Goutam Karan

Two Cell Lineages, myf5 and myf5-Independent, Participate in Mouse Skeletal Myogenesis

In skeletal muscle development, the myogenic regulatory factors myf5 and myoD play redundant roles in the specification and maintenance of myoblasts, whereas myf6 has a downstream role in differentiating myocytes and myofibers. It is not clear whether the redundancy between myf5 and myoD is within the same cell lineage or between distinct lineages. Using lineage tracing and conditional cell ablation in mice, we demonstrate the existence of two distinct lineages in myogenesis: a myf5 lineage and a myf5-independent lineage. Ablating the myf5 lineage is compatible with myogenesis sustained by myf5-independent, myoD-expressing myoblasts, whereas ablation of the myf6 lineage leads to an absence of all differentiated myofibers, although early myogenesis appears to be unaffected. We also demonstrate here the existence of a significant myf5 lineage within ribs that has an important role in rib development, suggested by severe rib defects upon ablating the myf5 lineage.

Recurrent 17 bp duplication in PITX3 is primarily associated with posterior polar cataract (CPP4)

The human lens is a unique tissue continually evolving and ever increasing in size primarily formulated by placement of newly differentiated fibre cells in concentric lamellae. This is analogous to an onion skin arrangement. This differentiation triggers loss of both nucleus and other cell organelles. Furthermore, the main factors for maintaining lens clarity are the tight and ordered mutual binding of the fibre cells and the packing of their intracellular building blocks termed crystallins. It is known that lens transparency is a crucial trade-off between the concentration of these macromolecules and their hydration. Disruption of normal levels of hydration can lead to opacity. Cataract, opacification of the eye lens, is the commonest cause of blindness in the world. During infancy and early childhood it frequently results in visual impairment or blindness. In children, it can cause an irreversible amblyopia. Nearly half of all congenital cataracts are normally characterised as familial and they are perceived to be a key feature if not the predominant feature of about 200 genetic diseases.1–3 Recent research has paved the way for a better understanding of the underlying mechanisms of inherited forms of cataract. Inherited cataract is clinically heterogeneous, and, thus far, more than 14 distinct loci in humans have been identified, for 11 phenotypically distinct forms of autosomal dominant congenital cataracts (ADCC).4,5 Progress has been made in elucidating cataract causing mutations in human genes encoding the transparent intracellular lens proteins (crystallins), membrane gap junction proteins (connexins), water channel proteins (aquaporins), developmental transcription factors FOXE3 ,6 EYA1,7 PAX6 ,8 MAF ,9 and PITX3. 10 Based on this insight, it can be deduced that cataracts exhibit marked phenotypic and genotypic heterogeneity. Here we report a number of interesting findings about the PITX3 gene: (1) we have found mutations in …

Elovl4 haploinsufficiency does not induce early onset retinal degeneration in mice

ELOVL4 was first identified as a disease-causing gene in Stargardt macular dystrophy (STGD3, MIM 600110.) To date, three ELOVL4 mutations have been identified, all of which result in truncated proteins which induce autosomal dominant juvenile macular degenerations. Based on sequence homology, ELOVL4 is thought to be another member within a family of proteins functioning in the elongation of long chain fatty acids. However, the normal function of ELOVL4 is unclear. We generated Elovl4 knockout mice to determine if Elovl4 loss affects retinal development or function. Here we show that Elovl4 knockout mice, while perinatal lethal, exhibit normal retinal development prior to death at day of birth. Further, postnatal retinal development in Elovl4 heterozygous mice appears normal. Therefore haploinsufficiency for wildtype ELOVL4 in autosomal dominant macular degeneration likely does not contribute to juvenile macular degeneration in STGD3 patients. We found, however, that Elovl4+/- mice exhibit enhanced ERG scotopic and photopic a and b waves relative to wildtype Elovl4+/+ mice suggesting that reduced Elovl4 levels may impact retinal electrophysiological responses.

