Biomedical subjects

J L Specker

Publications and source records attributed to J L Specker.

At least 19 recordsLinked to original sources

PubMed2001

Metamorphosis of summer flounder, Paralichthys dentatus: cell proliferation and differentiation of the gastric mucosa and developmental effects of altered thyroidal status.

Summer flounder, like most marine fishes studied to date, are stomachless at first feeding, and subsequently acquire gastric function during the process of metamorphosis. Stomach formation is controlled largely by thyroxine (T4). In the present work we sought to understand gastric organogenesis in terms of cell proliferation and its relationship to histological differentiation. The objectives of the study were (1) to obtain a developmental pattern of cell proliferation in the gastric mucosa and to relate that pattern to the progress of gastric differentiation; and (2) to understand the regulatory role of T4 on cell proliferation and histological differentiation by altering the thyroidal status of the developing larvae. We observed that (1) in normally developing larvae, cell proliferation increased by early metamorphic climax (MC), remained high until mid-MC, and decreased to basal levels by late MC; concomitantly, the gastric glands appeared and differentiated in the fundic mucosa, and were complete by late MC; (2) T4 accelerated the differentiation of gastric glands and mucus neck cells, while inhibiting the concomitant increase in cell proliferation observed in controls; and (3) the goitrogen thiourea inhibited both cell proliferation and gastric differentiation compared to controls. These results indicate that T(4) is necessary for the three-fold increase in cell proliferation that occurs in early metamorphic climax, but that high T4 levels promote differentiation at the expense of proliferation. The observed effects would be consistent with the normal, metamorphosis-related increase in whole body T4.

Animals↗

PubMed2000

Incorporation and metabolism of cortisol in oocytes of tilapia (Oreochromis mossambicus).

The entry and metabolism of 3H-cortisol in oocytes were investigated using isolated follicles of the tilapia (Oreochromis mossambicus) in order to examine the mechanisms of incorporation of maternal hormones into oocytes. The composition of 3H-labeled steroids in the oocyte was analyzed by high-performance liquid chromatography. A significant amount of cortisol was converted to cortisone and an unidentified molecule by the follicular layer. The contents of 3H-cortisol and 3H-cortisone in the oocyte reached an equilibrium level within 12 hr, whereas the content of the unidentified metabolite continued to increase for 36 hr. The total content of the incorporated cortisol and its metabolites was proportional to cortisol in the medium over the concentration range of 5 ng/ml to 5 microg/ml. The amounts of cortisone and the unidentified molecule increased proportionally when the concentration of cortisol in the medium was lower than 500 ng/ml, whereas they reached a plateau when the concentration of cortisol exceeded 500 ng/ml. Cortisol entry was reversible, because 90% of cortisol and cortisone in the oocyte was lost within 18 hr when the medium was changed to that without 3H-cortisol. On the other hand, 50% of the unidentified molecule was preserved at the end of the incubation. In conclusion, the entry of cortisol into the oocyte was considered to be nonspecific and due probably to simple diffusion. However, a considerable amount of cortisol (50-70%) was specifically converted to cortisone and another unidentified molecule during passage through the follicular layer.

Animals↗

PubMed2000

Metamorphosis in the summer flounder, Paralichthys dentatus: thyroidal status influences gill mitochondria-rich cells.

Metamorphosis in the summer flounder (Paralichthys dentatus) is mediated by thyroid hormones (TH) and is accompanied by changes in gill mitochondria-rich cells (MRCs) and in salinity tolerance. Altered thyroid status during larval development and metamorphosis in this species influences salinity tolerance, though the influence of any hormone on MRCs of larval marine teleosts is not known. This study characterized the effect of altered thyroid status on MRC intracellular membranes, mitochondria size and ultrastructure, immunoreactive (ir)-Na(+),K(+)-ATPase, and cell size and density during metamorphosis in summer flounder. Inhibition of metamorphosis with thiourea (30 ppm) (TU, an inhibitor of TH synthesis) inhibited changes in MRCs, producing large "larval" type MRCs with weak reactivity to osmium; large, electron-lucent mitochondria; and weak ir-Na(+),K(+)-ATPase. Replacement of TH with TU + thyroxine-Na salt (100 ppb) rescued the fish from developmental inhibition, producing smaller "juvenile" type MRCs with strong reactivity to osmium; smaller, electron-opaque mitochondria; and strong ir-Na(+), K(+)-ATPase. The findings suggest that TH are necessary for MRCs to change from larval to juvenile form during metamorphosis.

