Segmentation gene

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Segmentation genes of Drosophila embryo Segmentation genes of Drosophila embryo.png
Segmentation genes of Drosophila embryo

A segmentation gene is a gene involved in the early developmental stages of pattern formation. It regulates how cells are organized and defines repeated units in the embryo. Segmentation genes have been documented in three taxa: arthropods (i.e. insects and crabs), [2] chordates (i.e. mammals and fish), and annelids (i.e. leeches and earthworms). [3] [4] In Drosophila melanogaster , a common fruit fly, segmentation genes divide the embryo into 14 parasegments [5] which are among the first compartments to form within the embryo. [6] Rare variants in segmentation genes can cause changes in appearance of differing severity depending on its type. The genes can be classified into 3 groups: Gap genes, Pair-rule genes and Segment polarity genes. [7]

Contents

Gap genes

Gap genes are among the first genes expressed in the embryo. Here, expression refers to the translation of the gene. Gap genes were named as such because loss-of-function variants in gap genes resulted in large deletions (or gaps) in the neighbouring segments of the embryo. [8] The expression of gap genes is regulated by maternally deposited factors called maternal effect genes. Maternal effect genes encode factors like messenger RNA needed for early development such as cell division. [9] One of their main roles is to provide polarity and sense of direction to the embryo: which region will become the anterior or the head region, and which region will become the posterior or the tail region. [7]   For instance, the mRNA of bicoid, a maternal affect gene, is transported to the anterior region of the embryo and then spreads toward the posterior region. [10] This creates a concentration gradient where bicoid expression is highest in the anterior and gradually decreases towards the posterior. [10] Bicoid along with other maternal effect genes like nanos create multiple concentration gradients that regulate the expression of gap genes. [7] Gap genes are expressed in large sections of the embryo multiple parasegments wide. Kruppel, for instance, is expressed in parasegments 4-6. [11] There are at least 6 types [12] of gap genes but the three [13] that are well-known are hunchback, [14] knirps, and kruppel .

Different concentration gradients of gap genes establish parasegment boundaries. [15] These parasegment boundaries help regulate or control the expression of pair-rule genes as well as segment polarity genes. [16] Lastly, the gap genes also play a role in later development such as giving rise to neurons along with formation of muscles and the gut. [15]

Pair-rule genes

Pair-rule genes are genes that are expressed in alternating parasegments of the embryo for a total of 7-8 parasegments. [17] The boundaries of parasegments are not determined by grooves that can be seen on the embryo but are compartments that show gene expression. One parasegment is made from the back half of a visible segment (not parasegment) and the front half of the visible segment behind it. [18] An expression of a pair-rule gene in one parasegment is followed by a region of no expression in the following parasegment. [19] For example, odd-skipped genes are expressed in alternating even-numbered parasegments (stripe 2, 4, and so on) while even-skipped genes are expressed in odd-numbered parasegments (stripe 1, 3, and so on). [20] They were termed as such because loss-of-function variants in even-skipped genes can cause the disappearance of odd-numbered parasegments only leaving behind the even-numbered parasegments, hence, the name. [21] Lastly, the pair-rule genes regulate the expression of segment polarity genes. [22]

Segment polarity genes

Segment polarity genes are expressed in distinct regions within a parasegment. A parsegment is divided into anterior - the head -region, and the posterior - the tail - region. [23] One segment polarity gene, engrailed, is expressed in the anterior part of each parasegment while another, wingless , is expressed in the posterior region. [24] Loss-of-function variants in engrailed, for instance, can result in defects within the anterior portions of each parasegment. Lastly, certain segment polarity genes like wingless are involved in the planning and development of body parts such as the wings. [25] [26]

Related Research Articles

<i>Drosophila</i> embryogenesis Embryogenesis of the fruit fly Drosophila, a popular model system

Drosophila embryogenesis, the process by which Drosophila embryos form, is a favorite model system for genetics and developmental biology. The study of its embryogenesis unlocked the century-long puzzle of how development was controlled, creating the field of evolutionary developmental biology. The small size, short generation time, and large brood size make it ideal for genetic studies. Transparent embryos facilitate developmental studies. Drosophila melanogaster was introduced into the field of genetic experiments by Thomas Hunt Morgan in 1909.

