Biomedical subjects

J Hodin

Publications and source records attributed to J Hodin.

7 recordsLinked to original sources

PubMed2000

Plasticity and constraints in development and evolution.

Morphological similarities between organisms may be due to either homology or homoplasy. Homologous structures arise by common descent from an ancestral form, whereas homoplasious structures are independently derived in the respective lineages. The finding that similar ontogenetic mechanisms underlie the production of the similar structures in both lineages is not sufficient evidence of homology, as such similarities may also be due to parallel evolution. Parallelisms are a class of homoplasy in which the two lineages have come up with the same solution independently using the same ontogenetic mechanism. The other main class of homoplasy, convergence, is superficial similarity in morphological structures in which the underlying ontogenetic mechanisms are distinct. I argue that instances of convergence and parallelism are more common than is generally realized. Convergence suggests flexibility in underlying ontogenetic mechanisms and may be indicative of developmental processes subject to phenotypic plasticity. Parallelisms, on the other hand, may characterize developmental processes subject to constraints. Distinguishing between homology, parallelisms and convergence may clarify broader taxonomic patterns in morphological evolution.

Animals↗

PubMed2000

Parallel alterations in the timing of ovarian ecdysone receptor and ultraspiracle expression characterize the independent evolution of larval reproduction in two species of gall midges (Diptera: Cecidomyiidae).

Although most insects reproduce in the adult stage, facultative larval or pupal reproduction (paedogenesis) has evolved at least six times independently in insects, twice in gall midges of the family Cecidomyiidae (Diptera). Paedogenesis in gall midges involves the precocious growth and differentiation of the ovary in an otherwise larval form. We have previously shown that the timing of expression of the Ecdysone Receptor (EcR) and Ultraspiracle (USP), the two proteins that constitute the functional receptor for the steroid hormone 20-hydroxyecdysone, regulates the timing and progression of ovarian differentiation in Drosophila melanogaster (Diptera: Drosophilidae). Here we test the hypothesis that precocious activation of EcR and USP in the ovaries of paedogenetic gall midges allows for precocious ovarian differentiation. Using monoclonal antibodies directed against insect EcR and USP proteins, we first show that when these gall midges are reared under conditions that promote typical, metamorphic development, up- regulation of EcR and USP occurs in the final larval stage. By contrast, in the paedogenetic life cycle, EcR and USP are up-regulated early in the first larval stage. A similar pattern is seen for two independently-evolved paedogenetic gall midges, Heteropeza pygmaea and Mycophila speyeri. We discuss our results in the context of developmental constraints on the evolution of paedogenesis in dipteran insects.

Animals↗

PubMed2000

Different mechanisms underlie phenotypic plasticity and interspecific variation for a reproductive character in drosophilids (Insecta: Diptera).

The insect ovary is a modular structure, the functional unit of which is the ovariole. Ovariole number is positively correlated with potential reproductive output. Among drosophilids (Insecta: Diptera), ovariole number shows both phenotypic plasticity and substantial interspecific and interpopulational variation. Here we examine the mechanistic connection between phenotypic plasticity and genetically fixed variation in ovariole number within the melanogaster species group. When a laboratory population of Drosophila melanogaster was reared under reduced food conditions, differences in ovariole number were entirely due to alterations in cell differentiation during the wandering stage at the very end of larval development. Cell growth and cell death were not affected. When these same flies were reared under a variety of temperatures, ovariole number differences arose during the latter half of the third (final) larval instar. Cell differentiation was affected, although cell number was not, and ovariole number differences were established before metamorphosis. In contrast, genetically fixed, interspecific and interpopulational variability in ovariole number was caused by alterations in the dynamics of cell differentiation and by cell number differences. Furthermore, the stages affected were different in different species and populations in the melanogaster species group, ranging from the first (D. sechellia) through the middle of the third (D. simulans and D. mauritiana) larval stage. Therefore, the mechanistic bases for plasticity-based variability are largely distinct from the mechanistic bases for interspecific and interpopulational variability. Our results suggest that phenotypic plasticity indicates evolutionary flexibility in underlying ontogenetic processes.

Animals↗

PubMed1998

The ecdysone receptor and ultraspiracle regulate the timing and progression of ovarian morphogenesis during Drosophila metamorphosis.