Animals↗

PubMed2000

Paternal mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces: cichlidae): changes in gonadal steroids and potential for vitellogenin transfer to larvae.

The black-chinned tilapia (Sarotherodon melanotheron) is a paternal mouthbrooder. Pairs of adult black-chinned tilapia were raised in freshwater and the males were sampled during the mouthbrooding cycle. Sampling also occurred 10 days after release of the free-swimming fry for comparison. During the first week of incubation of the eggs, total androgens and estradiol were low (<5 and <0.3 ng/ml, respectively). During the second week of brooding, when the eggs have hatched and they are called newly hatched embryos, plasma levels of gonadal steroids increased (13-38 ng androgen/ml and >0.6 ng estradiol/ml). The plasma concentrations of vitellogenin (VTG) in male parents changed during mouthbrooding, with decreases occurring between egg pickup and hatching of the embryo (Day 6 of mouthbrooding). The pattern of change in concentrations of VTG in surface mucus of male parents differed from the pattern in plasma, with peak concentrations occurring at the time of hatching. The amount of VTG in mucus was similar to that measured in the female Oreochromis mossambicus during mouthbrooding of embryos. The appearance of peak VTG levels in the mucus at the time of hatching when plasma levels have declined and the availability of comparable amounts of mucus VTG in both maternal and paternal mouthbrooding tilapia, despite unequivalent plasma levels, support the possibility that parental provisioning of the young occurs during mouthbrooding in tilapia.

Animals↗

PubMed2000

Mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces: Cichlidae): the presence of eggs reduces androgen and estradiol levels during paternal and maternal parental behavior.

The black-chinned tilapia (Sarotherodon melanotheron) is considered a paternal mouthbrooder in which the male churns the eggs in his mouth for 14-18 days after they are fertilized. We previously showed that plasma androgen and estradiol concentrations increased significantly between the beginning and end of mouthbrooding. Here we provide evidence that androgen and estradiol are relatively high in prespawning male tilapia, decrease significantly with the initiation of mouthbrooding, and return to and slightly surpass prespawning levels by the end of mouthbrooding. We then test the hypothesis that the initiation of mouthbrooding causes a decrease in androgen and estradiol. We raised single pairs of tilapia in seawater aquaria and conducted two experiments. In the first, we removed eggs from males on the morning of Day 1 of mouthbrooding, followed changes in plasma androgen and estradiol in the afternoon of Day 1 and on Days 6, 11, and 16, and compared them to levels in control males who kept their eggs. Removing eggs from mouthbrooding males on the morning of Day 1 eliminated the decrease in plasma androgen and estradiol observed in the afternoon of Day 1 of mouthbrooding. This demonstrates that the eggs are necessary for the decrease. We observed that, infrequently, the female of the pair would pick up the eggs to brood them in her mouth. In a second experiment, in the afternoon of Day 1, we sampled both the male and female of pairs in which the female brooded eggs. In female-brooding pairs, the females had significantly lower androgen and estradiol levels than prespawning females. The black-chinned tilapia in captivity exhibits both paternal and maternal parental behavior. In both sexes the initiation of mouthbrooding triggers a decrease in androgen and estradiol concentrations. We conclude that the presence of eggs inhibits the pituitary-gonadal axis in both males and females and hypothesize that a chemical signal from the eggs is delaying the initiation of the next brood.

Androgens↗

PubMed1999

Infectious necrotizing enteritis and mortality caused by Vibrio carchariae in summer flounder Paralichthys dentatus during intensive culture.

An epizootic causing mortality among cultured summer flounder Paralichthys dentatus occurred in summer of 1998 at a land-based facility on Narragansett Bay, Rhode Island, USA. The disease, flounder infectious necrotizing enteritis (FINE), was characterized by reddening around the anal area, distended abdomens filled with opaque serosanguineous fluid, enteritis and necrosis of the posterior intestine. In extreme cases of the disease, the posterior intestine was detached from the anus and was observed coming out the vent. The intestine of individuals that recovered from the disease ended in a blind-sac; the abdomens of these fish were distended, due to food and water inside the intestinal blind-sac. A bacterium was isolated from ascites fluid and kidney of moribund flounder and identified as the causative agent in challenge experiments. The pathogen was identified as Vibrio carchariae by morphological and biochemical characteristics and sequence of the 16S rRNA. The LD50 estimate was 5 x 10(5) colony-forming units injected intraperitoneally into 100 to 200 g summer flounder.

