of Ϫ24lacZ in occipito-cervical somites is weak relative to the later expression in the hypaxial domain of interlimb somites, which probably explains why this classical Fig.…”

“…The apparent earlier onset of Ϫ24lacZ transgene expression in occipito-cervical somites and branchial arches relative to the in situ detection of MyoD mRNA probably reflects the greater sensitivity and resolution of ␤-gal histochemistry. Previous immunohistochemistry studies have detected MyoD protein by E9.5 in the mandibular arch (Zhang et al, 1999) and anterior somites (Smith et al, 1994), and the pattern of MyoD protein accumulation was consistent with a craniocaudal gradient of expression in somites (see Smith et al, 1994).…”

“…e Staining of the tip of the tongue was not observed until E15.5. f From Zhang et al, 1999. MyoD mRNA is detected by in situ hybridization by E10.5 (present study; Faerman and Shani, 1993).…”

Intracellular Signaling Pathway Activation via TGF-β Differs in the Anterior and Posterior Axis During Palatal Development

“…The tissue in the palatal region can be divided into the bony hard and the muscular soft palates, each having a specialized function, such as occlusion, speech, or swallowing. In the initiation stage of palatogenesis, palatal mesenchyme is mostly composed of neural crest-derived cells in the anterior-posterior axis, and after the palatal shelves are fused, paraxial mesoderm-derived cells migrate into the posterior palate and contribute to palatal muscles with neural crest-derived cells [22][23][24] . Therefore, neural crest-derived cells mostly contribute to palatal mesenchyme in both the anterior and posterior parts until E14.5.…”

Evidences of a role for eukaryotic translation initiation factor 5A (eIF5A) in mouse embryogenesis and cell differentiation

“…An increase in cellular proliferation rate, which is necessary for reaching the weight and size necessary for birth, also occurs at those later times. Some of the events that are known to occur in E13.5 embryos are: differentiation of some neuron subtypes (Butt et al, 2005) and of epidermal cells from the ectoderm (Byrne et al, 1994), retina formation through regulation of retinoic acid production (Matt et al, 2005), differentiation of groups of endothelial and liver cells to definitive hematopoietic cells (Bonnesen et al, 2005;Li et al, 2006), differentiation of cardiomyocytes (Dorner et al, 2005), the beginning of Meckel's cartilage development in the mandibular region (Melnick et al, 2005), and skeletal muscle primary differentiation (Laclef et al, 2003), including differentiation of palatal muscles (Zhang et al, 1999).…”