Jude Fitzgibbon

Spectral tuning and molecular evolution of rod visual pigments in the species flock of cottoid fish in Lake Baikal

Lake Baikal in Eastern Siberia is the deepest and one of the largest and most ancient lakes in the world. However, even in the deepest regions, oxygenation levels do not fall below 75-80% of the surface levels. This has enabled a remarkable flock of largely endemic teleost fish of the sub-order Cottoidei to colonize all depth habitats. We have previously shown that species that occupy progressively deeper habitats show a blue shift in the peak wavelength of absorbance (lambda max) of both their rod and cone visual pigments; for the rod pigments, a number of stepwise shifts occur from about 516 nm in littoral species to about 484 nm in abyssal species. By sequencing the rod opsin gene from 11 species of Baikal cottoids that include representatives from all depth habitats, we have been able to identify four amino acid substitutions that would account for these shifts. The effect of each substitution on lambda max is approximately additive and each corresponds to a particular lineage of evolution.

The rhodopsin-encoding gene of bony fish lacks introns

A study of the sequences of the rhodopsin-encoding genes (Rh) in eight fish species from two of the major subdivisions of the teleosts reveals that no introns are present in the coding region. This contrasts with the opsin-encoding genes of all other vertebrates where either four or five introns are invariably found. Phylogenetic analysis shows that this intronless teleost Rh is homologous to the intron-containing Rh of amphibia, birds and mammals. Possible mechanisms for intron loss are discussed, including replacement by homologous conversion of Rh with a processed cDNA.

Mapping of RXRB to human chromosome 6p21. 3

Retinoid X Receptor beta (RXRB) is a member of the retinoid X receptor (RXR) family of nuclear receptors which are involved in mediating the effects of retinoic acid (RA). We have confirmed the localization of RXRB to chromosome 6 and we have mapped the gene to chromosome 6p21. 3‐p21.1 by PCR amplification of 5′ untranslated sequence in panels of rodent‐human somatic cell hybrids and to 6p21.3 by fluorescent in situ hybridization.

Human guanylate kinase (GUK1): cDNA sequence, expression and chromosomal localisation

Guanylate kinase (GK) catalyses the conversion of GMP to GTP as part of the cGMP cycle. In mammalian phototransduction, this cycle is essential for the regeneration of cGMP following its hydrolysis by phosphodiesterase. Mutations in different parts of this signalling cascade lead to retinal degeneration in humans. Protein studies have localized a locus for GK to a region of human chromosome 1 that also contains an autosomal recessive form of retinitis pigmentosa (RP12) and Ushers type 11a (USH2A). We report the sequence of this human GK (GUK1) and a further refinement of its localization to 1q32‐41, placing it in the same interval as USH2A.

Localisation of the human blue cone pigment gene to chromosome band 7q31.3-32

Blue cone pigment (BCP) is one of three types of cone photoreceptors responsible for normal colour vision. In this study, the BCP gene has been localised to chromosome 7q31.3-32 by fluorescent in situ hybridisation of cosmid clones containing the gene. This is consistent with previous mapping of the BCP gene to chromosome 7q31-35.

Chromosomal localization of three mouse diacylglycerol kinase (DAGK) genes: genes sharing sequence homology to the Drosophila retinal degeneration A (rdgA) gene ☆

There is growing evidence to support some form of light-activated phosphoinositide signal transduction pathway in the mammalian retina. Although this pathway plays no obvious role in mammalian phototransduction, mutations in this pathway cause retinal degenerations in Drosophila. These include the retinal degeneration A mutant, which is caused by an alteration in an eye-specific diacylglycerol kinase (DAGK) gene. In our efforts to consider genes mutated in Drosophila as candidates for mammalian eye disease, we have initially determined the map position of three DAGK genes in the mouse.

Localization of the gene encoding human phosphatidylinositol transfer protein (PITPN) to 17p13.3: a gene showing homology to the Drosophila retinal degeneration B gene (rdgB).

The human gene for phosphatidylinositol transfer protein (PITPN) has previously been shown to share sequence and functional homology to part of the Drosophila retinal degeneration B gene (rdgB). In view of the possible involvement of the PITPN locus in the etiology of retinal disease, the gene has been mapped to human chromosome 17p13.3 and mouse Chromosome 11.

Localisation of the gene encoding diacylglycerol kinase 3 (DAGK3) to human chromosome 3q27-28 and mouse chromosome 16

The gene encoding a 90 kDa diacylglycerol kinase protein, DAGK3, that is predominately expressed in the retina, was localised by fluorescence in situ hybridisation to human chromosome 3q27-28. This was subsequently confirmed by mapping of its mouse homologue to chromosome 16, a region syntenic to this part of human chromosome 3. No retinopathies have so far been assigned to this region.