Abdomen↗

PubMed1999

Metamorphosis in the summer flounder, Paralichthys dentatus: thyroidal status influences salinity tolerance.

Metamorphosis in the summer flounder (Paralichthys dentatus) is controlled by thyroid hormones (TH) and takes place as the larvae move from a salinity of about 35 parts per thousand (ppt) in the ocean to salinity ranging from 0-35 ppt in estuaries. Historically, the role of TH in juvenile and adult teleost osmoregulation has been ambiguous, and it is not known if TH influences larval teleost osmoregulatory development. This study addresses the influence of thyroxine (T4) on the development of tolerance to low (5 ppt) and high salinity (45 and 50 ppt) as determined by salinity tolerance tests. In untreated larvae, tolerance to both low and high salinity was high during early premetamorphosis (early pre-M) and decreased or was very low from late prometamorphosis (late pro-M) through mid-metamorphic climax (mid-MC). Salinity tolerance increased 2-3-fold during late MC when whole-animal T4 levels are highest, and reached maximum tolerance at the juvenile stage. The early induction of metamorphosis by exposing larvae in pre-M to exogenous T4 reduced tolerance to low salinity during early and mid-MC, though tolerance of fish that had developed into juveniles was not impaired. In contrast, T4 increased high salinity tolerance during early and mid-MC, and the juvenile stage. This T4-induced heterochrony in salinity tolerance with regards to developmental stage suggests that the effects of T4 on salinity tolerance may be uncoupled from accelerated metamorphosis. Treatment of larvae with thiourea (TU, an inhibitor of T4 synthesis) inhibited metamorphosis and reduced tolerance to high salinity, but did not affect tolerance to low salinity. Reduced tolerance to high salinity by TU was only partially counteracted by T4 treatment, suggesting that TU also affects hypoosmoregulatory activity by an extrathyroidal mechanism. Our findings suggest that in the summer flounder T4 plays a more important role in the development of hypoosmoregulatory ability than hyperosmoregulatory ability. J. Exp. Zool. 284:414-424, 1999.

Adaptation, Physiological↗

PubMed1998

Metamorphosis in the summer flounder (Paralichthys dentatus): stage-specific developmental response to altered thyroid status.

The summer flounder (Paralichthys dentatus) undergoes a true metamorphosis during which the bilaterally symmetrical larva transforms into an asymmetrical juvenile. This study addresses the influence of manipulating thyroid status on larval development and growth. Development was assessed by categorizing larvae in stages based on the position of the translocating eye and growth was assessed as a change in total length. Larvae were raised in seawater or in seawater containing thyroxine-sodium salt (100 ppb, T4) or thiourea (30 ppm, TU). Ambient T4 raised whole-animal T4 concentration almost threefold, whereas treatment with TU reduced whole-animal T4 concentration by 95%. The whole-animal T4 concentrations of untreated larvae increased during metamorphic climax (MC) and were related to developmental stage rather than age. Altering thyroid status of larvae in different stages had different consequences. T4 treatment of late premetamorphic (late pre-M) larvae accelerated their rate of development to prometamorphosis (pro-M), early MC, and mid MC, whereas TU treatment at this stage caused developmental stasis in early MC. T4 treatment of pro-M larvae accelerated development to early MC only and, unlike the response of late pre-M larvae, some of the pro-M larvae treated with TU slowly developed to late MC. TU treatment could inhibit completion of metamorphosis in early MC and mid MC, but not in late MC. Thyroid status of larvae had no effect on growth. However, starting at an age when most untreated and T4-treated larvae were in late MC, they began to grow longer than TU-treated larvae in developmental stasis at early MC and mid MC. Thus, T4 is necessary and sufficient for metamorphosis in summer flounder and, at this single dose, has a more pronounced effect on development at earlier stages.

Aging↗

PubMed1998

Intestinal uptake of lipovitellin from brine shrimp (Artemia franciscana) by larval inland silversides (Menidia beryllina) and striped bass (Morone saxatilis).

