Glenda M. Wright

Transformation of the endostyle of the anadromous sea lamprey, Petromyzon marinus L., during metamorphosis ☆: I. Light microscopy and autoradiography with 125I

Abstract Routine light microscopy and autoradiography with 125 I were used to examine the transformation in structure and iodine-binding capacity of the endostyle throughout (stages 1 to 4) metamorphosis in the anadromous sea lamprey, Petromyzon marinus L. The endostyle began to transform prior to the first external signs of metamorphosis (prometamorphosis) and was already replaced by thyroid follicles by the end of stage 2 of metamorphosis. Many of these follicles appeared to have formed as a result of proliferation of the epithelia (type II and V cells) at the angle of the original lumina of the endostyle. However, it is possible that all cell types of the ammocoete endostyle, with the exception of the type I cells, may be involved in the formation of at least some follicles. The colloid of the newly formed follicles was not stainable with periodic acid-Schiff, suggesting that the thyroglobulin which is synthesized or released by metamorphosing lamprey may have different chemical properties than thyroglobulin of the adult. Large numbers of pigmented granules within some of the remaining epithelial cells may reflect their involvement in the storage of thyroid hormone or in its release during metamorphosis. 125 I was bound within the transforming endostyle and its replacement throughout metamorphosis, but the localization of the radioiodine varied during the reconstruction. During prometamorphosis and early stage 1 the distribution of iodine resembled that of ammocoetes. In subsequent stages, at first not all follicles demonstrated the ability to bind iodine (end of stage 2), but there was a progressive increase in binding to the end of the metamorphic period. It is suggested that the binding of iodine in the newly formed follicles reflects the involvement of cells of the ammocoete endostyle. There also appears to be a variable differentiation of cells within the developing follicles.

Immunocytochemical demonstration of growth hormone, prolactin and somatostatin-like immunoreactivities in the brain of larval, young adult and upstream migrant adult sea lamprey, Petromyzon marinus

SummaryGrowth hormone, prolactin and somatostatinlike immunoreactivities were demonstrated in the brains of larval, young adult (parasitic) and upstream migrant adult sea lampreys, Petromyzon marinus, by means of immunoperoxidase techniques. Growth hormone (GH) and prolactin (PRL) were observed within separate perikarya in the nucleus praeopticus, within fibers in the commissura praeinfundibularis, and in nerve endings within the neurohypophysis of larval and adult-stage lampreys. Cell bodies demonstrating immunoreactive growth hormone were more numerous than those reactive for prolactin. Unlike in the upstream migrant adult lamprey, no GH or PRL was demonstrated in the adenohypophysis of larval or parasitic lamprey.Somatostatin (SRIF)-like immunoreactive neurons were demonstrated in the nucleus commissurae praeinfundibularis, anterior and posterior pars ventralis hypothalami, pars dorsalis thalami, and the tegmentum motorium rhombencephali of larval, parasitic and upstream migrant adult lampreys. Many of the SRIF containing neurons within the hypothalamus were cerebrospinal fluid (CSF)-contacting cells. SRIF fibers were found throughout most of the brain predominating within the nucleus praeopticus, pars ventralis hypothalami, and the nucleus interpeduncularis. No SRIF immunoreactivity was found within the neurophyophysis. The possible functions of these peptides within the brain of the lamprey are discussed.

Lamprin: A new vertebrate protein comprising the major structural protein of adult lamprey cartilage

Chemical analysis of lamprey cartilage showed that its major constituent was a newly defined structural protein termed lamprin. Amino acid analysis of lamprin revealed that it has a unique composition which is distinct from previously identified structural proteins.

Immunocytochemical study of growth hormone, prolactin, and thyroid-stimulating hormone in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration

Immunoreactivity to growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) was found in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration, by immunoperoxidase techniques with antisera to mammalian pituitary hormones. Cross-reactivity to GH and PRL was found in two different cell populations in the proximal pars distalis. Specific immunostaining for GH and PRL was absent in other parts of the lamprey pituitary. Immunoreactive TSH cells were located only in the rostral pars distalis, and corresponded in shape and size to the large basophils in this region of the lamprey pituitary. These results suggest that mammalian-like GH, PRL, and TSH are produced in the pituitary of the lamprey.