Segmentation in biology is the division of some animal and plant body plans into a linear series of repetitive segments that may or may not be interconnected to each other. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida. These three groups form segments by using a "growth zone" to direct and define the segments. While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning. Even within these groups, different organisms have different mechanisms for segmenting the body. Segmentation of the body plan is important for allowing free movement and development of certain body parts. It also allows for regeneration in specific individuals.

<span class="mw-page-title-main">Morphogen</span> Biological substance that guides development by non-uniform distribution

A morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation, one of the core processes of developmental biology, establishing positions of the various specialized cell types within a tissue. More specifically, a morphogen is a signaling molecule that acts directly on cells to produce specific cellular responses depending on its local concentration.

Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment, and Hox genes in vertebrates specify the types and shape of vertebrae that will form. In segmented animals, Hox proteins thus confer segmental or positional identity, but do not form the actual segments themselves.

<i>Krüppel</i>

Krüppel is a gap gene in Drosophila melanogaster, located on the 2R chromosome, which encodes a zinc finger C2H2 transcription factor. Gap genes work together to establish the anterior-posterior segment patterning of the insect through regulation of the transcription factor encoding pair rule genes. These genes in turn regulate segment polarity genes. Krüppel means "cripple" in German, named for the crippled appearance of mutant larvae, who have failed to develop proper thoracic and anterior segments in the abdominal region. Mutants can also have abdominal mirror duplications.

<span class="mw-page-title-main">Gap gene</span> Gene used to develop body sections in embryos

A gap gene is a type of gene involved in the development of the segmented embryos of some arthropods. Gap genes are defined by the effect of a mutation in that gene, which causes the loss of contiguous body segments, resembling a gap in the normal body plan. Each gap gene, therefore, is necessary for the development of a section of the organism.

In the field of developmental biology, regional differentiation is the process by which different areas are identified in the development of the early embryo. The process by which the cells become specified differs between organisms.

<span class="mw-page-title-main">Pair-rule gene</span> Gene involved in the development of segmented embryos of insects

A pair-rule gene is a type of gene involved in the development of the segmented embryos of insects. Pair-rule genes are expressed as a result of differing concentrations of gap gene proteins, which encode transcription factors controlling pair-rule gene expression. Pair-rule genes are defined by the effect of a mutation in that gene, which causes the loss of the normal developmental pattern in alternating segments.

<i>engrailed</i> (gene) Protein family

engrailed is a homeodomain transcription factor involved in many aspects of multicellular development. First known for its role in arthropod embryological development, working in consort with the Hox genes, engrailed has been found to be important in other areas of development. It has been identified in many bilaterians, including the arthropods, vertebrates, echinoderms, molluscs, nematodes, brachiopods, and polychaetes. It acts as a "selector" gene, conferring a specific identity to defined areas of the body, and co-ordinating the expression of downstream genes.

<span class="mw-page-title-main">Zone of polarizing activity</span>

The zone of polarizing activity (ZPA) is an area of mesenchyme that contains signals which instruct the developing limb bud to form along the anterior/posterior axis. Limb bud is undifferentiated mesenchyme enclosed by an ectoderm covering. Eventually, the limb bud develops into bones, tendons, muscles and joints. Limb bud development relies not only on the ZPA, but also many different genes, signals, and a unique region of ectoderm called the apical ectodermal ridge (AER). Research by Saunders and Gasseling in 1948 identified the AER and its subsequent involvement in proximal distal outgrowth. Twenty years later, the same group did transplantation studies in chick limb bud and identified the ZPA. It wasn't until 1993 that Todt and Fallon showed that the AER and ZPA are dependent on each other.

Orthodenticle (otd) is a homeobox gene found in Drosophila that regulates the development of anterior patterning, with particular involvement in the central nervous system function and eye development. It is located on the X chromosome. The gene is an ortholog of the human OTX1/OTX2 gene.