Intestinal uptake of lipovitellin (LV) from brine shrimp (Artemia franciscana) in larval inland silversides (Menidia beryllina) and striped bass (Morone saxatilis) was described using immunocytochemistry. Polyclonal antisera were raised against two subunits of LV (LV68 and LV190). When tested by immunocytochemistry, anti-LV68 showed cross-reactivity with some of the pancreatic cells especially in inland silversides. Therefore anti-LV190 was used to localize immunoreactive LV. Inland silversides at 14 days after hatching were fed Artemia nauplii and then sampled 4, 8, 12 hr after feeding. Similar experiments were carried out by using striped bass at 5 days and 15 days of age. They were sampled at 2, 4, 8, and 12 hr after feeding. Anterior enterocytes showed no evidence of uptake; however, the brush border of the cells of inland silversides reacted with the antiserum. Posterior enterocytes took up the LV and/or, possibly, their immunoreactive breakdown products. The pattern of uptake included accumulation in supranuclear vacuoles and digestion in supranuclear vacuoles, as suggested by the decay of the immunoreactivity over time. Thus, the posterior intestine of these larval fishes is the site of uptake and digestion of LV, an important nutritive component in the food of many larval fishes; this supports earlier findings using non-nutritive marker proteins.

Animals↗

PubMed1995

Cortisol mediates the increase in intestinal fluid absorption in Atlantic salmon during parr-smolt transformation.

We have previously shown in Atlantic salmon that the rate of fluid absorption by the posterior intestine (Jv) is elevated during the smolt stage in spring as a preadaptive development for osmoregulation in seawater. In the present study, we examined developmental differences in the responsiveness of Jv to cortisol and the corticosteroid antagonist, RU 486, through the parr-smolt transformation. Freshwater, juvenile salmon were administered slow-release implants of cortisol (50 micrograms/g body wt), RU 486 (1 mg/g body wt), or the implant without steroid (controls) at seven times from November 1992 through June 1993. Seven and 8 days after implantation, plasma cortisol concentrations and in vitro Jv were measured. In control salmon, both plasma cortisol and Jv peaked in April and were positively correlated over time. Cortisol implants stimulated Jv of salmon only during the parr and postsmolt stages, when Jv of controls was low. The exogenous cortisol was sufficient to stimulate Jv to a rate comparable to that measured for control salmon in the smolt stage. Conversely, RU 486 implants inhibited Jv only during the peak smolt period, when Jv of controls was elevated. Taken together, these results demonstrate that cortisol is a necessary and sufficient endocrine signal mediating this developmental change in intestinal function during parr-smolt transformation. This is the first report of plasma cortisol levels measured in fish treated with RU 486. Plasma cortisol was elevated by RU 486, suggesting that this corticosteroid antagonist blocked feedback inhibition on the pituitary-interrenal axis.

Animals↗

PubMed1994

Growth hormone- and prolactin-producing cells in the pituitary gland of striped bass (Morone saxatilis): immunocytochemical characterization at different life stages.

The striped bass (Morone saxatilis) is a seasonally breeding, long-lived, anadromous fish of growing economic importance. To describe the apparent activities of growth hormone (GH)- and prolactin (PRL)-producing cells, pituitaries were collected from captive juveniles and from wild adult fish in late spring off the Rhode Island coast during their coastal migration and in the Hudson River during the spawning migration. GH and PRL were separated by reversed-phase HPLC of pituitary extracts from captive adults and characterized as having apparent molecular masses of 23 kDa (GH) and 26 kDa (PRL) by SDS-polyacrylamide gel electrophoresis. Antisera generated in rabbits against synthetic fragments of GH and PRL188 from tilapia were shown by Western blot analysis of reversed-phase HPLC-purified striped bass GH and PRL and of striped bass pituitary extract to be specific for the appropriate hormone and were used to localize GH and PRL cells. GH cells and PRL cells lie in the proximal pars distalis and the rostral pars distalis, respectively. Small clusters of GH- and PRL-immunoreactive cells were found at ectopic sites within the pituitary. There were many intensely labeled GH cells in the pituitaries of juvenile and adult striped bass, whereas the immunoreactivity of GH cells in the pituitaries of spawning fish decreased. PRL cells in juvenile fish kept in fresh water had big, round-nuclei, and were heavily labeled, indicating that they were active. PRL cells in adult fish from seawater were also intensely labeled, but had kidney-shaped nuclei, indicating inactivity. PRL cells in fish from the spawning ground had polymorphic nuclei, appearing as round, indented or kidney-shaped forms, and they were unevenly and lightly labeled, suggesting highly variable stages of activity. No difference was found between males and females. The apparent activities of GH- and PRL-producing cells differ among these life stages, suggesting changing roles for the hormones.

