Biomedical subjects

Bruce A Adams

Publications and source records attributed to Bruce A Adams.

7 recordsLinked to original sources

PubMed2006

Role of two genes encoding PACAP in early brain development in zebrafish.

To study the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in early brain development, we examined PACAP and its receptors for first expression and then separately knocked down the two forms of PACAP in zebrafish where development is rapid and observable. We injected morpholinos (antisense oligonucleotides) into fertilized eggs to block PACAP. Morphological changes in the brain were observed in embryos at 27 h post fertilization (hpf). Using in situ hybridization of early brain marker genes, we found that the most striking effects were an increase in pax2.1 expression in eye stalks associated with absence of either form of PACAP or an increase in eng2 and fgf8 in the midbrain-hindbrain boundary after loss of PACAP2. These marker genes are among the earliest factors in the formation of the midbrain-hindbrain boundary, an early organizing center. We suggest that PACAP is a target gene with feedback inhibition on pax2.1, eng2, or fgf8 in specific brain areas. In the hindbrain, the absence of either form of PACAP had little effect, as shown by expression of ephA4 and meis1.1. During midbrain development, our evidence suggests that PACAP1 can activate mbx. In both the diencephalon and/or forebrain, lack of PACAP1 or PACAP2 led to an increase in fgf8, again suggesting a suppressive effect of PACAP during development on these important genes that help to define cells in the forebrain. The early expression of transcripts for PACAP and its receptors by 0.5-6 hpf make both PACAP1 and PACAP2 candidates for factors that influence brain development.

Animals↗

PubMed2004

Contaminant effects on the teleost fish thyroid.

Numerous environmentally relevant chemicals, including polychlorinated hydrocarbons, polycyclic aromatic hydrocarbons, organochlorine pesticides, chlorinated paraffins, organophosphorous pesticides, carbamate pesticides, cyanide compounds, methyl bromide, phenols, ammonia, metals, acid loads, sex steroids, and pharmaceuticals, exert acute or chronic effects on the thyroid cascade in the approximately 40 teleost fish species tested to date. Thyroid endpoints, therefore, serve as biomarkers of exposure to environmental pollutants. However, the mechanisms underlying thyroid changes and their physiological consequences are poorly understood because the thyroid cascade may respond indirectly and it has considerable capacity to compensate for abuses that otherwise would disrupt thyroid hormone homeostasis. Indeed, a xenobiotic-induced change in fish thyroid function has yet to be conclusively causally linked to decreased fitness or survival. Other complications in interpretation arise from the diversity of test conditions employed and the often indiscriminate use of numerous thyroid endpoints. Future work should be directed toward standardizing test conditions and thyroid endpoints and investigating causal links between thyroid changes and fish growth, reproduction, and development. Development may be particularly susceptible to thyroid disruption, and thyroid endpoints appropriate for early life stages need to be applied.

Animals↗

PubMed2003

Cloning and localization of three forms of gonadotropin-releasing hormone, including the novel whitefish form, in a salmonid, Coregonus clupeaformis.

Cells containing different GnRH peptides currently are thought to have distinct locations and functions in the brain. Lake whitefish is the first salmonid species to have three forms of GnRH peptide in contrast to later-evolving salmonids (salmon and trout) in which only two forms have been identified. Our objective was to isolate the cDNAs that code for these transcripts and to localize the transcripts for the three forms of GnRH in adult lake whitefish brain. Also, we provide phylogenetic analysis of these three whitefish genes based on their preprohormone sequence. From whitefish we isolated cDNAs encoding chicken (c)GnRH-II, salmon (s)GnRH, and the novel whitefish (wf)GnRH. The three cDNAs each encode only one GnRH and are placed in separate groups with phylogenetic analysis. A combination of in situ hybridization and immunocytochemistry with two antisera revealed neurons that expressed protein and/or mRNA for cGnRH-II in the midbrain and hindbrain; sGnRH in the olfactory nerve and bulb, ventral telencephalon, and preoptic area; and wfGnRH in the same latter two brain regions and the hypothalamus. Thus, in the anterior brain, cells containing sGnRH and wfGnRH were in the same brain areas but not at identical locations in the ventral telencephalon and preoptic area. Based on our results, we speculate that both sGnRH and wfGnRH have gonadotropin-releasing roles in the lake whitefish brain.

Amino Acid Sequence↗

PubMed2003

Six novel gonadotropin-releasing hormones are encoded as triplets on each of two genes in the protochordate, Ciona intestinalis.

