Limits...
Myogenesis in the basal bilaterian Symsagittifera roscoffensis (Acoela).

Semmler H, Bailly X, Wanninger A - Front. Zool. (2008)

Bottom Line: In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles.No specific statocyst muscles were found.In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Copenhagen, Department of Biology, Research Group for Comparative Zoology, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark. hsemmler@bio.ku.dk.

ABSTRACT

Background: In order to increase the weak database concerning the organogenesis of Acoela - a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans - we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software.

Results: At 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

Conclusion: Compared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.

No MeSH data available.


Related in: MedlinePlus

Adult musculature associated with mouth and genital organs. CLSM micrographs. Anterior is left in all aspects. A. The relative position of the mouth opening (asterisk) and female (fg) and male gonopore (mg) is visible. B-F. The male gonopore is encircled by circular pore muscles (cgm) and the posterior part of the animal shows sagittocysts (sg). C. The musculature associated with the penis is framed. D. Sagittocysts anterior to the male gonopore are indicated. E. The paired false seminal vesicles (fsv) terminate at the male gonopore. F. The female gonopore and the sclerotized bursal nozzle (bn) are visible. The bursal nozzle leads from the seminal bursa to the female genital opening. Sagittocysts in the lateral sides of the body are marked with arrowheads. G. The muscle mantle of the sagittocysts is located below the bodywall muscle grid. H. Detail of the boxed area in (G), showing the sagittocysts in higher magnification. Scale bars: 200 μm (A, E-F), 50 μm (B, C, H), 100 μm (D, G).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2562460&req=5

Figure 7: Adult musculature associated with mouth and genital organs. CLSM micrographs. Anterior is left in all aspects. A. The relative position of the mouth opening (asterisk) and female (fg) and male gonopore (mg) is visible. B-F. The male gonopore is encircled by circular pore muscles (cgm) and the posterior part of the animal shows sagittocysts (sg). C. The musculature associated with the penis is framed. D. Sagittocysts anterior to the male gonopore are indicated. E. The paired false seminal vesicles (fsv) terminate at the male gonopore. F. The female gonopore and the sclerotized bursal nozzle (bn) are visible. The bursal nozzle leads from the seminal bursa to the female genital opening. Sagittocysts in the lateral sides of the body are marked with arrowheads. G. The muscle mantle of the sagittocysts is located below the bodywall muscle grid. H. Detail of the boxed area in (G), showing the sagittocysts in higher magnification. Scale bars: 200 μm (A, E-F), 50 μm (B, C, H), 100 μm (D, G).

Mentions: The female genital pore lies in much closer proximity to the male pore than to the mouth, namely at U70 of the anterior-posterior body axis (Figure 7A, F). The bursal nozzle (sometimes also referred to as "bursa mouthpiece"), which is composed of a sclerotized lamellate stack of cells that form a sperm duct, contains intracellular actin (Figure 7F). The male genital pore is situated almost at the posterior end of the body at U90 of the anterior-posterior body axis (Figure 7A–F). The male gonopore is surrounded by circular muscles (Figure 7A, B, E, F). The muscle grid around the male gonopore is not very regular, since many sagittocyst openings are present in this region. The paired "false seminal vesicles", where sperm masses are accumulated, are situated anterior to the male gonopore and are surrounded by parenchymal muscles (Figure 7E).


Myogenesis in the basal bilaterian Symsagittifera roscoffensis (Acoela).

Semmler H, Bailly X, Wanninger A - Front. Zool. (2008)

Adult musculature associated with mouth and genital organs. CLSM micrographs. Anterior is left in all aspects. A. The relative position of the mouth opening (asterisk) and female (fg) and male gonopore (mg) is visible. B-F. The male gonopore is encircled by circular pore muscles (cgm) and the posterior part of the animal shows sagittocysts (sg). C. The musculature associated with the penis is framed. D. Sagittocysts anterior to the male gonopore are indicated. E. The paired false seminal vesicles (fsv) terminate at the male gonopore. F. The female gonopore and the sclerotized bursal nozzle (bn) are visible. The bursal nozzle leads from the seminal bursa to the female genital opening. Sagittocysts in the lateral sides of the body are marked with arrowheads. G. The muscle mantle of the sagittocysts is located below the bodywall muscle grid. H. Detail of the boxed area in (G), showing the sagittocysts in higher magnification. Scale bars: 200 μm (A, E-F), 50 μm (B, C, H), 100 μm (D, G).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2562460&req=5

Figure 7: Adult musculature associated with mouth and genital organs. CLSM micrographs. Anterior is left in all aspects. A. The relative position of the mouth opening (asterisk) and female (fg) and male gonopore (mg) is visible. B-F. The male gonopore is encircled by circular pore muscles (cgm) and the posterior part of the animal shows sagittocysts (sg). C. The musculature associated with the penis is framed. D. Sagittocysts anterior to the male gonopore are indicated. E. The paired false seminal vesicles (fsv) terminate at the male gonopore. F. The female gonopore and the sclerotized bursal nozzle (bn) are visible. The bursal nozzle leads from the seminal bursa to the female genital opening. Sagittocysts in the lateral sides of the body are marked with arrowheads. G. The muscle mantle of the sagittocysts is located below the bodywall muscle grid. H. Detail of the boxed area in (G), showing the sagittocysts in higher magnification. Scale bars: 200 μm (A, E-F), 50 μm (B, C, H), 100 μm (D, G).
Mentions: The female genital pore lies in much closer proximity to the male pore than to the mouth, namely at U70 of the anterior-posterior body axis (Figure 7A, F). The bursal nozzle (sometimes also referred to as "bursa mouthpiece"), which is composed of a sclerotized lamellate stack of cells that form a sperm duct, contains intracellular actin (Figure 7F). The male genital pore is situated almost at the posterior end of the body at U90 of the anterior-posterior body axis (Figure 7A–F). The male gonopore is surrounded by circular muscles (Figure 7A, B, E, F). The muscle grid around the male gonopore is not very regular, since many sagittocyst openings are present in this region. The paired "false seminal vesicles", where sperm masses are accumulated, are situated anterior to the male gonopore and are surrounded by parenchymal muscles (Figure 7E).

Bottom Line: In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles.No specific statocyst muscles were found.In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Copenhagen, Department of Biology, Research Group for Comparative Zoology, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark. hsemmler@bio.ku.dk.

ABSTRACT

Background: In order to increase the weak database concerning the organogenesis of Acoela - a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans - we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software.

Results: At 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

Conclusion: Compared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.

No MeSH data available.


Related in: MedlinePlus