Larval development of silver sea bream (Sparus sarba): ontogeny of RNA-DNA ratio, GH, IGF-I, and Na(+)-K(+)-ATPase.

To ascertain some of the important biochemical and molecular events that take place during early larval development of silver sea bream (Sparus sarba), we undertook a study of changes in the morphology as well as the ontogeny of the RNA-DNA ratio, growth hormone (GH), insulin-like growth factor I (IGF-I) messenger RNA abundance, Na(+)-K(+)-ATPase subunit mRNA abundance, and Na(+)-K(+)-ATPase enzyme activity. Larvae samples were collected at 1 to 46 days posthatch (dph). At 7 dph the yolk sac was fully absorbed, and from 28 dph onward larvae underwent rapid developmental changes to the juvenile stage. The RNA-DNA ratio was highest at 1 dph, decreased to low levels between 7 and 21 dph, then increased by 28 dph, and then again by 46 dph. The ontogenetic profiles of GH, IGF-I, and Na(+)-K(+)-ATPase alpha1 and beta1 subunits were studied using reverse transcriptase polymerase chain reaction, coupled with radioisotope hybridization of immobilized DNA. Growth hormone abundance reached a constant and high level from 35 dph onward, whereas the IGF-I level reached a peak at 35 dph and then significantly decreased. Both Na(+)-K(+)-ATPase alpha1 and beta1 subunit mRNAs increased up to 35 dph, however, at 46 dph the alpha1 subunit remained high whereas the beta1 subunit decreased. Na(+)-K(+)-ATPase activity was low in 1-dph larvae but increased rapidly as development progressed. The importance of these findings is discussed within the context of larval development.

Gonadotropin-releasing hormone content in the brain and pituitary of male and female grass rockfish (Sebastes rastrelliger) in relation to seasonal changes in reproductive status.

The involvement of individual molecular forms of GnRH in the regulation of reproductive cyclicity in a viviparous marine teleost, the grass rockfish (Sebastes rastrelliger), was evaluated by relating the brain and pituitary content of the neuropeptide to reproductive status. The presence of sea bream (sb) GnRH, chicken GnRH-II, and salmon GnRH in the brain was confirmed by their elution pattern on HPLC and RIA. In addition, HPLC elution profiles suggest that there may be a fourth form of GnRH. All forms of GnRH were found in male and female brains in all reproductive conditions. However, only sbGnRH could be detected in appreciable amounts in the pituitary. Of the four forms of GnRH found in the rockfish, only sbGnRH fluctuated during the reproductive cycle and large accumulations were detected in the brains and pituitaries of postspawn females and regressed males. The accumulation of sbGnRH at the end of the reproductive cycle is suggested to reflect a decline in GnRH secretion relative to synthesis. The dominance of sbGnRH in the pituitary and its individual fluctuation in relation to seasonal changes in reproductive status suggests that sbGnRH is an important regulator of gonadotropin-mediated reproductive activity in rockfish.

Molecular forms of GnRH in three model fishes: rockfish, medaka and zebrafish.

Three species of fish have become important in the study of reproduction and development. Rockfish are a model for developmental studies of live-bearing perch-like fish, whereas medaka and zebrafish are models for developmental and genetic studies. The forms of GnRH are identified in the brains of each of these fish and in the pituitary of the rockfish to investigate the role of GnRH in reproduction. Here, we report that grass rockfish (Sebastes rastrelliger) have three forms of GnRH in brain extracts as determined by HPLC elution position and RIA. These forms are identified as sea bream GnRH, chicken GnRH-II and salmon GnRH. In contrast, only two forms of GnRH were detected in brain extracts of medaka (Oryzias latipes) and zebrafish (Brachydanio rerio): salmon GnRH and chicken GnRH-II. Rockfish is distinct from medaka and zebrafish in that the most abundant form of GnRH in the rockfish pituitary is sea bream GnRH, whereas this form is absent in the other two fishes. The identification of sea bream GnRH in the rockfish brain and pituitary extracts indicates that the phylogenetic emergence of sea bream GnRH is earlier than the order Perciformes.

Maturation of the hypothalamo-pituitary-gonadal axis of male Syrian hamsters.