A novel RDS/peripherin gene mutation associated with diverse macular phenotypes.

Pattern dystrophy is a heterogeneous group of retinal dystrophies of which butterfly-shaped pattern dystrophy (BPD) and adult-onset foveomacular dystrophy (AOFMD) are the two most common forms. BPD is characterized by a butterfly-shaped, irregular, depigmented lesion at the level of the retinal pigment epithelium. In contrast, AOFMD is characterized by the presence of slightly elevated, symmetric, solitary, round to oval, yellow lesions at the level of the retinal pigment epithelium. We identified three independent kindreds with pattern dystrophy, one with four patients affected with BPD and the other two with 14 affected patients with AOFMD. We performed complete ophthalmic examination, fluorescein angiography, linkage mapping, and mutational screening in the RDS/peripheringene in the affected patients. Patients affected with BPD had a best-corrected vision of 20/20 to 20/25, whereas vision in the eyes of patients with AOFMD ranged from 20/20 to 20/400. In all three kindreds, sequence analysis identified an A-to-G change at nucleotide position 422 of the RDS/peripheringene, predicting a novel Tyr-141-Cys substitution. A haplotype analysis revealed that these three kindreds shared an identical disease haplotype at the RDS/peripherinlocus, indicating that the mutation reflects a founder effect. The sequence change that segregated with the disease phenotype was not observed in 200 control chromosomes. Our results identified a novel mutation in the RDS/peripheringene that can cause diverse macular phenotypes. Genetic and clinical investigation of pattern dystrophy may provide useful diagnostic tools and new treatment strategies for this disorder.

Treatment with carbonic anhydrase inhibitors depresses electroretinogram responsiveness in mice.

We showed that a functional complex of CA4 and Na+/bicarbonate co-transporter (NBC1) is specifically expressed in the choriocapillaris and that mutations in CA4 disrupt NBC1-mediated HCO3 −- transport leading to acidification of the retina. This finding (Yang et al., 2005) point to the importance of a functional CA4 for the survival of photoreceptors and imply that CA inhibitors may have long-term adverse effects on vision.

Fundus Appearance of Choroideremia Using Optical Coherence Tomograpy

Choroideremia is an X-linked recessive disorder characterized by progressive degeneration of the choroid, RPE and retina Goedblood et al., 1942). Patients initially present with night blindness in the first or second decade that progresses to severe constriction of the visual field. Central acuity is lost late in life (Kril et al.).

Choroidal Neovascularization in Patients with Adult-Onset Foveomacular Dystrophy Caused by Mutations in the RDS/Peripherin Gene

Adult-onset foveomacular dystrophy (AOFMD) was first described as a peculiar foveomacular dystrophy in 1974 (Gass, 1974). A mutation in the RDS/peripherin gene (Pro-210- Arg) was identified in this particular kindred (Gorin et al., 1994). Subsequently, Feist and coworkers reported a case of choroidal neovascularization associated with AOFMD in a patient with the Pro-210-Arg mutation (Feist et al., 1994). To our knowledge, CNV in AOFMD is rare as demonstrated by only two other descriptions of it in the literature: 1) Vine and Schatz described three instances in two patients, neither of whom had an identi- fied mutation (Vine et al., 1980); and 2) Battaglia Parodi and coworkers described a case of subfoveal CNV in a vascularized pigment epithelial detachment in a patient with AOFMD (Battaglia et al., 2000). Recently, an A to G change, predicting a Tyr-141-Cys substitution in the RDS/peripherin gene has been described that results in AOFMD which is dominantly transmitted (Yang et al., 2004). In addition, a frameshift mutation in exon 1 of the RDS/peripherin gene, that results in a guanine deletion at nucleotide position 112, leads to a premature termination of the gene product at amino acid 38 and has been implicated in the genesis of AOFMD in a 13-family member kindred (Yang et al., 2003). We present three cases of subfoveal CNV in patients with AOFMD, which were caused by RDS/peripherin gene mutations.