<i>Bithorax</i> complex

The Bithorax complex (BX-C) is one of two Drosophila melanogaster homeotic gene complexes, located on the right arm of chromosome 3. It is responsible for the differentiation of the posterior two-thirds of the fly by the regulation of three genes within the complex: Ultrabithorax (Ubx), abdominal A (abd-A), and Abdominal B (Abd-B).

A segmentation gene is a generic term for a gene whose function is to specify tissue pattern in each repeated unit of a segmented organism. Animals are constructed of segments; however, Drosophila segments also contain subdivided compartments. There are five gene classes which each contribute to the segmentation and development of the embryonic drosophila. These five gene classes include the coordinate gene, gap gene, pair-rule gene, segment polarity gene, and homeotic gene. In embryonic drosophila, the pair-rule gene defines odd-skipped and even-skipped genes as parasegments, showing 7 stripes in the embryo. In the next gene class, segment polarity gene, individual segments each have their own anterior and posterior pole, resulting in 14 segments. In the fruit fly Drosophila melanogaster, segment polarity genes help to define the anterior and posterior polarities within each embryonic parasegment by regulating the transmission of signals via the Wnt signaling pathway and Hedgehog signaling pathway. Segment polarity genes are expressed in the embryo following expression of the gap genes and pair-rule genes. The most commonly cited examples of these genes are engrailed and gooseberry in Drosophila melanogaster. The segment polarity is the last step in embryonic development and a repeated pattern where each half of each segment is deleted and a mirror-image is duplicated and reversed to replace that half segment; thus, forming a pattern element.

Homeotic selector genes confer segment identity in Drosophila. They encode homeodomain proteins which interact with Hox and other homeotic genes to initiate segment-specific gene regulation. Homeodomain proteins are transcription factors that share a DNA-binding domain called the homeodomain. Changes in the expression and function of homeotic genes are responsible for the changes in the morphology of the limbs of arthropods as well as in the axial skeletons of vertebrates. Mutations in homeotic selector genes do not lead to elimination of a segment or pattern, but instead cause the segment to develop incorrectly.

<span class="mw-page-title-main">Germ-band extension</span> Morphogenic process during embryogenesis

Germ-band extension is a morphogenic process widely studied in the development of Drosophila melanogaster in which the germ-band, which develops into the segmented trunk of the embryo, approximately doubles in length along the anterior-posterior axis while subsequently narrowing along the dorsal-ventral axis.

Staufen is a protein product of a maternally expressed gene first identified in Drosophila melanogaster. The protein has been implicated in helping regulate genes important in determination of gradients that set up the anterior posterior axis such as bicoid and oskar. Staufen proteins, abbreviated Stau, are necessary for cell localization during the oogenesis and zygotic development. It is involved in targeting of the messenger RNA encoding these genes to the correct pole of the egg cell.

<i>Homeotic protein bicoid</i> Protein-coding gene in the species Drosophila melanogaster

Homeotic protein bicoid is encoded by the bcd maternal effect gene in Drosophilia. Homeotic protein bicoid concentration gradient patterns the anterior-posterior (A-P) axis during Drosophila embryogenesis. Bicoid was the first protein demonstrated to act as a morphogen. Although bicoid is important for the development of Drosophila and other higher dipterans, it is absent from most other insects, where its role is accomplished by other genes.

Evx1 is a mammalian gene located downstream of the HoxA cluster, which encodes for a homeobox transcription factor. Evx1 is a homolog of even-skipped (eve), which is a pair-rule gene that regulates body segmentation in Drosophila. The expression of Evx1 is developmentally regulated, displaying a biphasic expression pattern with peak expression in the primitive streak during gastrulation and in interneurons during neural development. Evx1 has been shown to regulate anterior-posterior patterning during gastrulation by acting as a downstream effector of the Wnt and BMP signalling pathways. It is also a critical regulator of interneuron identity.

The protocerebrum is the first segment of the panarthropod brain.

