Serpent, Suppressor of Hairless and U-shaped are crucial regulators of hedgehog niche expression and prohemocyte maintenance during Drosophila larval hematopoiesis

Abstract

SUMMARYThe lymph gland is a specialized organ for hematopoiesis, utilized during larval development in Drosophila. This tissue is composed of distinct cellular domains populated by blood cell progenitors (the medullary zone), niche cells that regulate the choice between progenitor quiescence and hemocyte differentiation [the posterior signaling center (PSC)], and mature blood cells of distinct lineages (the cortical zone). Cells of the PSC express the Hedgehog (Hh) signaling molecule, which instructs cells within the neighboring medullary zone to maintain a hematopoietic precursor state while preventing hemocyte differentiation. As a means to understand the regulatory mechanisms controlling Hh production, we characterized a PSC-active transcriptional enhancer that drives hh expression in supportive niche cells. Our findings indicate that a combination of positive and negative transcriptional inputs program the precise PSC expression of the instructive Hh signal. The GATA factor Serpent (Srp) is essential for hh activation in niche cells, whereas the Suppressor of Hairless [Su(H)] and U-shaped (Ush) transcriptional regulators prevent hh expression in blood cell progenitors and differentiated hemocytes. Furthermore, Srp function is required for the proper differentiation of niche cells. Phenotypic analyses also indicated that the normal activity of all three transcriptional regulators is essential for maintaining the progenitor population and preventing premature hemocyte differentiation. Together, these studies provide mechanistic insights into hh transcriptional regulation in hematopoietic progenitor niche cells, and demonstrate the requirement of the Srp, Su(H) and Ush proteins in the control of niche cell differentiation and blood cell precursor maintenance.

The EBF transcription factor Collier directly promotes Drosophila blood cell progenitor maintenance independently of the niche

“…S6). However, consistent with previous findings (11,21), Antp mutant larvae lacked a PSC as revealed by Col and Antp immunostaining (Fig. 4E and Fig.…”

“…Thus, we suggest that the PSC does not function as a niche required for blood cell progenitor maintenance. Several lines of evidence supporting the niche function of the PSC are based on ectopic or overexpression of various proteins in the PSC to alter its size and activity (11,13,15,17,21,29). These manipulations may not always reflect the real function of the PSC as they can cause sustained activation of abnormal programs that indirectly impinge on prohemocytes.…”

“…Col and Antp are required for PSC formation during late embryonic development and col as well as Antp mutant are devoid of PSC (10)(11)(12)21). Moreover, all progenitors differentiate into crystal cells and plasmatocytes in col mutant LG (10,11), and an increase in crystal cell differentiation was reported in Antp 17 /Antp 25 mutant LG (11).…”

Crustacean hematopoiesis

“…Normally, two different hemocyte lineages are detected in the CZ: CCs and plasmatocytes. The GATA transcription factor Serpent (Srp) is crucial for the development of all types of hemocytes and is highly important for niche cell differentiation and control (Lebestky et al, 2000;Tokusumi et al, 2010). Downstream of Srp, the transcription factor Glial cell missing (Gcm) is required for the differentiation of the plasmatocyte lineage, whereas the RUNX-like transcription factor Lozenge (Lz) directs prohemocytes into CCs (Lebestky et al, 2000).…”

Germ line differentiation factor Bag of Marbles is a regulator of hematopoietic progenitor maintenance during Drosophila hematopoiesis

“…TepIVGal4 (Avet-Rochex et al, 2010;Tokusumi et al, 2010) was obtained from the Drosophila Genetic Resource Center in Kyoto, Japan. The UAS-bam RNAi strains 10422R-1 and 10422R-2 were obtained from the National Institute of Genetics in Mishima, Japan; HMS00029 was obtained from Harvard Medical School.…”