Transformation of the endostyle of the anadromous sea lamprey, Petromyzon marinus L., during metamorphosis. II. Electron microscopy

Electron microscopy was used to follow the transformation of the endostyle to a thyroid gland in the anadromous sea lamprey, Petromyzon marinus L., throughout metamorphosis (stages 1–7). Transformation of the larval (ammocoete) endostyle begins at the first signs of external change (stages 1–2), and the adult form of the gland is reached by stage 5. Only slight modifications of the gland accompany further development to the end of metamorphosis.

Immunocytochemical study of luteinizing hormone in the pituitary of the sea lamprey, Petromyzon marinus L., during its upstream migration

SummaryA mammalian-like immunoreactive luteinizing hormone (LH) has been localized in the cytoplasm of cells in the meso-adenohypophysis of the sea lamprey, Petromyzon marinus L. Specific staining for LH was absent in other regions of the lamprey pituitary.

Immunocytochemical localization of thyroglobulin in the transforming endostyle of anadromous sea lampreys, Petromyzon marinus L., during metamorphosis.

Abstract Light and electron microscopic immunocytochemistry was used to detect the localization of thyroglobulin (TG) in the transforming endostyle of the anadromous sea lampreys, Petromyzon marinus L., during metamorphosis. TG is found within the transforming endostyle throughout metamorphosis (stages 1 to 7) and in early stages (1–2) staining for TG is similar to that observed in the endostyle of the ammocoete. By stage 3, most of the TG is found in large bodies that accumulate within type 3 cells. At stage 4 immunostaining for TG is found within the epithelial cells of the transforming endostyle and in the lumina of some of the first formed follicles. Most of the follicular lumina contain TG by the end of metamorphosis (stage 7). TG in the young parasitic adult lamprey is localized within the follicular lumina, colloid droplets, and occasionally in large bodies found in some of the follicular epithelial cells.

Light and electron microscopic immunocytochemical localization of thyroglobulin in the thyroid gland of the anadromous sea lamprey, Petromyzon marinus L., during its upstream migration

SummaryAntibodies made against thyroglobulin (TG) were used in an immunocytochemical study for the light and electron microscopic localization of TG in the thyroid gland of the anadromous sea lamprey, Petromyzon marinus, during its upstream migration. TG was found in the follicular lumen and in some colloid droplets within the follicular cells. Except for an immunoreactive product observed in a small portion of the interstitial connective tissue, the location of TG in the lamprey was similar to that in the thyroid of the rat.

Variation in serum levels of thyroxine in anadromous larval lampreys, Petromyzon marinus L

Circulating levels of thyroxine in samples of fresh sera taken from larval anadromous sea lampreys (Petromyzon marinus L.) were measured by means of radioimmunoassay. Average sera thyroxine levels varied from a minimum of 4.92 μg/100 ml in March to a high of 18.49 μg/100 ml in June. Variations are discussed in relation to temperature, metabolic state of the animal, and the time of metamorphosis.

Transformation of mucocartilage to a definitive cartilage during metamorphosis in the sea lamprey, Petromyzon marinus

An ultrastructural analysis of the development of adult piston (tongue) cartilage in the ventromedial longitudinal bar (VMLB), an area of larval mucocartilage, was undertaken in the lamprey, Petromyzon marinus, in order to clarify the relationship between these two unique larval and adult connective tissues. At the onset of metamorphosis, the mucocartilage fibroblasts dedifferentiate into a “mesenchymal” cell type. Migration of unspecialized cells from surrounding tissues plays an important role in the development of a cellular “embryonic” tissue in the VMLB. Degradation of the mucocartilage extracellular matrix (ECM) by the unspecialized cells seems to occur prior to cartilage differentiation. This event is followed by the appearance of a blastema of undifferentiated cells, which expands by proliferation of cells in the core of the VMLB. The cells of the blastema subsequently differentiate into chondroblasts, which secrete adult ECM components consisting of 20‐nm nonbanded fibrils, electron‐dense branched lamprin fibrils, and proteoglycan. The present study suggests that mucocartilage, as a primitive or embryonic connective tissue, temporarily specializes to act as a skeletal support during larval life. Once metamorphosis is initiated, this tissue resumes an embryonic character (mesenchymal) and cartilage histogenesis takes place. The mechanism of cartilage development within the lamprey VMLB is similar to that observed in the chondrogenic system of higher vertebrates.