<span class="mw-page-title-main">Hunchback (gene)</span> Maternal effect gene and gap gene

Hunchback is a maternal effect and zygotic gene expressed in the embryos of the fruit fly Drosophila melanogaster. In maternal effect genes, the RNA or protein from the mother’s gene is deposited into the oocyte or embryo before the embryo can express its own zygotic genes.

References

  1. ↑ Schroeder, Mark D.; Pearce, Michael; Fak, John; Fan, HongQing; Unnerstall, Ulrich; Emberly, Eldon; Rajewsky, Nikolaus; Siggia, Eric D.; Gaul, Ulrike (2004-08-31). "Transcriptional Control in the Segmentation Gene Network of Drosophila". PLOS Biology. 2 (9): e271. doi: 10.1371/journal.pbio.0020271 . ISSN   1545-7885. PMC   514885 . PMID   15340490.
  2. ↑ "Arthropod - Exoskeleton, Segmented, Jointed | Britannica". www.britannica.com. 2024-10-25. Retrieved 2024-12-05.
  3. ↑ Deutsch, Jean S. (2004). "Segments and parasegments in Arthropods: a functional perspective". BioEssays. 26 (10): 1117–1125. doi:10.1002/bies.20111. ISSN   1521-1878. PMID   15382136.
  4. ↑ Balavoine, Guillaume (2014). "Segment formation in Annelids: patterns, processes and evolution". The International Journal of Developmental Biology. 58 (6–7–8): 469–483. doi:10.1387/ijdb.140148gb. ISSN   0214-6282. PMID   25690963.
  5. ↑ Clark, Erik; Akam, Michael (2016-08-15). Wittkopp, Patricia J (ed.). "Odd-paired controls frequency doubling in Drosophila segmentation by altering the pair-rule gene regulatory network". eLife. 5: e18215. doi: 10.7554/eLife.18215 . ISSN   2050-084X. PMC   5035143 . PMID   27525481.
  6. ↑ Hughes, Sarah C.; Krause, Henry M. (2001-04-01). "Establishment and maintenance of parasegmental compartments". Development. 128 (7): 1109–1118. doi:10.1242/dev.128.7.1109. hdl: 1807/16229 . ISSN   0950-1991. PMID   11245576.
  7. 1 2 3 Gilbert, Scott F. (2000), "The Origins of Anterior-Posterior Polarity", Developmental Biology. 6th edition, Sinauer Associates, retrieved 2024-12-04
  8. ↑ Patel, Nipam H.; Liu, Paul Z. (2009-01-01), "Chapter 231 - Segmentation", in Resh, Vincent H.; Cardé, Ring T. (eds.), Encyclopedia of Insects (Second Edition), San Diego: Academic Press, pp. 909–912, doi:10.1016/b978-0-12-374144-8.00240-x, ISBN   978-0-12-374144-8 , retrieved 2024-12-04
  9. ↑ Mitchell, Laura E. (2022-01-13). "Maternal effect genes: Update and review of evidence for a link with birth defects". Human Genetics and Genomics Advances. 3 (1). doi:10.1016/j.xhgg.2021.100067. ISSN   2666-2477. PMC   8756509 . PMID   35047854.
  10. 1 2 Stauber, Michael; Jäckle, Herbert; Schmidt-Ott, Urs (1999-03-30). "The anterior determinant bicoid of Drosophila is a derived Hox class 3 gene". Proceedings of the National Academy of Sciences. 96 (7): 3786–3789. Bibcode:1999PNAS...96.3786S. doi: 10.1073/pnas.96.7.3786 . PMC   22372 . PMID   10097115.
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  13. ↑ Hoy, Marjorie A. (2019-01-01), Hoy, Marjorie A. (ed.), "Chapter 4 - Genetic Systems, Genome Evolution, and Genetic Control of Embryonic Development in Insects", Insect Molecular Genetics (Fourth Edition), Academic Press, pp. 103–175, doi:10.1016/b978-0-12-815230-0.00004-2, ISBN   978-0-12-815230-0 , retrieved 2024-12-05
