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Remembering Marguerite Vogt: The ring gland


By Davy Jones, University of Kentucky, Reprinted by permission.


Marguerite Vogt's first scientific contributions were in the field of Drosophila development. At the moment of her entry (in 1940) into this field of developmental endocrinology, various competing theories were hotly contested concerning the source and action of hormones that controlled the remarkable developmental process of insect metamorphosis. Also at this time, the comparable field in vertebrate research had reached a need for new approaches to build upon what classical endocrine techniques had elucidated. Further intersecting with the above was the newly appreciated recognition of the power offered by genetical approaches with Drosophila (i.e., recent Nobel Prize to the Drosophila geneticist Thomas Hunt Morgan). Astutely, Dr. Vogt delved with a passion into elucidating the necessary endocrine understanding of Drosophila metamorphosis, to which the power of Drosophila genetics could then be applied.

The experimental focus of Dr. Vogt's experiments was to determine the endocrine source of hormonal signals that regulate the metamorphic replacement of larval body parts with the adult body parts that develop from incipient cellular masses known as imaginal discs. It was Dr. Vogt who first demonstrated that in higher fly development, a hormone released by the lateral parts of a "ring gland" both (1) promotes early proliferative growth of imaginal discs, and (2) acts at the onset of metamorphosis to trigger adult differentiation of those imaginal discs (1942-1943; eye-antennal imaginal disc).

Initial confusion had also developed in the field as to the mixed cellular composition of this endocrine ring gland, and as to which cells were responsible for various endocrine activities at different times in the higher fly life cycle. It was Dr. Vogt who first histologically tracked that cells which comprise the adult endocrine glands known as the "corpora allata" have their origin in a group of cells in the center of the larval ring gland that (she demonstrated) are also endocrinologically active during larval development (1941-1942). This advance enabled the field to gain its solid footing in confidently focusing on the correct Drosophila cells to investigate for a hypothesized "juvenile hormone," that was postulated to be involved in the metamorphic developmental decision of all insects.

Toward that end, Dr. Vogt made the extremely important endocrine discovery that a product of these central cells of the young larval ring gland can exert an activity similar to the gonadotropic activity exerted by a product of the adult female corpora allata. Her work established thereby a gonadotropic biological assay for endocrine activity of various aged 'larval corpora allatal' cells of the ring gland (1943). Indeed, with this bioassay she provided the first developmental analysis of the endocrine activity of the corpora allatal cells of the larval ring gland. This assay was subsequently used by the field for the next two decades as the primary assay for endocrine productivity of larval corpora allatal cells of dipteran ring glands, until the field finally developed the chemical means identify glandular products secreted in vitro culture. Conversely, she also showed that the adult corpora allata, when implanted into Drosophila larvae, secrete a product that inhibits metamorphic production of adult cuticle (1946). This result established a second bioassay that is still the primary assay used by the field today to detect juvenilizing activity of synthetic juvenoids on higher Diptera.

Live photographs of two ring glands of Day 5 hour 21 old larvae from Drosophila hydei. On the left is a whole ring gland, on the right the two lateral "thigh ends" (S = "schenkelzellen") freed from upper "broad arch" region that contains the corpora allatal cells (between the arrows) . C. c =.Corpora cardia. Adapted from Fig. 51 on page 436 of Vogt (1943).

The above experiments had demonstrated that the larval corpora allata secrete a product that can exert an adult gonadotropic activity, and that the adult corpora allata secret a product that can exert an effect to prevent adult differentiation of the immature cuticle. However, there remained the burning issue of whether in higher Diptera the larval corpora allata exert an endocrine activity that maintains the larval (juvenile) state. Dr. Vogt then applied her microsurgical skills and sharp experimental methods to using the Drosophila system to test this controversial hypothesis. Indeed, she provided the field its confirmation of such an endocrine activity from the Drosophila larval ring gland, when she microsurgically evidenced that the corpora allatal portion of the gland (see figure below) exerts an activity to delay the differentiation of the eye-antennal imaginal disc (1943). Hence, the Drosophila system, with its powerful genetics, was established by Dr. Vogt to be a viable model system with which to probe the most fundamental questions in how hormones regulate development and differentiation in insects generally.

In short, today's advanced research field on the metamorphic endocrinology of Drosophila owes its successful start over six decades ago to Dr. Vogt. Her experimental discoveries in this area in the early 1940s established the identity of the corpora allatal region of the larval ring gland, evidenced its endocrine activity in both young and mature larvae, and demonstrated that the genetic model organism, Drosophila, is also a viable model for elucidating fundamental endocrine mechanisms controlling growth and differentiation of insects.

Live photographs of two ring glands of Day 5 hour 21 old larvae from Drosophila hydei. On the left is a whole ring gland, on the right the two lateral "thigh ends" (S = "schenkelzellen") freed from upper "broad arch" region that contains the corpora allatal cells (between the arrows) . C. c =.Corpora cardia. Adapted from Fig. 51 on page 436 of Vogt (1943).