Animals↗

PubMed1993

Immunocytochemical and immunogold localization of two prolactin isoforms in the same pituitary cells and in the same granules in the tilapia (Oreochromis mossambicus).

The tilapia pituitary secretes two forms of prolactin (tPRL) and a single growth hormone (tGH). The tPRLs share only 69% sequence identity and are designated tPRL177 and tPRL188 to indicate the number of amino acid residues in each isoform. Our aim was to develop specific antisera for detection of these three related polypeptides. Ten peptides corresponding to unique epitopes on the tPRLs and two peptides of tGH were synthesized using solid-phase methods, conjugated to carrier proteins, and used as immunogens for antibody production in rabbits. Select antisera for the tPRLs were highly specific, exhibiting only 1% cross-reactivity to the alternate tPRL under noncompetitive ELISA conditions at dilutions used in immunocytochemical analysis. The anti-tGH specifically bound to cells in the proximal pars distalis. Production of both tPRLs by a single cell type was indicated by the binding of both anti-tPRL177 and anti-tPRL188 to the same cells in the rostral pars distalis. Ultrastructural analysis of PRL-producing cells stained sequentially using the two different anti-tPRL antibodies labeled with immunogold of two size classes indicated that both tPRLs appear in the same granules. These findings suggest that the biological significance of two forms of PRL in the adult tilapia is not a function of differential regulation of two different classes of PRL cells or differential release of unique secretory granules.

Amino Acid Sequence↗

PubMed1992

In vitro effects of homologous prolactins on testosterone production by testes of tilapia (Oreochromis mossambicus).

The tilapia, Oreochromis mossambicus, produces two prolactins designated tPRL177 and tPRL188 to indicate the number of amino acid residues in each. The direct in vitro actions of tPRL177 and tPRL188 on basal and ovine luteinizing hormone (LH)-induced testosterone production in minced testes of courting and noncourting (bachelor) tilapia were examined. Courting males were housed with females and were used as soon as they built a spawning pit; noncourting males were housed with other males and were used when they appeared female-like in coloration. The in vitro culture system consisted of two phases. In phase 1 (0-10 hr), testicular tissue was incubated without (control) or with the tPRLs--both alone and together and in doses ranging from 0.5 to 32 microM. In phase 2 (10-16 hr), the culture medium was replaced with medium containing 6.25 microM (0.25 micrograms/ml) ovine LH. Testosterone production during both phases was determined by radioimmunoassay of the medium. The tPRLs stimulated testosterone production during phase 1 in courting males (by 25%) but not in noncourting males. Exposure to either or both tPRLs in phase 1 enhanced the response of testicular tissue from courting males to ovine LH (by 10%) and inhibited the response of minced testes taken from noncourting males (by 12%). This is the first evidence to demonstrate direct gonadal activity of homologous PRL in a teleost.

Animals↗

PubMed1992

Induction by beta-estradiol of vitellogenin in striped bass (Morone saxatilis): characterization and quantification in plasma and mucus.

Striped bass (Morone saxatilis) were implanted with beta-estradiol to induce the production of vitellogenin, the egg yolk precursor produced by the liver. Electrophoretic analysis revealed that beta-estradiol caused marked production of a plasma protein of apparent molecular mass 170 kDa. Size exclusion chromatography suggested that the estradiol-induced protein circulated as a dimer. This protein was purified from the plasma of estradiol-treated fish by DEAE-agarose column chromatography and used to induce antibodies in rabbits and goats. Western blots revealed that the antiserum bound to the putative vitellogenin in plasma from estradiol-treated fish and adult females, but not with any proteins in male plasma. Western blot of ovarian extract revealed several smaller immunoreactive protein bands and supported the identity of the purified protein as vitellogenin. A competitive ELISA was developed with sensitivity in a range from 8 to 1000 ng/ml. Plasma concentrations of adult females during their spawning migration ranged from 100 to 600 micrograms/ml. Western blot of mucus extract revealed the presence of a 170-kDa protein in vitellogenic female fish along with several minor bands ranging from 50 to 110 kDa. Positive immunoreactivity was present in the surface mucus of all females and in none of the males collected during a spawning migration in the Hudson River.

Animals↗

PubMed1992

Asynchrony of changes in tissue and plasma thyroid hormones during the parr-smolt transformation of coho salmon.