  14. ↑ Treisman, Jessica; Desplan, Claude (September 1989). "The products of the Drosophila gap genes hunchback and Krüppel bind to the hunchback promoters". Nature. 341 (6240): 335–337. doi:10.1038/341335a0. ISSN   1476-4687. PMID   2797150.
  15. 1 2 Jaeger, Johannes (2011-01-01). "The gap gene network". Cellular and Molecular Life Sciences. 68 (2): 243–274. doi:10.1007/s00018-010-0536-y. ISSN   1420-9071. PMC   3016493 . PMID   20927566.
  16. ↑ Schroeder, Mark D.; Pearce, Michael; Fak, John; Fan, HongQing; Unnerstall, Ulrich; Emberly, Eldon; Rajewsky, Nikolaus; Siggia, Eric D.; Gaul, Ulrike (2004-08-31). "Transcriptional Control in the Segmentation Gene Network of Drosophila". PLOS Biology. 2 (9): e271. doi: 10.1371/journal.pbio.0020271 . ISSN   1545-7885. PMC   514885 . PMID   15340490.
  17. ↑ Hiromi, Yasushi; Gehring, Walter J. (1987-09-11). "Regulation and function of the Drosophila segmentation gene fushi tarazu". Cell. 50 (6): 963–974. doi:10.1016/0092-8674(87)90523-X. ISSN   0092-8674. PMID   2887293.
  18. ↑ Larsen, Camilla; Bardet, Pierre-Luc; Vincent, Jean-Paul; Alexandre, Cyrille (2008-09-15). "Specification and positioning of parasegment grooves in Drosophila". Developmental Biology. 321 (2): 310–318. doi:10.1016/j.ydbio.2008.04.026. ISSN   0012-1606. PMID   18692780.
  19. ↑ Williams, Terri A.; Nagy, Lisa M. (2017-05-01). "Linking gene regulation to cell behaviors in the posterior growth zone of sequentially segmenting arthropods". Arthropod Structure & Development. Evolution of Segmentation. 46 (3): 380–394. Bibcode:2017ArtSD..46..380W. doi:10.1016/j.asd.2016.10.003. ISSN   1467-8039. PMID   27720841.
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  21. ↑ Frasch, M.; Warrior, R.; Tugwood, J.; Levine, M. (1988-12-01). "Molecular analysis of even-skipped mutants in Drosophila development". Genes & Development. 2 (12b): 1824–1838. doi:10.1101/gad.2.12b.1824. ISSN   0890-9369. PMID   2907321.
  22. ↑ Wilson, Megan J.; Dearden, Peter K. (2012-09-28). "Pair-Rule Gene Orthologues Have Unexpected Maternal Roles in the Honeybee (Apis mellifera)". PLOS ONE. 7 (9): e46490. Bibcode:2012PLoSO...746490W. doi: 10.1371/journal.pone.0046490 . ISSN   1932-6203. PMC   3460886 . PMID   23029534.
  23. ↑ Mohler, Jym (1995-04-01). "Spatial regulation of segment polarity gene expression in the anterior terminal region of the Drosophila blastoderm embryo". Mechanisms of Development. 50 (2): 151–161. doi: 10.1016/0925-4773(94)00332-H . ISSN   0925-4773. PMID   7619727.
  24. ↑ Lim, Jinsung; Choe, Chong Pyo (2020-03-01). "Functional analysis of engrailed in Tribolium segmentation". Mechanisms of Development. 161: 103594. doi:10.1016/j.mod.2019.103594. ISSN   0925-4773. PMID   31778794.
  25. ↑ Swarup, Sharan; Verheyen, Esther M. (2012-06-01). "Wnt/Wingless Signaling in Drosophila". Cold Spring Harbor Perspectives in Biology. 4 (6): a007930. doi:10.1101/cshperspect.a007930. ISSN   1943-0264. PMC   3367557 . PMID   22535229.
  26. ↑ Bejsovec, Amy; Wieschaus, Eric (1993-10-01). "Segment polarity gene interactions modulate epidermal patterning in Drosophila embryos". Development. 119 (2): 501–517. doi:10.1242/dev.119.2.501. ISSN   0950-1991. PMID   8287799.
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