Two Independent Functions of Collier/Early B Cell Factor in the Control of Drosophila Blood Cell Homeostasis.

Justine Oyallon,Michèle Crozatier,Alain Vincent,Joanna Krzemień,Ismaël Morin-Poulard,Nathalie Vanzo,Kenneth Söderhäll

doi:10.1371/journal.pone.0148978

Abstract

Blood cell production in the Drosophila hematopoietic organ, the lymph gland, is controlled by intrinsic factors and extrinsic signals. Initial analysis of Collier/Early B Cell Factor function in the lymph gland revealed the role of the Posterior Signaling Center (PSC) in mounting a dedicated cellular immune response to wasp parasitism. Further, premature blood cell differentiation when PSC specification or signaling was impaired, led to assigning the PSC a role equivalent to the vertebrate hematopoietic niche. We report here that Collier is expressed in a core population of lymph gland progenitors and cell autonomously maintains this population. The PSC contributes to lymph gland homeostasis by regulating blood cell differentiation, rather than by maintaining core progenitors. In addition to PSC signaling, switching off Collier expression in progenitors is required for efficient immune response to parasitism. Our data show that two independent sites of Collier/Early B Cell Factor expression, hematopoietic progenitors and the PSC, achieve control of hematopoiesis.

Highlights

Understanding how the balance between progenitor cell maintenance and differentiation is regulated in developing and adult tissues is a major area of investigation
Low levels of col expression in lymph gland anterior lobes define a submedullar zone In wild type second larval instar lymph glands, both in situ hybridization and immunostaining indicated that all cells of the anterior lobes express low levels of col (Fig 1A, 1E and 1E’), in addition to high levels in the Posterior Signaling Center (PSC) and stochastic expression in the secondary lobes [10]
In mid third instar larval lymph gland, col expression in the medullary zone overlaps with the expression domain of the thioester-containing protein 4 (Fig 1F and 1F’) [36], which marks a sub-set of hemocyte progenitors in the medullary zone (Fig 1G and 1G’)

Summary

Introduction

Understanding how the balance between progenitor cell maintenance and differentiation is regulated in developing and adult tissues is a major area of investigation. Two types of blood cells (called hemocytes) differentiate in the lymph gland, the plasmatocytes endowed with phagocytic. Dual Role of Collier in Drosophila Hematopoiesis activity, and crystal cells required for melanisation. They are released into the circulation, the hemolymph, upon lymph gland dispersal at the onset of metamorphosis [8, 9]. If the larva falls prey to wasp parasitism (i.e. wasps lay eggs in Drosophila larvae), a third hemocyte type, the lamellocytes, massively differentiate at the expense of progenitor maintenance, provoking lymph gland dispersal before metamorphosis [8, 10, 11]. Lamellocytes released into the hemolymph contribute to encapsulation and neutralisation of parasitoid wasp eggs [8, 12]

Methods

Results

Conclusion