The relationship between plasma thyroid hormone concentrations and the thyroid hormone concentrations in selected tissues was examined throughout the spring during the typical course of parr-smolt transformation in coho salmon (Oncorhynchus kisutch) in fresh water and also in coho salmon moved prematurely to seawater. The thyroid hormones thyroxine (T4) and triiodothyronine (T3) were extracted from brain, liver, and muscle tissue. The T4 and T3 concentrations in the extracts and plasma were measured by radioimmunoassay. The peak in plasma T4 occurred in late April; however, the concentration of T4 in the brain and liver increased before levels of T4 in plasma increased. During the rise in plasma T4, the T4 content in muscle decreased. Plasma T3 concentrations were unchanged in March and April, but decreased in May. Transfer to seawater eliminated the late April peak in plasma T4 levels, indicating suppressed thyroid activity; however, the tissues of salmon in seawater contained more T3 than tissues of salmon in fresh water at this time. These findings indicate complex peripheral regulation of thyroidal status in this teleost and represent the first bridge between compartmental models of thyroid hormone kinetics and actual measurement of tissue pools of thyroid hormones in an ectothermic vertebrate. In summary, tissue concentrations of thyroid hormones did not echo plasma concentrations, indicating that thyroidal status cannot be inferred from plasma data alone.

Aging↗

PubMed1991

Amino acid sequence of growth hormone isolated from medium of incubated pituitary glands of tilapia (Oreochromis mossambicus).

The amino acid sequence of tilapia (Oreochromis mossambicus) growth hormone (GH) was determined directly by Edman degradation of peptide fragments generated by lysyl endopeptidase and trypsin digestion. The N-terminal residue was deduced to be pyroglutamic acid through the use of pyroglutamyl aminopeptidase; its removal allowed amino acid sequence determination of the remainder of the N-terminal trypsin peptide by Edman degradation. Tilapia GH is composed of 187 amino acid residues and shows high similarity to other perciform GHs. Sequence identities are: 89% with tuna GH, 83% with bonito GH, 85% with yellowtail GH, 89% with red sea bream GH, and 34% with bovine GH. The two asparagine residues (Asn-148 and Asn-184) were recovered by Edman degradation, suggesting the absence of N-glycosylation.

Amino Acid Sequence↗

PubMed1991

In vitro effects of arginine vasotocin on testosterone production by testes of rainbow trout (Oncorhynchus mykiss).

The objective of this study was to investigate the effect of arginine vasotocin (AVT) on testosterone (T2) production by the rainbow trout testis in culture. AVT increased T2 production in a dose-dependent manner in immature testes. The maximum response (10 nM AVT) increased T2 production 6-fold over basal (3-6 pg/mg tissue protein). Mature testes did not respond to AVT. Salmon gonadotropin (2.5 nM sGtH, SGA-GtH) stimulated T2 production by both juvenile (5-fold) and mature (11-fold) testes. When AVT (100 nM) was added in addition to salmon gonadotropin (sGtH; from 0.1 to 100 nM), AVT had a stimulatory effect at the submaximal doses of sGtH, but T2 production did not exceed the maximum level obtained with sGtH (100 nM) alone. Isotocin also increased T2 production although to a lesser degree than AVT. The maximum response at 10 nM increased T2 production 4-fold over basal. beta-Endorphin had no effect on T2 production.

Animals↗

PubMed1988

Complete amino acid sequences of a pair of fish (tilapia) prolactins, tPRL177 and tPRL188.

The complete amino acid sequences of a pair of tilapia (Oreochromis mossambicus) prolactins (PRLs) were determined. The larger PRL of molecular mass 20,836 Da consists of 188 amino acid residues. The smaller PRL of molecular mass 19,584 Da is 11 residues shorter. On alignment of the two sequences, the 19.6-kDa PRL (tPRL177) has two conspicuous deletions on the NH2-terminal side of the disulfide bond which connects the first and second cysteine residues. The degree of similarity between the two PRL sequences is unexpectedly low (130 identical residues, 69%) compared with that between the variants of other teleostean PRLs. Circular dichroism spectra and hydropathy profiles suggest structural similarity of the two PRLs. The sequence of the 20.8-kDa PRL (tPRL188) has 69% identity with that of salmon PRL. The sequence of tPRL177 is 56% identical with that of salmon PRL. Each tilapia PRL is equally similar to mammalian PRLs (about 30% identical residues). Regions highly conserved among teleostean and mammalian PRLs were identified on the COOH-terminal side of the disulfide bond connecting the first and second cysteine residues.

Amino Acid Sequence↗