GnRH is the key regulator of the reproductive axis in vertebrates, but little is known about GnRH before the origin of vertebrates. We have identified two genes encoding GnRH in a protochordate, Ciona intestinalis, thought to be related to the ancestral animal that gave rise to vertebrates. Each gene, Ci-gnrh1 and Ci-gnrh2, encodes in tandem three GnRH peptides, each of which is unique compared with known forms. Ci-gnrh1 encodes three peptides and contains no introns, whereas Ci-gnrh2 encodes three more peptides but has two introns. This is the first report in which more than one GnRH peptide is encoded on a single gene. The Ciona genes reveal consensus promoter elements that are conserved compared with human GNRH1. Both tunicate genes are expressed as mRNA early and throughout development, measured at the stages of four-cell, gastrulation, tail release, and tail resorption. In a closely related tunicate species, Ciona savignyi, we used in silico analysis to identify two similar genes encoding six peptides, only one of which is unique compared with C. intestinalis. Immunohistochemistry showed that at least one GnRH peptide was in the nerve net that surrounds the dorsal strand. Synthetic forms of the seven novel tunicate peptides induced release of gametes in adult tunicates. In contrast, the peptides did not activate the human GnRH-I receptor or cause release of LH in a rat pituitary cell assay. These data provide insight into the structural evolution of the GnRH peptides and their genes and show a functional role for GnRH in tunicate spawning.

Aging↗

PubMed2002

Pituitary adenylate cyclase-activating polypeptide and growth hormone-releasing hormone-like peptide in sturgeon, whitefish, grayling, flounder and halibut: cDNA sequence, exon skipping and evolution.

To better understand the evolution of pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH), we isolated the cDNAs encoding these peptides from the brains of five species of fish: sturgeon, whitefish, grayling, flounder and halibut. Both hormones are encoded in tandem in full-length cDNAs. We compared the phylogenetic relationship among these and other known sequences encoding PACAP. In closely related species, transcripts encoding PACAP and GHRH are strongly conserved in the hormone coding regions, moderately conserved in the signal peptide, cryptic peptide and 3'-untranslated regions, but are most varied in the 5'-untranslated regions.Next, we compared the deduced amino acid sequences for the peptides to known sequences. Sturgeon and whitefish have a PACAP(38) peptide sequence that is 92% conserved compared to human PACAP(38), the highest for a fish reported to date. GHRH is the lesser conserved of the two peptides with only 39% to 45% conservation between fish and human.Each of the five fish species had a second cDNA encoding a short precursor lacking GHRH(1-32), the bioactive portion of GHRH. This suggests that exon skipping in GHRH-PACAP transcripts may be an important mechanism for regulating the ratio of PACAP to GHRH peptides.

Alternative Splicing↗

PubMed2002

Transcription and translation of the salmon gonadotropin-releasing hormone genes in brain and gonads of sexually maturing rainbow trout (Oncorhynchus mykiss).

Rainbow trout sexually mature at the end of Year 3. The form of GnRH that controls gonadotropin release in trout is salmon GnRH (sGnRH). In the tetraploid rainbow trout, two genes encode an identical sGnRH peptide. The sGnRH gene-1 produces one mRNA, whereas sGnRH gene-2 can produce more than one. This study asks whether the transcripts and their protein products are expressed in the brain and gonads and whether the pattern correlates with sexual maturity over the final year leading to first spawning. Brain sGnRH mRNA and protein were continuously present throughout the third year. We show for the first time that the long sGnRH-2 mRNA transcript is expressed in neural tissue and not exclusively in gonadal tissue. Expression of the long sGnRH-2 mRNA in the brain coincides with high levels of sGnRH peptide in the brain during a time of increased gonadal growth. Thus, the long sGnRH-2 mRNA in the brain may act to regulate sGnRH production in a stage-specific rather than a tissue-specific manner. In gonads, local sGnRH is thought to play an autocrine/paracrine role in regulating gonadal maturation and spawning. In the maturing gonads, sGnRH gene-1 and -2 are expressed intermittently. Strikingly, sGnRH peptide was not detected in the gonads at any time during Year 3. These results suggest that either the sGnRH transcripts in the gonads are not translated into protein or, if translated, the protein is rapidly released, resulting in gonadal content below 1 fM per fish.

Alternative Splicing↗

PubMed2002

Three forms of gonadotropin-releasing hormone, including a novel form, in a basal salmonid, Coregonus clupeaformis.

Multiple forms of GnRH within individual brains may have different functions. However, some vertebrates such as salmonids continue to reproduce even though they have lost or do not express 1 of the 3 forms of GnRH found in most other teleosts. We examined a basal salmonid, lake whitefish, to determine the mechanism by which a reduction in the number of GnRH forms occurs. We identified for the first time 3 distinct GnRHs in a salmonid. One form is novel and is designated whitefish GnRH. The primary structure is pGlu-His-Trp-Ser-Tyr-Gly-Met-Asn-Pro-Gly-NH(2). HPLC and RIA were used for purification followed by Edman degradation for sequence determination. Mass spectroscopy was used to confirm the sequence and amidation of the peptide. The other 2 forms, salmon GnRH and chicken GnRH-II, are identical to the 2 forms found in salmon, which evolved later than whitefish. Synthetic whitefish GnRH is biologically active, as it increased mRNA expression of growth hormone and the alpha-subunit for LH and thyroid-stimulating hormone in dispersed fish pituitary cells. Our data support the hypothesis that the ancestral salmonid had a third GnRH form when the genome doubled (tetraploidization), but the third form was lost later in some salmonids due to chromosomal rearrangements. We suggest that the salmon GnRH form compensated for the loss of the third form.

Animals↗