Light-microscope immunocytochemistry (ICC) was used to investigate postnatal changes in the morphology of LHRH neurons in the brains of male Syrian hamsters and to relate these changes to more overt maturational developments within the hypothalamo-pituitary-gonadal axis. The animals were maintained under long-day photoperiods (14L:10D), and groups of 6-7 were killed at 10-day intervals from Day 15 to Day 65. Their brains were fixed with 4% paraformaldehyde, sectioned sagittally with a vibratome (75 microns), and processed for ICC using monoclonal LHRH antibody HU4H. Throughout the study period, the hamsters showed a progressive increase in plasma gonadotropin levels, closely followed by an increase in testicular weight and plasma testosterone levels. Histology of the testes revealed that spermatogenesis was already qualitatively completed by Day 35 and quantitative aspects were established by Day 45. Within the brain, LHRH neuronal perikarya were distributed primarily in the medial septal-preoptic area and the diagonal band of Broca; morphologically, these immunopositive neurons were either monopolar or bipolar. The total number of LHRH neurons detected in the areas examined was approximately 440 throughout the developmental period, and the relative proportions of monopolar and bipolar subtypes (86% and 14%, respectively) remained unchanged. In contrast, the area of the perikarya, as determined by autoimage analysis, showed a highly significant age-related increase, both for the monopolar and bipolar neurons. It is suggested that these developmental changes in the LHRH neurons reflect an increase in LHRH synthesis and may, therefore, provide a neuroendocrine trigger for the onset of puberty.

Tumor markers and screening tools in cancer detection.

The ideal cancer screening tool would be one that is sufficiently sensitive to detect early malignancy, specific to only cancer and not a host of other conditions, specific for the type of cancer, specific for the location of the cancer, commensurate to the tumor bulk, cost-effective, easy to use, safe, acceptable to the general population, and acceptable to the medical community. No one laboratory test or radiograph meets all of the preceding criteria. Great strides have been made, however, in the early diagnosis of cancer. For example, breast cancer is being diagnosed at much earlier stages because of mammography. Just a few years ago, safety was a major issue because of the high level of radiation exposure connected with mammography. Today, radiation exposure is minimal, and the benefits far outweigh the potential harm. Research must continue to perfect the existing screening tools and develop new tools that will enable the early detection of malignant disease.

A quantitative assessment of the gametogenic and androgenic properties of testicular steroids in hypophysectomized rats.

The ability of testicular steroids to maintain the quantitative aspects of spermatogenesis was compared with reference to their androgenic properties. Hypophysectomized rats were injected daily with 0.2 mg progesterone, 20 alpha-dihydroprogesterone, 3 beta-hydroxy-5 alpha-pregnan-20-one, testosterone or testosterone propionate for 30 days beginning 2 days after the operation. Testosterone propionate was the most potent steroid tested both in terms of its peripheral androgenic effects and its ability to prevent the post-operative decline in the weight of the testis and seminiferous tubules and the numbers of germ cells throughout their differentiation. The natural androgen, testosterone, exhibited weak gametogenic properties and only partly maintained the normal measures of spermatogenesis. Progesterone exhibited low intrinsic androgenic potency yet was significantly more effective than testosterone in maintaining spermatogenesis; it prevented the degeneration of spermatocytes during the later stages of meiotic prophase and the reduction divisions resulting in an increased yield of step 7 spermatids. Low androgenic and gametogenic properties were exhibited by 20 alpha-dihydroprogesterone and 3 beta-hydroxy-5 alpha-pregnan-20-one. These results may indicate that testosterone produced locally in the seminiferous tubules from progesterone is more effective in maintaining spermatogenesis than androgens entering from the circulation. Alternatively, progesterone may act more directly on the germ cells than previously envisaged.

Specific chemical dissociation of fibrillar and non-fibrillar components of amyloid deposits.

In systemic amyloidosis, a fatal disorder for which there is no effective treatment, the extracellular protein deposits are composed of amyloid fibrils together with a non-fibrillar glycoprotein, amyloid P component (AP). Methyl 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranoside (MO beta DG), a recently identified ligand for AP, was tested for its ability to produce in-vitro elution of AP which had been laid down with amyloid fibrils in vivo. Millimolar concentrations of MO beta DG completely dissociated AP from human and murine splenic amyloid deposits. Availability of this material thus provides for the first time the opportunity for specific molecular dissection of amyloid deposits. If MO beta DG or a related substance were effective in vivo it might be of therapeutic importance.