Ecdysteroids regulate insect metamorphosis through the edysone receptor complex, a heterodimeric nuclear receptor consisting of the ecdysone receptor (EcR) and its partner ultraspiracle (USP). Differentiation in the Drosophila ovary at metamorphosis correlates with colocalization of USP and the EcR-A isoform in all but one of eight mesoderm-derived somatic cell types. The one exception is the larval terminal filament (TF) cells, in which only USP is detectable during cell differentiation. In cells destined to form the basal stalks and anterior oviduct, USP colocalizes with what appears to be the EcR-B2 isoform. Flies heterozygous for a deletion of the EcR gene exhibit several defects in ovarian morphogenesis, including a heterochronic delay in the onset of terminal filament differentiation. Flies heterozygous for a strong usp allele exhibit accelerated TF differentiation. Flies simultaneously heterozygous for both EcR and usp have additional phenotypes, including several heterochronic shifts, delayed initiation and completion of terminal filament morphogenesis and delayed ovarian differentiation during the first day of metamorphosis. Terminal filament morphogenesis is severely disrupted in homozygous usp clones. Our results demonstrate that proper expression of the ecdysone receptor complex is required to maintain the normal progression and timing of the events of ovarian differentiation in Drosophila. These findings are discussed in the context of a developmental and evolutionary role for the ecdysone receptor complex in regulating the timing of ovarian differentiation in dipteran insects.

Animals↗

PubMed1996

A retinaldehyde dehydrogenase as a structural protein in a mammalian eye lens. Gene recruitment of eta-crystallin.

eta-Crystallin is a taxon-specific crystallin, a major component of the eye lens in elephant shrews (Macroscelidea). Sequence analysis of eta-crystallin from two genera of elephant shrews and expression of recombinant eta-crystallin show that the protein is a cytoplasmic (class 1) aldehyde dehydrogenase (ALDH1, EC 1.2.1.3) with activity for the oxidation of retinaldehyde to retinoic acid. Unlike many other mammals, elephant shrews have two ALDH1 genes. One encodes ALDH1/eta-crystallin which, in addition to its very high expression in lens, is also the predominant form of ALDH1 expressed in other parts of the eye. The second gene encodes a "non-lens" ALDH1 (ALDH1-nl) which is the predominant form expressed in liver. This pattern of tissue preference contrasts with other mammals which make use of the same major ALDH1 transcript in both ocular and non-ocular tissues. Thus the gene recruitment of ALDH1/eta-crystallin as a structural protein in elephant shrew lenses is associated with its collateral recruitment as the major form of ALDH1 expressed in other parts of the eye.

Aldehyde Oxidoreductases↗

PubMed1993

A macrophage migration inhibitory factor is expressed in the differentiating cells of the eye lens.

A discrete 10-kDa polypeptide (10K) is expressed from early stages in the embryonic chicken lens. Since this has potential as a marker for lens cell development, chicken 10K and its homologues from mouse and human lenses were identified by protein sequencing and cloning. Surprisingly, lens 10K proteins appear to be identical to a lymphokine, macrophage migration inhibitory factor (MIF), originally identified in activated human T cells. Using microdissection and PCR techniques, we find that expression of 10K/MIF is strongly correlated with cell differentiation in the developing chicken lens. Northern blot analysis shows that 10K/MIF is widely expressed in mouse tissues. These results suggest that proteins with MIF activity may have roles beyond the immune system, perhaps as intercellular messengers or part of the machinery of differentiation itself. Indeed, partial sequence of other small lens proteins identifies another MIF-related protein (MRP8) in calf lens. The relatively abundant expression of MIF in lens may have clinical significance, with the possibility of involvement in ocular inflammations that may follow damage to the lens.

Amino Acid Sequence↗

PubMed1993

5'-RACE PCR of mRNA for three taxon-specific crystallins: for each gene one promoter controls both lens and non-lens expression.

Gene recruitment of enzyme crystallins is a novel process in molecular evolution in which genes for some metabolic enzymes acquire extremely high expression in lens without prior gene duplication. Using the RACE method, the 5' end of the mRNAs for duck lens delta 1-, argininosuccinate lyase/delta 2- and lactate dehydrogenase-B/epsilon-crystallin has been amplified from lens and non-lens tissues and sequenced. In all three cases the major transcription start sites were identical in lens and in other tissues. This suggests that for these three genes, and in contrast to at least one other example, gene recruitment does not require the presence of alternative tissue-preferred promoters.

Animals↗