Expression and localization of the transcription factor JunD in the duct system of mouse submandibular gland

We studied the expression and localization of JunD, a component of the transcription factor activator protein-1 (AP-1), in the mouse submandibular gland with immunoblotting and immunohistochemistry. In adult mice, all seven Jun and Fos family members constituting the AP-1 complex were expressed more abundantly in the female gland than in the male gland, and JunD was the most abundant of the members. Immunoreactivity for JunD was localized exclusively in the duct system of the gland, in which it was localized to the nuclei of intercalated duct (ID) cells and a subpopulation of striated duct (SD) cells located adjacent to ID. In contrast, granular convoluted tubule (GCT) cells, which are much more abundant in the male gland, were devoid of JunD. During postnatal development of the male gland, JunD was lost from the duct cells as they differentiated to GCT cells at 3-5 weeks postpartum. When GCT differentiation was induced in adult female gland by testosterone administration, many JunD-negative SD cells were temporarily induced to express JunD after 6-24 hr, but those cells lost JunD as they completely converted to GCT cells by 48 hr. These results suggested that JunD is involved in the differentiation of the duct system of mouse submandibular gland, in which there is crosstalk between the androgen/androgen receptor system and the AP-1 complex.

Hepatocyte growth factor is essential for migration of myogenic cells and promotes their proliferation during the early periods of tongue morphogenesis in mouse embryos

Temporal and spatial occurrence of hepatocyte growth factor (HGF) and its cognate receptor c-Met in the mouse mandibular development was investigated by immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction. HGF was first recognized in the mesenchymal cells of the first branchial arch at the 10th day of gestation (E10), before tongue formation, whereas HGF receptor (c-Met) -positive myogenic cells first appeared at E11 in the center of mandibles. By E12, HGF turned to be colocalized with c-Met in the differentiating tongue myoblasts. Between E14 and E16, HGF disappeared, whereas c-Met remained, in the tongue myoblasts. The levels of HGF mRNA in the developing tongue decreased in accordance with the increase of desmin mRNA levels from E11 to E17. These in vivo results strongly suggest that the HGF/c-Met system takes part in the earlier stages of tongue development. To elucidate this hypothesis, the antisense oligodeoxyribonucleotide (A-ODN) for mouse HGF mRNA was added to the organ culture system of mandible with serumless, defined medium. Mandibular arches from E10 mouse embryos were cultured at 37 degrees C for 10 days in the absence or presence of A-ODN, control (sense) oligonucleotide (C-ODN), or A-ODN plus recombinant HGF. In the control mandibular explants cultured without HGF or ODN, the anterior two-third of the tongue derived from the first branchial arch was formed. It contained abundant desmin-positive myoblasts and was equivalent to the tongue of E14-E15. In contrast, in the presence of A-ODN in the medium, neither the swelling nor myogenic cells were found in the tongue-forming region of explants, and myogenic cells accumulated behind the tongue-forming region. Such dysplasia of tongue was never induced in the presence of C-ODN or A-ODN plus recombinant HGF in the medium. The effect of A-ODN appeared to be developmental stage-specific, because tongue dysplasia occurred when A-ODN was present during the earlier 4 days but not during the later 4 days of the culture. Furthermore, recombinant HGF added to the culture without ODNs during the earlier 4 days caused elevation in the number of mitotic myoblasts. These results suggest that HGF regulates both the migration and proliferation of myogenic cells during the earlier stages of tongue development.

Transient occurrence of 27 kDa heat-shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland

It has been suggested that the 27 kDa heat-shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27-immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3-week-old rats for 7 days, the number of Hsp27-positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3-4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants.